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[netbsd-mini2440.git] / dist / ntp / ntpd / ntp_proto.c

/*      $NetBSD: ntp_proto.c,v 1.6 2006/06/11 19:34:11 kardel Exp $     */

/*
 * ntp_proto.c - NTP version 4 protocol machinery
 *
 * ATTENTION: Get approval from Dave Mills on all changes to this file!
 *
 */
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include "ntpd.h"
#include "ntp_stdlib.h"
#include "ntp_unixtime.h"
#include "ntp_control.h"
#include "ntp_string.h"

#include <stdio.h>

#if defined(VMS) && defined(VMS_LOCALUNIT)      /*wjm*/
#include "ntp_refclock.h"
#endif

#if defined(__FreeBSD__) && __FreeBSD__ >= 3
#include <sys/sysctl.h>
#endif

/*
 * This macro defines the authentication state. If x is 1 authentication
 * is required; othewise it is optional.
 */
#define AUTH(x, y)      ((x) ? (y) == AUTH_OK : (y) == AUTH_OK || \
                            (y) == AUTH_NONE)

/*
 * System variables are declared here. See Section 3.2 of the
 * specification.
 */
u_char  sys_leap;               /* system leap indicator */
u_char  sys_stratum;            /* stratum of system */
s_char  sys_precision;          /* local clock precision (log2 s) */
double  sys_rootdelay;          /* roundtrip delay to primary source */
double  sys_rootdispersion;     /* dispersion to primary source */
u_int32 sys_refid;              /* source/loop in network byte order */
static  double sys_offset;      /* current local clock offset */
l_fp    sys_reftime;            /* time we were last updated */
struct  peer *sys_peer;         /* our current peer */
struct  peer *sys_pps;          /* our PPS peer */
struct  peer *sys_prefer;       /* our cherished peer */
int     sys_kod;                /* kod credit */
int     sys_kod_rate = 2;       /* max kod packets per second */
#ifdef OPENSSL
u_long  sys_automax;            /* maximum session key lifetime */
#endif /* OPENSSL */

/*
 * Nonspecified system state variables.
 */
int     sys_bclient;            /* broadcast client enable */
double  sys_bdelay;             /* broadcast client default delay */
int     sys_calldelay;          /* modem callup delay (s) */
int     sys_authenticate;       /* requre authentication for config */
l_fp    sys_authdelay;          /* authentication delay */
static  u_long sys_authdly[2];  /* authentication delay shift reg */
static  double sys_mindisp = MINDISPERSE; /* min disp increment (s) */
static  double sys_maxdist = MAXDISTANCE; /* selection threshold (s) */
double  sys_jitter;             /* system jitter (s) */
static  int sys_hopper;         /* anticlockhop counter */
static  int sys_maxhop = MAXHOP; /* anticlockhop counter threshold */
int     leap_next;              /* leap consensus */
keyid_t sys_private;            /* private value for session seed */
int     sys_manycastserver;     /* respond to manycast client pkts */
int     peer_ntpdate;           /* active peers in ntpdate mode */
int     sys_survivors;          /* truest of the truechimers */
#ifdef OPENSSL
char    *sys_hostname;          /* gethostname() name */
#endif /* OPENSSL */

/*
 * TOS and multicast mapping stuff
 */
int     sys_floor = 0;          /* cluster stratum floor */
int     sys_ceiling = STRATUM_UNSPEC; /* cluster stratum ceiling */
int     sys_minsane = 1;        /* minimum candidates */
int     sys_minclock = NTP_MINCLOCK; /* minimum survivors */
int     sys_maxclock = NTP_MAXCLOCK; /* maximum candidates */
int     sys_cohort = 0;         /* cohort switch */
int     sys_orphan = STRATUM_UNSPEC + 1; /* orphan stratum */
double  sys_orphandelay = 0;    /* orphan root delay */
int     sys_beacon = BEACON;    /* manycast beacon interval */
int     sys_ttlmax;             /* max ttl mapping vector index */
u_char  sys_ttl[MAX_TTL];       /* ttl mapping vector */

/*
 * Statistics counters
 */
u_long  sys_stattime;           /* time since reset */
u_long  sys_received;           /* packets received */
u_long  sys_processed;          /* packets processed */
u_long  sys_newversionpkt;      /* current version */
u_long  sys_oldversionpkt;      /* recent version */
u_long  sys_unknownversion;     /* invalid version */
u_long  sys_restricted;         /* access denied */
u_long  sys_badlength;          /* bad length or format */
u_long  sys_badauth;            /* bad authentication */
u_long  sys_limitrejected;      /* rate exceeded */

static  double  root_distance   P((struct peer *));
static  void    clock_combine   P((struct peer **, int));
static  void    peer_xmit       P((struct peer *));
static  void    fast_xmit       P((struct recvbuf *, int, keyid_t,
                                    int));
static  void    clock_update    P((void));
static  int     default_get_precision   P((void));
static  int     peer_unfit      P((struct peer *));


/*
 * transmit - Transmit Procedure. See Section 3.4.2 of the
 *      specification.
 */
void
transmit(
        struct peer *peer       /* peer structure pointer */
        )
{
        int     hpoll;

        /*
         * The polling state machine. There are two kinds of machines,
         * those that never expect a reply (broadcast and manycast
         * server modes) and those that do (all other modes). The dance
         * is intricate...
         */
        /*
         * Orphan mode is active when enabled and when no servers less
         * than the orphan statum are available. In this mode packets
         * are sent at the orphan stratum. An orphan with no other
         * synchronization source is an orphan parent. It assumes root
         * delay zero and reference ID the loopback address. All others
         * are orphan children with root delay randomized over a 1-s
         * range. The root delay is used by the election algorithm to
         * select the order of synchronization.
         */
        hpoll = peer->hpoll;
        if (sys_orphan < STRATUM_UNSPEC && sys_peer == NULL) {
                sys_leap = LEAP_NOWARNING;
                sys_stratum = sys_orphan;
                sys_refid = htonl(LOOPBACKADR);
                sys_rootdelay = 0;
                sys_rootdispersion = 0;
        }

        /*
         * In broadcast mode the poll interval is never changed from
         * minpoll.
         */
        if (peer->cast_flags & (MDF_BCAST | MDF_MCAST)) {
                peer->outdate = current_time;
                peer_xmit(peer);
                poll_update(peer, hpoll);
                return;
        }

        /*
         * In manycast mode we start with unity ttl. The ttl is
         * increased by one for each poll until either sys_maxclock
         * servers have been found or the maximum ttl is reached. When
         * sys_maxclock servers are found we stop polling until one or
         * more servers have timed out or until less than minpoll
         * associations turn up. In this case additional better servers
         * are dragged in and preempt the existing ones.
         */
        if (peer->cast_flags & MDF_ACAST) {
                peer->outdate = current_time;
                if (peer->unreach > sys_beacon) {
                        peer->unreach = 0;
                        peer->ttl = 0;
                        peer_xmit(peer);
                } else if (sys_survivors < sys_minclock ||
                    peer_preempt < sys_maxclock) {
                        if (peer->ttl < sys_ttlmax)
                                peer->ttl++;
                        peer_xmit(peer);
                }
                peer->unreach++;
                poll_update(peer, hpoll);
                return;
        }

        /*
         * In unicast modes the dance is much more intricate. It is
         * desigmed to back off whenever possible to minimize network
         * traffic.
         */
        if (peer->burst == 0) {
                u_char oreach;

                /*
                 * Update the reachability status. If not heard for
                 * three consecutive polls, stuff infinity in the clock
                 * filter. 
                 */
                oreach = peer->reach;
                peer->outdate = current_time;
                if (peer == sys_peer)
                        sys_hopper++;
                peer->reach <<= 1;
                if (!(peer->reach & 0x07))
                        clock_filter(peer, 0., 0., MAXDISPERSE);
                if (!peer->reach) {

                        /*
                         * Here the peer is unreachable. If it was
                         * previously reachable, raise a trap.
                         */
                        if (oreach) {
                                report_event(EVNT_UNREACH, peer);
                                peer->timereachable = current_time;
                        }

                        /*
                         * Send a burst if enabled, but only once after
                         * a peer becomes unreachable. If the prempt
                         * flag is dim, bump the unreach counter by one;
                         * otherwise, bump it by three.
                         */
                        if (peer->flags & FLAG_IBURST &&
                            peer->unreach == 0) {
                                peer->burst = NTP_BURST;
                        }
                        if (!(peer->flags & FLAG_PREEMPT))      
                                peer->unreach++;
                        else
                                peer->unreach += 3;
                } else {

                        /*
                         * Here the peer is reachable. Set the poll
                         * interval to the system poll interval. Send a
                         * burst only if enabled and the peer is fit.
                         *
                         * Respond to the peer evaluation produced by
                         * the selection algorithm. If less than the
                         * outlyer level, up the unreach by three. If
                         * there are excess associations, up the unreach
                         * by two if not a candidate and by one if so.
                         */
                        if (!(peer->flags & FLAG_PREEMPT)) {
                                peer->unreach = 0;
                        } else if (peer->status < CTL_PST_SEL_SELCAND) {
                                peer->unreach += 3;
                        } else if (peer_preempt > sys_maxclock) {
                                if (peer->status < CTL_PST_SEL_SYNCCAND)
                                        peer->unreach += 2;
                                else
                                        peer->unreach++;
                        } else {
                                peer->unreach = 0;
                        }
                        hpoll = sys_poll;
                        if (peer->flags & FLAG_BURST &&
                            !peer_unfit(peer))
                                peer->burst = NTP_BURST;
                }

                /*
                 * Watch for timeout. If ephemeral or preemptable, toss
                 * the rascal; otherwise, bump the poll interval.
                 */ 
                if (peer->unreach >= NTP_UNREACH) {
                        if (peer->flags & FLAG_PREEMPT ||
                            !(peer->flags & FLAG_CONFIG)) {
                                peer_clear(peer, "TIME");
                                unpeer(peer);
                                return;
                        } else {
                                hpoll++;
                        }
                }
        } else {
                peer->burst--;

                /*
                 * If a broadcast client at this point, the burst has
                 * concluded, so we switch to client mode and purge the
                 * keylist, since no further transmissions will be made.
                 */
                if (peer->burst == 0) {
                        if (peer->cast_flags & MDF_BCLNT) {
                                peer->hmode = MODE_BCLIENT;
#ifdef OPENSSL
                                key_expire(peer);
#endif /* OPENSSL */
                        }

                        /*
                         * If ntpdate mode and the clock has not been
                         * set and all peers have completed the burst,
                         * we declare a successful failure.
                         */
                        if (mode_ntpdate) {
                                peer_ntpdate--;
                                if (peer_ntpdate == 0) {
                                        msyslog(LOG_NOTICE,
                                            "no reply; clock not set");
                                        exit (0);
                                }
                        }
                }
        }

        /*
         * Do not transmit if in broadcast client mode. 
         */
        if (peer->hmode != MODE_BCLIENT)
                peer_xmit(peer);
        poll_update(peer, hpoll);
}


/*
 * receive - Receive Procedure.  See section 3.4.3 in the specification.
 */
void
receive(
        struct recvbuf *rbufp
        )
{
        register struct peer *peer;     /* peer structure pointer */
        register struct pkt *pkt;       /* receive packet pointer */
        int     hisversion;             /* packet version */
        int     hisleap;                /* packet leap indicator */
        int     hismode;                /* packet mode */
        int     hisstratum;             /* packet stratum */
        int     restrict_mask;          /* restrict bits */
        int     has_mac;                /* length of MAC field */
        int     authlen;                /* offset of MAC field */
        int     is_authentic = 0;       /* cryptosum ok */
        keyid_t skeyid = 0;             /* key ID */
        struct sockaddr_storage *dstadr_sin; /* active runway */
        struct peer *peer2;             /* aux peer structure pointer */
        l_fp    p_org;                  /* origin timestamp */
        l_fp    p_rec;                  /* receive timestamp */
        l_fp    p_xmt;                  /* transmit timestamp */
#ifdef OPENSSL
        keyid_t tkeyid = 0;             /* temporary key ID */
        keyid_t pkeyid = 0;             /* previous key ID */
        struct autokey *ap;             /* autokey structure pointer */
        int     rval;                   /* cookie snatcher */
#endif /* OPENSSL */
        int retcode = AM_NOMATCH;
        int     at_listhead;

        /*
         * Monitor the packet and get restrictions. Note that the packet
         * length for control and private mode packets must be checked
         * by the service routines. Note that no statistics counters are
         * recorded for restrict violations, since these counters are in
         * the restriction routine. Note the careful distinctions here
         * between a packet with a format error and a packet that is
         * simply discarded without prejudice. Some restrictions have to
         * be handled later in order to generate a kiss-of-death packet.
         */
        /*
         * Bogus port check is before anything, since it probably
         * reveals a clogging attack.
         */
        sys_received++;
        if (SRCPORT(&rbufp->recv_srcadr) == 0) {
                sys_badlength++;
                return;                         /* bogus port */
        }
        at_listhead = ntp_monitor(rbufp);
        restrict_mask = restrictions(&rbufp->recv_srcadr, at_listhead);
#ifdef DEBUG
        if (debug > 1)
                printf("receive: at %ld %s<-%s flags %x restrict %03x\n",
                    current_time, stoa(&rbufp->dstadr->sin),
                    stoa(&rbufp->recv_srcadr),
                    rbufp->dstadr->flags, restrict_mask);
#endif
        if (restrict_mask & RES_IGNORE) {
                sys_restricted++;
                return;                         /* ignore everything */
        }
        pkt = &rbufp->recv_pkt;
        hisversion = PKT_VERSION(pkt->li_vn_mode);
        hisleap = PKT_LEAP(pkt->li_vn_mode);
        hismode = (int)PKT_MODE(pkt->li_vn_mode);
        hisstratum = PKT_TO_STRATUM(pkt->stratum);
        if (hismode == MODE_PRIVATE) {
                if (restrict_mask & RES_NOQUERY) {
                        sys_restricted++;
                        return;                 /* no query private */
                }
                process_private(rbufp, ((restrict_mask &
                    RES_NOMODIFY) == 0));
                return;
        }
        if (hismode == MODE_CONTROL) {
                if (restrict_mask & RES_NOQUERY) {
                        sys_restricted++;
                        return;                 /* no query control */
                }
                process_control(rbufp, restrict_mask);
                return;
        }
        if (restrict_mask & RES_DONTSERVE) {
                sys_restricted++;
                return;                         /* no time */
        }
        if (rbufp->recv_length < LEN_PKT_NOMAC) {
                sys_badlength++;
                return;                         /* runt packet */
        }
        
        /*
         * Version check must be after the query packets, since they
         * intentionally use early version.
         */
        if (hisversion == NTP_VERSION) {
                sys_newversionpkt++;            /* new version */
        } else if (!(restrict_mask & RES_VERSION) && hisversion >=
            NTP_OLDVERSION) {
                sys_oldversionpkt++;            /* previous version */
        } else {
                sys_unknownversion++;
                return;                         /* old version */
        }

        /*
         * Figure out his mode and validate the packet. This has some
         * legacy raunch that probably should be removed. In very early
         * NTP versions mode 0 was equivalent to what later versions
         * would interpret as client mode.
         */
        if (hismode == MODE_UNSPEC) {
                if (hisversion == NTP_OLDVERSION) {
                        hismode = MODE_CLIENT;
                } else {
                        sys_badlength++;
                        return;                 /* invalid mode */
                }
        }

        /*
         * Parse the extension field if present. We figure out whether
         * an extension field is present by measuring the MAC size. If
         * the number of words following the packet header is 0, no MAC
         * is present and the packet is not authenticated. If 1, the
         * packet is a crypto-NAK; if 3, the packet is authenticated
         * with DES; if 5, the packet is authenticated with MD5. If 2 or
         * 4, the packet is a runt and discarded forthwith. If greater
         * than 5, an extension field is present, so we subtract the
         * length of the field and go around again.
         */
        authlen = LEN_PKT_NOMAC;
        has_mac = rbufp->recv_length - authlen;
        while (has_mac > 0) {
                int temp;

                if (has_mac % 4 != 0 || has_mac < 0) {
                        sys_badlength++;
                        return;                 /* bad MAC length */
                }
                if (has_mac == 1 * 4 || has_mac == 3 * 4 || has_mac ==
                    MAX_MAC_LEN) {
                        skeyid = ntohl(((u_int32 *)pkt)[authlen / 4]);
                        break;

                } else if (has_mac > MAX_MAC_LEN) {
                        temp = ntohl(((u_int32 *)pkt)[authlen / 4]) &
                            0xffff;
                        if (temp < 4 || temp > NTP_MAXEXTEN || temp % 4
                            != 0) {
                                sys_badlength++;
                                return;         /* bad MAC length */
                        }
                        authlen += temp;
                        has_mac -= temp;
                } else {
                        sys_badlength++;
                        return;                 /* bad MAC length */
                }
        }
#ifdef OPENSSL
        pkeyid = tkeyid = 0;
#endif /* OPENSSL */

        /*
         * We have tossed out as many buggy packets as possible early in
         * the game to reduce the exposure to a clogging attack. Now we
         * have to burn some cycles to find the association and
         * authenticate the packet if required. Note that we burn only
         * MD5 cycles, again to reduce exposure. There may be no
         * matching association and that's okay.
         *
         * More on the autokey mambo. Normally the local interface is
         * found when the association was mobilized with respect to a
         * designated remote address. We assume packets arriving from
         * the remote address arrive via this interface and the local
         * address used to construct the autokey is the unicast address
         * of the interface. However, if the sender is a broadcaster,
         * the interface broadcast address is used instead.
         & Notwithstanding this technobabble, if the sender is a
         * multicaster, the broadcast address is null, so we use the
         * unicast address anyway. Don't ask.
         */
        peer = findpeer(&rbufp->recv_srcadr, rbufp->dstadr,  hismode,
            &retcode);
        dstadr_sin = &rbufp->dstadr->sin;
        NTOHL_FP(&pkt->org, &p_org);
        NTOHL_FP(&pkt->rec, &p_rec);
        NTOHL_FP(&pkt->xmt, &p_xmt);

        /*
         * Authentication is conditioned by three switches:
         *
         * NOPEER  (RES_NOPEER) do not mobilize an association unless
         *         authenticated
         * NOTRUST (RES_DONTTRUST) do not allow access unless
         *         authenticated (implies NOPEER)
         * enable  (sys_authenticate) master NOPEER switch, by default
         *         on
         *
         * The NOPEER and NOTRUST can be specified on a per-client basis
         * using the restrict command. The enable switch if on implies
         * NOPEER for all clients. There are four outcomes:
         *
         * NONE    The packet has no MAC.
         * OK      the packet has a MAC and authentication succeeds
         * ERROR   the packet has a MAC and authentication fails
         * CRYPTO  crypto-NAK. The MAC has four octets only.
         *
         * Note: The AUTH(x, y) macro is used to filter outcomes. If x
         * is zero, acceptable outcomes of y are NONE and OK. If x is
         * one, the only acceptable outcome of y is OK.
         */
        if (has_mac == 0) {
                is_authentic = AUTH_NONE; /* not required */
#ifdef DEBUG
                if (debug)
                        printf("receive: at %ld %s<-%s mode %d code %d auth %d\n",
                            current_time, stoa(dstadr_sin),
                            stoa(&rbufp->recv_srcadr), hismode, retcode,
                            is_authentic);
#endif
        } else if (has_mac == 4) {
                        is_authentic = AUTH_CRYPTO; /* crypto-NAK */
#ifdef DEBUG
                if (debug)
                        printf(
                            "receive: at %ld %s<-%s mode %d code %d keyid %08x len %d mac %d auth %d\n",
                            current_time, stoa(dstadr_sin),
                            stoa(&rbufp->recv_srcadr), hismode, retcode,
                            skeyid, authlen, has_mac, is_authentic);
#endif
        } else {
#ifdef OPENSSL
                /*
                 * For autokey modes, generate the session key
                 * and install in the key cache. Use the socket
                 * broadcast or unicast address as appropriate.
                 */
                if (skeyid > NTP_MAXKEY) {
                
                        /*
                         * More on the autokey dance (AKD). A cookie is
                         * constructed from public and private values.
                         * For broadcast packets, the cookie is public
                         * (zero). For packets that match no
                         * association, the cookie is hashed from the
                         * addresses and private value. For server
                         * packets, the cookie was previously obtained
                         * from the server. For symmetric modes, the
                         * cookie was previously constructed using an
                         * agreement protocol; however, should PKI be
                         * unavailable, we construct a fake agreement as
                         * the EXOR of the peer and host cookies.
                         *
                         * hismode      ephemeral       persistent
                         * =======================================
                         * active       0               cookie#
                         * passive      0%              cookie#
                         * client       sys cookie      0%
                         * server       0%              sys cookie
                         * broadcast    0               0
                         *
                         * # if unsync, 0
                         * % can't happen
                         */
                        if (hismode == MODE_BROADCAST) {

                                /*
                                 * For broadcaster, use the interface
                                 * broadcast address when available;
                                 * otherwise, use the unicast address
                                 * found when the association was
                                 * mobilized. However, if this is from
                                 * the wildcard interface, game over.
                                 */
                                if (crypto_flags && rbufp->dstadr ==
                                    any_interface) {
                                        sys_restricted++;
                                        return;      /* no wildcard */
                                }
                                pkeyid = 0;
                                if (!SOCKNUL(&rbufp->dstadr->bcast))
                                        dstadr_sin =
                                            &rbufp->dstadr->bcast;
                        } else if (peer == NULL) {
                                pkeyid = session_key(
                                    &rbufp->recv_srcadr, dstadr_sin, 0,
                                    sys_private, 0);
                        } else {
                                pkeyid = peer->pcookie;
                        }

                        /*
                         * The session key includes both the public
                         * values and cookie. In case of an extension
                         * field, the cookie used for authentication
                         * purposes is zero. Note the hash is saved for
                         * use later in the autokey mambo.
                         */
                        if (authlen > LEN_PKT_NOMAC && pkeyid != 0) {
                                session_key(&rbufp->recv_srcadr,
                                    dstadr_sin, skeyid, 0, 2);
                                tkeyid = session_key(
                                    &rbufp->recv_srcadr, dstadr_sin,
                                    skeyid, pkeyid, 0);
                        } else {
                                tkeyid = session_key(
                                    &rbufp->recv_srcadr, dstadr_sin,
                                    skeyid, pkeyid, 2);
                        }

                }
#endif /* OPENSSL */

                /*
                 * Compute the cryptosum. Note a clogging attack may
                 * succeed in bloating the key cache. If an autokey,
                 * purge it immediately, since we won't be needing it
                 * again. If the packet is authentic, it can mobilize an
                 * association. Note that there is no key zero.
                 */
                if (!authdecrypt(skeyid, (u_int32 *)pkt, authlen,
                    has_mac)) {
                        is_authentic = AUTH_ERROR;
                        sys_badauth++;
                } else {
                        is_authentic = AUTH_OK;
                }
#ifdef OPENSSL
                if (skeyid > NTP_MAXKEY)
                        authtrust(skeyid, 0);
#endif /* OPENSSL */
#ifdef DEBUG
                if (debug)
                        printf(
                            "receive: at %ld %s<-%s mode %d code %d keyid %08x len %d mac %d auth %d\n",
                            current_time, stoa(dstadr_sin),
                            stoa(&rbufp->recv_srcadr), hismode, retcode,
                            skeyid, authlen, has_mac, is_authentic);
#endif
        }

        /*
         * The association matching rules are implemented by a set of
         * routines and an association table. A packet matching an
         * association is processed by the peer process for that
         * association. If there are no errors, an ephemeral association
         * is mobilized: a broadcast packet mobilizes a broadcast client
         * aassociation; a manycast server packet mobilizes a manycast
         * client association; a symmetric active packet mobilizes a
         * symmetric passive association.
         */
        switch (retcode) {

        /*
         * This is a client mode packet not matching any association. If
         * an ordinary client, simply toss a server mode packet back
         * over the fence. If a manycast client, we have to work a
         * little harder.
         */
        case AM_FXMIT:

                /*
                 * The vanilla case is when this is not a multicast
                 * interface. If authentication succeeds, return a
                 * server mode packet; if not and the key ID is nonzero,
                 * return a crypto-NAK.
                 */
                if (!(rbufp->dstadr->flags & INT_MCASTOPEN)) {
                        if (AUTH(restrict_mask & RES_DONTTRUST,
                           is_authentic))
                                fast_xmit(rbufp, MODE_SERVER, skeyid,
                                    restrict_mask);
                        else if (is_authentic == AUTH_ERROR)
                                fast_xmit(rbufp, MODE_SERVER, 0,
                                    restrict_mask);
                        return;                 /* hooray */
                }

                /*
                 * This must be manycast. Do not respond if not
                 * configured as a manycast server.
                 */
                if (!sys_manycastserver) {
                        sys_restricted++;
                        return;                 /* not enabled */
                }

                /*
                 * Do not respond if unsynchronized or stratum is below
                 * the floor or at or above the ceiling.
                 */
                if (sys_leap == LEAP_NOTINSYNC || sys_stratum <
                    sys_floor || sys_stratum >= sys_ceiling)
                        return;                 /* bad stratum */

                /*
                 * Do not respond if our stratum is greater than the
                 * manycaster or it has already synchronized to us.
                 */
                if (sys_peer == NULL || hisstratum < sys_stratum ||
                    (sys_cohort && hisstratum == sys_stratum) ||
                    rbufp->dstadr->addr_refid == pkt->refid)
                        return;                 /* no help */

                /*
                 * Respond only if authentication succeeds. Don't do a
                 * crypto-NAK, as that would not be useful.
                 */
                if (AUTH(restrict_mask & RES_DONTTRUST, is_authentic))
                        fast_xmit(rbufp, MODE_SERVER, skeyid,
                            restrict_mask);

                return;                         /* hooray */

        /*
         * This is a server mode packet returned in response to a client
         * mode packet sent to a multicast group address. The origin
         * timestamp is a good nonce to reliably associate the reply
         * with what was sent. If there is no match, that's curious and
         * could be an intruder attempting to clog, so we just ignore
         * it.
         *
         * If the packet is authentic and the manycast association is
         * found, we mobilize a client association and copy pertinent
         * variables from the manycast association to the new client
         * association. If not, just ignore the packet.
         *
         * There is an implosion hazard at the manycast client, since
         * the manycast servers send the server packet immediately. If
         * the guy is already here, don't fire up a duplicate.
         */
        case AM_MANYCAST:
                if (!AUTH(sys_authenticate | (restrict_mask &
                    (RES_NOPEER | RES_DONTTRUST)), is_authentic))
                        return;                 /* bad auth */

                if ((peer2 = findmanycastpeer(rbufp)) == NULL) {
                        sys_restricted++;
                        return;                 /* not enabled */
                }
                if ((peer = newpeer(&rbufp->recv_srcadr,
                    rbufp->dstadr, MODE_CLIENT,
                    hisversion, NTP_MINDPOLL, NTP_MAXDPOLL,
                    FLAG_IBURST | FLAG_PREEMPT, MDF_UCAST | MDF_ACLNT,
                    0, skeyid)) == NULL)
                        return;                 /* system error */

                /*
                 * We don't need these, but it warms the billboards.
                 */
                peer->ttl = peer2->ttl;
                break;

        /*
         * This is the first packet received from a broadcast server. If
         * the packet is authentic and we are enabled as broadcast
         * client, mobilize a broadcast client association. We don't
         * kiss any frogs here.
         */
        case AM_NEWBCL:
                if (!AUTH(sys_authenticate | (restrict_mask &
                    (RES_NOPEER | RES_DONTTRUST)), is_authentic))
                        return;                 /* bad auth */

                /*
                 * Do not respond if unsynchronized or stratum is below
                 * the floor or at or above the ceiling.
                 */
                if (hisleap == LEAP_NOTINSYNC || hisstratum <
                    sys_floor || hisstratum >= sys_ceiling)
                        return;                 /* bad stratum */

                switch (sys_bclient) {

                /*
                 * If not enabled, just skedaddle.
                 */
                case 0:
                        sys_restricted++;
                        return;                 /* not enabled */

                /*
                 * Execute the initial volley in order to calibrate the
                 * propagation delay and run the Autokey protocol, if
                 * enabled.
                 */
                case 1:
                        if ((peer = newpeer(&rbufp->recv_srcadr,
                            rbufp->dstadr, MODE_CLIENT, hisversion,
                            NTP_MINDPOLL, NTP_MAXDPOLL, FLAG_MCAST |
                            FLAG_IBURST, MDF_BCLNT, 0, skeyid)) ==
                            NULL)
                                return;         /* system error */
#ifdef OPENSSL
                        if (skeyid > NTP_MAXKEY)
                                crypto_recv(peer, rbufp);
#endif /* OPENSSL */
                        return;                 /* hooray */


                /*
                 * Do not execute the initial volley.
                 */
                case 2:
#ifdef OPENSSL
                        /*
                         * If a two-way exchange is not possible,
                         * neither is Autokey.
                         */
                        if (skeyid > NTP_MAXKEY) {
                                msyslog(LOG_INFO,
                                    "receive: autokey requires two-way communication");
                                return;         /* no autokey */
                        }
#endif /* OPENSSL */
                        if ((peer = newpeer(&rbufp->recv_srcadr,
                            rbufp->dstadr, MODE_BCLIENT, hisversion,
                            NTP_MINDPOLL, NTP_MAXDPOLL, 0, MDF_BCLNT, 0,
                            skeyid)) == NULL)
                                return;         /* system error */
                }
                break;

        /*
         * This is the first packet received from a symmetric active
         * peer. If the packet is authentic and the first he sent,
         * mobilize a passive association. If not, kiss the frog.
         */
        case AM_NEWPASS:

                /*
                 * If the inbound packet is correctly authenticated and
                 * enabled, a symmetric passive association is
                 * mobilized. If not but correctly authenticated, a
                 * symmetric active response is sent. If authentication
                 * fails, send a crypto-NAK packet. 
                 */
                if (!AUTH(restrict_mask & RES_DONTTRUST, is_authentic))
                    {
                        if (is_authentic == AUTH_ERROR)
                                fast_xmit(rbufp, MODE_ACTIVE, 0,
                                    restrict_mask);
                        return;                 /* bad auth */
                }
                if (!AUTH(sys_authenticate | (restrict_mask &
                    RES_NOPEER), is_authentic)) {
                        fast_xmit(rbufp, MODE_ACTIVE, skeyid,
                            restrict_mask);
                        return;                 /* hooray */
                }

                /*
                 * Do not respond if stratum is below the floor.
                 */
                if (hisstratum < sys_floor)
                        return;                 /* bad stratum */

                if ((peer = newpeer(&rbufp->recv_srcadr,
                    rbufp->dstadr, MODE_PASSIVE, hisversion,
                    NTP_MINDPOLL, NTP_MAXDPOLL, 0, MDF_UCAST, 0,
                    skeyid)) == NULL)
                        return;                 /* system error */
                break;

        /*
         * Process regular packet. Nothing special.
         */
        case AM_PROCPKT:
                break;

        /*
         * A passive packet matches a passive association. This is
         * usually the result of reconfiguring a client on the fly. As
         * this association might be legitamate and this packet an
         * attempt to deny service, just ignore it.
         */
        case AM_ERR:
                return;

        /*
         * For everything else there is the bit bucket.
         */
        default:
                return;
        }
        peer->flash &= ~PKT_TEST_MASK;

        /*
         * Next comes a rigorous schedule of timestamp checking. If the
         * transmit timestamp is zero, the server is horribly broken.
         */
        if (L_ISZERO(&p_xmt)) {
                return;                         /* read rfc1305 */

        /*
         * If the transmit timestamp duplicates a previous one, the
         * packet is a replay. This prevents the bad guys from replaying
         * the most recent packet, authenticated or not.
         */
        } else if (L_ISEQU(&peer->org, &p_xmt)) {
                peer->flash |= TEST1;
                peer->oldpkt++;
                return;                         /* duplicate packet */
        

        /*
         * If this is a broadcast mode packet, skip further checking.
         */
        } else if (hismode != MODE_BROADCAST) {
                if (L_ISZERO(&p_org))
                        peer->flash |= TEST3;   /* protocol unsynch */
                else if (!L_ISEQU(&p_org, &peer->xmt))
                        peer->flash |= TEST2;   /* bogus packet */
        }

        /*
         * Update the origin and destination timestamps. If
         * unsynchronized or bogus abandon ship. If the crypto machine
         * breaks, light the crypto bit and plaint the log.
         */
        peer->org = p_xmt;
        peer->rec = rbufp->recv_time;
        if (peer->flash & PKT_TEST_MASK) {
#ifdef OPENSSL
                if (crypto_flags && (peer->flags & FLAG_SKEY)) {
                        rval = crypto_recv(peer, rbufp);
                        if (rval != XEVNT_OK) {
                                peer_clear(peer, "CRYP");
                                peer->flash |= TEST9; /* crypto error */
                        }
                }
#endif /* OPENSSL */
                return;                         /* unsynch */
        }

        /*
         * The timestamps are valid and the receive packet matches the
         * last one sent. If the packet is a crypto-NAK, the server
         * might have just changed keys. We reset the association
         * and restart the protocol.
         */
        if (is_authentic == AUTH_CRYPTO) {
                peer_clear(peer, "AUTH");
                return;                         /* crypto-NAK */

        /* 
         * If the association is authenticated, the key ID is nonzero
         * and received packets must be authenticated. This is designed
         * to avoid a bait-and-switch attack, which was possible in past
         * versions. If symmetric modes, return a crypto-NAK. The peer
         * should restart the protocol.
         */
        } else if (!AUTH(peer->keyid || (restrict_mask & RES_DONTTRUST),
            is_authentic)) {
                peer->flash |= TEST5;
                if (hismode == MODE_ACTIVE || hismode == MODE_PASSIVE)
                        fast_xmit(rbufp, MODE_ACTIVE, 0, restrict_mask);
                return;                         /* bad auth */
        }

        /*
         * That was hard and I am sweaty, but the packet is squeaky
         * clean. Get on with real work.
         */
        peer->received++;
        peer->timereceived = current_time;
        if (is_authentic == AUTH_OK)
                peer->flags |= FLAG_AUTHENTIC;
        else
                peer->flags &= ~FLAG_AUTHENTIC;
#ifdef OPENSSL
        /*
         * More autokey dance. The rules of the cha-cha are as follows:
         *
         * 1. If there is no key or the key is not auto, do nothing.
         *
         * 2. If this packet is in response to the one just previously
         *    sent or from a broadcast server, do the extension fields.
         *    Otherwise, assume bogosity and bail out.
         *
         * 3. If an extension field contains a verified signature, it is
         *    self-authenticated and we sit the dance.
         *
         * 4. If this is a server reply, check only to see that the
         *    transmitted key ID matches the received key ID.
         *
         * 5. Check to see that one or more hashes of the current key ID
         *    matches the previous key ID or ultimate original key ID
         *    obtained from the broadcaster or symmetric peer. If no
         *    match, sit the dance and wait for timeout.
         *
         * In case of crypto error, fire the orchestra and stop dancing.
         * This is considered a permanant error, so light the crypto bit
         * to suppress further requests. If preemptable or ephemeral,
         * scuttle the ship.
         */
        if (crypto_flags && (peer->flags & FLAG_SKEY)) {
                peer->flash |= TEST8;
                rval = crypto_recv(peer, rbufp);
                if (rval != XEVNT_OK) {
                        peer_clear(peer, "CRYP");
                        peer->flash |= TEST9;   /* crypto error */
                        if (peer->flags & FLAG_PREEMPT ||
                            !(peer->flags & FLAG_CONFIG))
                                unpeer(peer);
                        return;

                } else if (hismode == MODE_SERVER) {
                        if (skeyid == peer->keyid)
                                peer->flash &= ~TEST8;
                } else if (!(peer->flash & TEST8)) {
                        peer->pkeyid = skeyid;
                } else if ((ap = (struct autokey *)peer->recval.ptr) !=
                    NULL) {
                        int i;

                        for (i = 0; ; i++) {
                                if (tkeyid == peer->pkeyid ||
                                    tkeyid == ap->key) {
                                        peer->flash &= ~TEST8;
                                        peer->pkeyid = skeyid;
                                        break;
                                }
                                if (i > ap->seq)
                                        break;
                                tkeyid = session_key(
                                    &rbufp->recv_srcadr, dstadr_sin,
                                    tkeyid, pkeyid, 0);
                        }
                }
                if (!(peer->crypto & CRYPTO_FLAG_PROV)) /* test 9 */
                        peer->flash |= TEST8;   /* not proventic */

                /*
                 * If the transmit queue is nonempty, clamp the host
                 * poll interval to the packet poll interval.
                 */
                if (peer->cmmd != 0) {
                        peer->ppoll = pkt->ppoll;
                        poll_update(peer, peer->hpoll);
                }
        }
#endif /* OPENSSL */

        /*
         * The dance is complete and the flash bits have been lit. Toss
         * the packet over the fence for processing, which may light up
         * more flashers.
         */
        process_packet(peer, pkt);

        /*
         * Well, that was nice. If TEST4 is lit, either the crypto
         * machine jammed or a kiss-o'-death packet flew in, either of
         * which is fatal.
         */
        if (peer->flash & TEST4) {
                msyslog(LOG_INFO, "receive: fatal error %04x for %s",
                    peer->flash, stoa(&peer->srcadr));
                return;
        }
}


/*
 * process_packet - Packet Procedure, a la Section 3.4.4 of the
 *      specification. Or almost, at least. If we're in here we have a
 *      reasonable expectation that we will be having a long term
 *      relationship with this host.
 */
void
process_packet(
        register struct peer *peer,
        register struct pkt *pkt
        )
{
        double  t34, t21;
        double  p_offset, p_del, p_disp;
        l_fp    p_rec, p_xmt, p_org, p_reftime;
        l_fp    ci;
        u_char  pmode, pleap, pstratum;

        sys_processed++;
        peer->processed++;
        p_del = FPTOD(NTOHS_FP(pkt->rootdelay));
        p_disp = FPTOD(NTOHS_FP(pkt->rootdispersion));
        NTOHL_FP(&pkt->reftime, &p_reftime);
        NTOHL_FP(&pkt->rec, &p_rec);
        NTOHL_FP(&pkt->xmt, &p_xmt);
        pmode = PKT_MODE(pkt->li_vn_mode);
        pleap = PKT_LEAP(pkt->li_vn_mode);
        if (pmode != MODE_BROADCAST)
                NTOHL_FP(&pkt->org, &p_org);
        else
                p_org = peer->rec;
        pstratum = PKT_TO_STRATUM(pkt->stratum);

        /*
         * Test for kiss-o'death packet)
         */
        if (pleap == LEAP_NOTINSYNC && pstratum == STRATUM_UNSPEC) {
                if (memcmp(&pkt->refid, "DENY", 4) == 0) {
                        peer_clear(peer, "DENY");
                        peer->flash |= TEST4;   /* access denied */
                }
        }

        /*
         * Capture the header values.
         */
        record_raw_stats(&peer->srcadr, peer->dstadr ? &peer->dstadr->sin : NULL, &p_org,
            &p_rec, &p_xmt, &peer->rec);
        peer->leap = pleap;
        peer->stratum = min(pstratum, STRATUM_UNSPEC);
        peer->pmode = pmode;
        peer->ppoll = pkt->ppoll;
        peer->precision = pkt->precision;
        peer->rootdelay = p_del;
        peer->rootdispersion = p_disp;
        peer->refid = pkt->refid;               /* network byte order */
        peer->reftime = p_reftime;

        /*
         * Verify the server is synchronized; that is, the leap bits and
         * stratum are valid, the root delay and root dispersion are
         * valid and the reference timestamp is not later than the
         * transmit timestamp.
         */
        if (pleap == LEAP_NOTINSYNC ||          /* test 6 */
            pstratum < sys_floor || pstratum >= sys_ceiling)
                peer->flash |= TEST6;           /* peer not synch */
        if (p_del < 0 || p_disp < 0 || p_del /  /* test 7 */
            2 + p_disp >= MAXDISPERSE || !L_ISHIS(&p_xmt, &p_reftime))
                peer->flash |= TEST7;           /* bad header */

        /*
         * If any tests fail at this point, the packet is discarded.
         * Note that some flashers may have already been set in the
         * receive() routine.
         */
        if (peer->flash & PKT_TEST_MASK) {
#ifdef DEBUG
                if (debug)
                        printf("packet: flash header %04x\n",
                            peer->flash);
#endif
                return;
        }
        if (!(peer->reach)) {
                report_event(EVNT_REACH, peer);
                peer->timereachable = current_time;
        }
        poll_update(peer, peer->hpoll);
        peer->reach |= 1;

        /*
         * For a client/server association, calculate the clock offset,
         * roundtrip delay and dispersion. The equations are reordered
         * from the spec for more efficient use of temporaries. For a
         * broadcast association, offset the last measurement by the
         * computed delay during the client/server volley. Note that
         * org has been set to the time of last reception. Note the
         * computation of dispersion includes the system precision plus
         * that due to the frequency error since the origin time.
         *
         * It is very important to respect the hazards of overflow. The
         * only permitted operation on raw timestamps is subtraction,
         * where the result is a signed quantity spanning from 68 years
         * in the past to 68 years in the future. To avoid loss of
         * precision, these calculations are done using 64-bit integer
         * arithmetic. However, the offset and delay calculations are
         * sums and differences of these first-order differences, which
         * if done using 64-bit integer arithmetic, would be valid over
         * only half that span. Since the typical first-order
         * differences are usually very small, they are converted to 64-
         * bit doubles and all remaining calculations done in floating-
         * point arithmetic. This preserves the accuracy while retaining
         * the 68-year span.
         *
         * Let t1 = p_org, t2 = p_rec, t3 = p_xmt, t4 = peer->rec:
         */
        ci = p_xmt;                     /* t3 - t4 */
        L_SUB(&ci, &peer->rec);
        LFPTOD(&ci, t34);
        ci = p_rec;                     /* t2 - t1 */
        L_SUB(&ci, &p_org);
        LFPTOD(&ci, t21);
        ci = peer->rec;                 /* t4 - t1 */
        L_SUB(&ci, &p_org);

        /*
         * If running in a broadcast association, the clock offset is
         * (t1 - t0) corrected by the one-way delay, but we can't
         * measure that directly. Therefore, we start up in MODE_CLIENT
         * mode, set FLAG_MCAST and exchange eight messages to determine
         * the clock offset. When the last message is sent, we switch to
         * MODE_BCLIENT mode. The next broadcast message after that
         * computes the broadcast offset and clears FLAG_MCAST.
         */
        if (pmode == MODE_BROADCAST) {
                p_offset = t34;
                if (peer->flags & FLAG_MCAST) {
                        peer->estbdelay = peer->offset - p_offset;
                        if (peer->hmode == MODE_CLIENT)
                                return;

                        peer->flags &= ~(FLAG_MCAST | FLAG_BURST);
                }
                p_offset += peer->estbdelay;
                p_del = peer->delay;
                p_disp = 0;
        } else {
                p_offset = (t21 + t34) / 2.;
                p_del = t21 - t34;
                LFPTOD(&ci, p_disp);
                p_disp = LOGTOD(sys_precision) +
                    LOGTOD(peer->precision) + clock_phi * p_disp;
        }
        p_del = max(p_del, LOGTOD(sys_precision));
        clock_filter(peer, p_offset, p_del, p_disp);
        record_peer_stats(&peer->srcadr, ctlpeerstatus(peer),
            peer->offset, peer->delay, peer->disp, peer->jitter);
}


/*
 * clock_update - Called at system process update intervals.
 */
static void
clock_update(void)
{
        u_char  oleap;
        u_char  ostratum;
        double  dtemp;

        /*
         * There must be a system peer at this point. If we just changed
         * the system peer, but have a newer sample from the old one,
         * wait until newer data are available.
         */
        if (sys_poll < sys_peer->minpoll)
                sys_poll = sys_peer->minpoll;
        if (sys_poll > sys_peer->maxpoll)
                sys_poll = sys_peer->maxpoll;
        poll_update(sys_peer, sys_poll);
        if (sys_peer->epoch <= sys_clocktime)
                return;

#ifdef DEBUG
        if (debug)
                printf("clock_update: at %ld assoc %d \n", current_time,
                    peer_associations);
#endif
        oleap = sys_leap;
        ostratum = sys_stratum;
        switch (local_clock(sys_peer, sys_offset)) {

        /*
         * Clock exceeds panic threshold. Life as we know it ends.
         */
        case -1:
                report_event(EVNT_SYSFAULT, NULL);
                exit (-1);
                /* not reached */

        /*
         * Clock was stepped. Flush all time values of all peers.
         */
        case 2:
                clear_all();
                sys_leap = LEAP_NOTINSYNC;
                sys_stratum = STRATUM_UNSPEC;
                sys_peer = NULL;
                sys_rootdelay = 0;
                sys_rootdispersion = 0;
                memcpy(&sys_refid, "STEP", 4);
                report_event(EVNT_CLOCKRESET, NULL);
                break;

        /*
         * Clock was slewed. Update the system stratum, leap bits, root
         * delay, root dispersion, reference ID and reference time. If
         * the leap changes, we gotta reroll the keys. Except for
         * reference clocks, the minimum dispersion increment is not
         * less than sys_mindisp.
         */
        case 1:
                sys_leap = leap_next;
                sys_stratum = min(sys_peer->stratum + 1,
                    STRATUM_UNSPEC);
                sys_reftime = sys_peer->rec;

                /*
                 * In orphan mode the stratum defaults to the orphan
                 * stratum. The root delay is set to a random value
                 * generated at startup. The root dispersion is set from
                 * the peer dispersion; the peer root dispersion is
                 * ignored.
                 */
                dtemp = sys_peer->disp + clock_phi * (current_time -
                    sys_peer->update) + sys_jitter +
                    fabs(sys_peer->offset);
#ifdef REFCLOCK
                if (!(sys_peer->flags & FLAG_REFCLOCK) && dtemp <
                    sys_mindisp)
                        dtemp = sys_mindisp;
#else
                if (dtemp < sys_mindisp)
                        dtemp = sys_mindisp;
#endif /* REFCLOCK */
                if (sys_stratum >= sys_orphan) {
                        sys_stratum = sys_orphan;
                        sys_rootdelay = sys_peer->delay;
                        sys_rootdispersion = dtemp;
                } else {
                        sys_rootdelay = sys_peer->delay +
                            sys_peer->rootdelay;
                        sys_rootdispersion = dtemp +
                            sys_peer->rootdispersion;
                }
                if (oleap == LEAP_NOTINSYNC) {
                        report_event(EVNT_SYNCCHG, NULL);
#ifdef OPENSSL
                        expire_all();
                        crypto_update();
#endif /* OPENSSL */
                }
                break;
        /*
         * Popcorn spike or step threshold exceeded. Pretend it never
         * happened.
         */
        default:
                break;
        }
        if (ostratum != sys_stratum)
                report_event(EVNT_PEERSTCHG, NULL);
}


/*
 * poll_update - update peer poll interval
 */
void
poll_update(
        struct peer *peer,
        int     mpoll
        )
{
        int     hpoll;

        /*
         * This routine figures out when the next poll should be sent.
         * That turns out to be wickedly complicated. The big problem is
         * that sometimes the time for the next poll is in the past.
         * Watch out for races here between the receive process and the
         * poll process. The key assertion is that, if nextdate equals
         * current_time, the call is from the poll process; otherwise,
         * it is from the receive process.
         *
         * First, bracket the poll interval according to the type of
         * association and options. If a fixed interval is configured,
         * use minpoll. This primarily is for reference clocks, but
         * works for any association.
         */
        if (peer->flags & FLAG_FIXPOLL) {
                hpoll = peer->minpoll;

        /*
         * The ordinary case; clamp the poll interval between minpoll
         * and maxpoll.
         */
        } else {
                hpoll = max(min(peer->maxpoll, mpoll), peer->minpoll);
        }
#ifdef OPENSSL
        /*
         * Bit of crass arrogance at this point. If the poll interval
         * has changed and we have a keylist, the lifetimes in the
         * keylist are probably bogus. In this case purge the keylist
         * and regenerate it later.
         */
        if (hpoll != peer->hpoll)
                key_expire(peer);
#endif /* OPENSSL */
        peer->hpoll = hpoll;

        /*
         * Now we figure out if there is an override. If during the
         * crypto protocol and a message is pending, make it wait not
         * more than two seconds.
         */
#ifdef OPENSSL
        if (peer->cmmd != NULL && (sys_leap != LEAP_NOTINSYNC ||
            peer->crypto)) {
                peer->nextdate = current_time + RESP_DELAY;

        /*
         * If we get called from the receive routine while a burst is
         * pending, just slink away. If from the poll routine and a
         * reference clock or a pending crypto response, delay for one
         * second. If this is the first sent in a burst, wait for the
         * modem to come up. For others in the burst, delay two seconds.
         */
        } else if (peer->burst > 0) {
#else /* OPENSSL */
        if (peer->burst > 0) {
#endif /* OPENSSL */
                if (peer->nextdate != current_time)
                        return;
#ifdef REFCLOCK
                else if (peer->flags & FLAG_REFCLOCK)
                        peer->nextdate += RESP_DELAY;
#endif /* REFCLOCK */
                else if (peer->flags & (FLAG_IBURST | FLAG_BURST) &&
                    peer->burst == NTP_BURST)
                        peer->nextdate += sys_calldelay;
                else
                        peer->nextdate += BURST_DELAY;
        /*
         * The ordinary case; use the minimum of the host and peer
         * intervals, but not less than minpoll. In other words,
         * oversampling is okay but understampling is evil.
         */
        } else {
                peer->nextdate = peer->outdate +
                    RANDPOLL(max(min(peer->ppoll, hpoll),
                    peer->minpoll));
        }

        /*
         * If the time for the next poll has already happened, bring it
         * up to the next second after this one. This way the only way
         * to get nexdate == current time is from the poll routine.
         */
        if (peer->nextdate <= current_time)
                peer->nextdate = current_time + 1;
#ifdef DEBUG
        if (debug > 1)
                printf("poll_update: at %lu %s flags %04x poll %d burst %d last %lu next %lu\n",
                    current_time, ntoa(&peer->srcadr), peer->flags,
                    peer->hpoll, peer->burst, peer->outdate,
                    peer->nextdate);
#endif
}

/*
 * peer_crypto_clear - discard crypto information
 */
void
peer_crypto_clear(
                  struct peer *peer
                  )
{
        /*
         * If cryptographic credentials have been acquired, toss them to
         * Valhalla. Note that autokeys are ephemeral, in that they are
         * tossed immediately upon use. Therefore, the keylist can be
         * purged anytime without needing to preserve random keys. Note
         * that, if the peer is purged, the cryptographic variables are
         * purged, too. This makes it much harder to sneak in some
         * unauthenticated data in the clock filter.
         */
        DPRINTF(1, ("peer_crypto_clear: at %ld next %ld assoc ID %d\n",
                    current_time, peer->nextdate, peer->associd));

#ifdef OPENSSL
        peer->assoc = 0;
        peer->crypto = 0;

        if (peer->pkey != NULL)
                EVP_PKEY_free(peer->pkey);
        peer->pkey = NULL;

        peer->digest = NULL;    /* XXX MEMLEAK? check whether this needs to be freed in any way - never was freed */

        if (peer->subject != NULL)
                free(peer->subject);
        peer->subject = NULL;

        if (peer->issuer != NULL)
                free(peer->issuer);
        peer->issuer = NULL;

        peer->pkeyid = 0;

        peer->pcookie = 0;

        if (peer->ident_pkey != NULL)
                EVP_PKEY_free(peer->ident_pkey);
        peer->ident_pkey = NULL;
        
        memset(&peer->fstamp, 0, sizeof(peer->fstamp));

        if (peer->iffval != NULL)
                BN_free(peer->iffval);
        peer->iffval = NULL;

        if (peer->grpkey != NULL)
                BN_free(peer->grpkey);
        peer->grpkey = NULL;

        value_free(&peer->cookval);
        value_free(&peer->recval);

        if (peer->cmmd != NULL) {
                free(peer->cmmd);
                peer->cmmd = NULL;
        }

        key_expire(peer);

        value_free(&peer->encrypt);
#endif /* OPENSSL */
}

/*
 * peer_clear - clear peer filter registers.  See Section 3.4.8 of the spec.
 */
void
peer_clear(
        struct peer *peer,              /* peer structure */
        char    *ident                  /* tally lights */
        )
{
        int     i;

        peer_crypto_clear(peer);
        
        if (peer == sys_peer)
                sys_peer = NULL;

        /*
         * Wipe the association clean and initialize the nonzero values.
         */
        memset(CLEAR_TO_ZERO(peer), 0, LEN_CLEAR_TO_ZERO);
        peer->estbdelay = sys_bdelay;
        peer->ppoll = peer->maxpoll;
        peer->hpoll = peer->minpoll;
        peer->disp = MAXDISPERSE;
        peer->jitter = LOGTOD(sys_precision);
        for (i = 0; i < NTP_SHIFT; i++) {
                peer->filter_order[i] = i;
                peer->filter_disp[i] = MAXDISPERSE;
        }
#ifdef REFCLOCK
        if (!(peer->flags & FLAG_REFCLOCK)) {
                peer->leap = LEAP_NOTINSYNC;
                peer->stratum = STRATUM_UNSPEC;
                memcpy(&peer->refid, ident, 4);
        }
#else
        peer->leap = LEAP_NOTINSYNC;
        peer->stratum = STRATUM_UNSPEC;
        memcpy(&peer->refid, ident, 4);
#endif /* REFCLOCK */

        /*
         * During initialization use the association count to spread out
         * the polls at one-second intervals. Othersie, randomize over
         * the minimum poll interval in order to avoid broadcast
         * implosion.
         */
        peer->nextdate = peer->update = peer->outdate = current_time;
        if (initializing)
                peer->nextdate += peer_associations;
        else if (peer->hmode == MODE_PASSIVE)
                peer->nextdate += RESP_DELAY;
        else
                peer->nextdate += (ntp_random() & ((1 << NTP_MINDPOLL) -
                    1));

        DPRINTF(1, ("peer_clear: at %ld next %ld assoc ID %d refid %s\n",
                    current_time, peer->nextdate, peer->associd, ident));
}


/*
 * clock_filter - add incoming clock sample to filter register and run
 *                the filter procedure to find the best sample.
 */
void
clock_filter(
        struct peer *peer,              /* peer structure pointer */
        double  sample_offset,          /* clock offset */
        double  sample_delay,           /* roundtrip delay */
        double  sample_disp             /* dispersion */
        )
{
        double  dst[NTP_SHIFT];         /* distance vector */
        int     ord[NTP_SHIFT];         /* index vector */
        int     i, j, k, m;
        double  dtemp, etemp;

        /*
         * Shift the new sample into the register and discard the oldest
         * one. The new offset and delay come directly from the
         * timestamp calculations. The dispersion grows from the last
         * outbound packet or reference clock update to the present time
         * and increased by the sum of the peer precision and the system
         * precision. The delay can sometimes swing negative due to
         * frequency skew, so it is clamped non-negative.
         */
        j = peer->filter_nextpt;
        peer->filter_offset[j] = sample_offset;
        peer->filter_delay[j] = max(0, sample_delay);
        peer->filter_disp[j] = sample_disp;
        peer->filter_epoch[j] = current_time;
        j = (j + 1) % NTP_SHIFT;
        peer->filter_nextpt = j;

        /*
         * Update dispersions since the last update and at the same
         * time initialize the distance and index lists. The distance
         * list uses a compound metric. If the sample is valid and
         * younger than the minimum Allan intercept, use delay;
         * otherwise, use biased dispersion.
         */
        dtemp = clock_phi * (current_time - peer->update);
        peer->update = current_time;
        for (i = NTP_SHIFT - 1; i >= 0; i--) {
                if (i != 0)
                        peer->filter_disp[j] += dtemp;
                if (peer->filter_disp[j] >= MAXDISPERSE) 
                        peer->filter_disp[j] = MAXDISPERSE;
                if (peer->filter_disp[j] >= MAXDISPERSE)
                        dst[i] = MAXDISPERSE;
                else if (peer->update - peer->filter_epoch[j] >
                    allan_xpt)
                        dst[i] = sys_maxdist + peer->filter_disp[j];
                else
                        dst[i] = peer->filter_delay[j];
                ord[i] = j;
                j++; j %= NTP_SHIFT;
        }

        /*
         * If the clock discipline has stabilized, sort the samples in
         * both lists by distance. Note, we do not displace a higher
         * distance sample by a lower distance one unless lower by at
         * least the precision.  
         */
        if (state == 4) {
                for (i = 1; i < NTP_SHIFT; i++) {
                        for (j = 0; j < i; j++) {
                                if (dst[j] > dst[i] +
                                    LOGTOD(sys_precision)) {
                                        k = ord[j];
                                        ord[j] = ord[i];
                                        ord[i] = k;
                                        etemp = dst[j];
                                        dst[j] = dst[i];
                                        dst[i] = etemp;
                                }
                        }
                }
        }

        /*
         * Copy the index list to the association structure so ntpq
         * can see it later. Prune the distance list to samples less
         * than max distance, but keep at least two valid samples for
         * jitter calculation.
         */
        m = 0;
        for (i = 0; i < NTP_SHIFT; i++) {
                peer->filter_order[i] = (u_char) ord[i];
                if (dst[i] >= MAXDISPERSE || (m >= 2 && dst[i] >=
                    sys_maxdist))
                        continue;
                m++;
        }
        
        /*
         * Compute the dispersion and jitter. The dispersion is weighted
         * exponentially by NTP_FWEIGHT (0.5) so it is normalized close
         * to 1.0. The jitter is the RMS differences relative to the
         * lowest delay sample. If no acceptable samples remain in the
         * shift register, quietly tiptoe home leaving only the
         * dispersion.
         */
        peer->disp = peer->jitter = 0;
        k = ord[0];
        for (i = NTP_SHIFT - 1; i >= 0; i--) {
                j = ord[i];
                peer->disp = NTP_FWEIGHT * (peer->disp +
                    peer->filter_disp[j]);
                if (i < m)
                        peer->jitter += DIFF(peer->filter_offset[j],
                            peer->filter_offset[k]);
        }

        /*
         * If no acceptable samples remain in the shift register,
         * quietly tiptoe home leaving only the dispersion. Otherwise,
         * save the offset, delay and jitter. Note the jitter must not
         * be less than the precision.
         */
        if (m == 0)
                return;

        etemp = fabs(peer->offset - peer->filter_offset[k]);
        peer->offset = peer->filter_offset[k];
        peer->delay = peer->filter_delay[k];
        if (m > 1)
                peer->jitter /= m - 1;
        peer->jitter = max(SQRT(peer->jitter), LOGTOD(sys_precision));

        /*
         * A new sample is useful only if it is younger than the last
         * one used. Note the order is FIFO if the clock discipline has
         * not stabilized.
         */
        if (peer->filter_epoch[k] <= peer->epoch) {
#ifdef DEBUG
                if (debug)
                        printf("clock_filter: discard %lu\n",
                            peer->epoch - peer->filter_epoch[k]);
#endif
                return;
        }

        /*
         * If the difference between the last offset and the current one
         * exceeds the jitter by CLOCK_SGATE and the interval since the
         * last update is less than twice the system poll interval,
         * consider the update a popcorn spike and ignore it.
         */
        if (etemp > CLOCK_SGATE * peer->jitter && m > 1 &&
            peer->filter_epoch[k] - peer->epoch < 2. *
            ULOGTOD(sys_poll)) {
#ifdef DEBUG
                if (debug)
                        printf("clock_filter: popcorn %.6f %.6f\n",
                            etemp, dtemp);
#endif
                return;
        }

        /*
         * The mitigated sample statistics are saved for later
         * processing. If not in a burst, tickle the select.
         */
        peer->epoch = peer->filter_epoch[k];
#ifdef DEBUG
        if (debug)
                printf(
                    "clock_filter: n %d off %.6f del %.6f dsp %.6f jit %.6f, age %lu\n",
                    m, peer->offset, peer->delay, peer->disp,
                    peer->jitter, current_time - peer->epoch);
#endif
        if (peer->burst == 0 || sys_leap == LEAP_NOTINSYNC)
                clock_select();
}


/*
 * clock_select - find the pick-of-the-litter clock
 *
 * LOCKCLOCK: If the local clock is the prefer peer, it will always be
 * enabled, even if declared falseticker, (2) only the prefer peer can
 * be selected as the system peer, (3) if the external source is down,
 * the system leap bits are set to 11 and the stratum set to infinity.
 */
void
clock_select(void)
{
        struct peer *peer;
        int     i, j, k, n;
        int     nlist, nl3;

        int     allow, osurv;
        double  d, e, f, g;
        double  high, low;
        double  synch[NTP_MAXASSOC], error[NTP_MAXASSOC];
        struct peer *osys_peer;
        struct peer *typeacts = NULL;
        struct peer *typelocal = NULL;
        struct peer *typesystem = NULL;

        static int list_alloc = 0;
        static struct endpoint *endpoint = NULL;
        static int *indx = NULL;
        static struct peer **peer_list = NULL;
        static u_int endpoint_size = 0;
        static u_int indx_size = 0;
        static u_int peer_list_size = 0;

        /*
         * Initialize and create endpoint, index and peer lists big
         * enough to handle all associations.
         */
        osys_peer = sys_peer;
        sys_peer = NULL;
        sys_pps = NULL;
        sys_prefer = NULL;
        osurv = sys_survivors;
        sys_survivors = 0;
#ifdef LOCKCLOCK
        sys_leap = LEAP_NOTINSYNC;
        sys_stratum = STRATUM_UNSPEC;
        memcpy(&sys_refid, "DOWN", 4);
#endif /* LOCKCLOCK */
        nlist = 0;
        for (n = 0; n < NTP_HASH_SIZE; n++)
                nlist += peer_hash_count[n];
        if (nlist > list_alloc) {
                if (list_alloc > 0) {
                        free(endpoint);
                        free(indx);
                        free(peer_list);
                }
                while (list_alloc < nlist) {
                        list_alloc += 5;
                        endpoint_size += 5 * 3 * sizeof(*endpoint);
                        indx_size += 5 * 3 * sizeof(*indx);
                        peer_list_size += 5 * sizeof(*peer_list);
                }
                endpoint = (struct endpoint *)emalloc(endpoint_size);
                indx = (int *)emalloc(indx_size);
                peer_list = (struct peer **)emalloc(peer_list_size);
        }

        /*
         * Initially, we populate the island with all the rifraff peers
         * that happen to be lying around. Those with seriously
         * defective clocks are immediately booted off the island. Then,
         * the falsetickers are culled and put to sea. The truechimers
         * remaining are subject to repeated rounds where the most
         * unpopular at each round is kicked off. When the population
         * has dwindled to sys_minclock, the survivors split a million
         * bucks and collectively crank the chimes.
         */
        nlist = nl3 = 0;        /* none yet */
        for (n = 0; n < NTP_HASH_SIZE; n++) {
                for (peer = peer_hash[n]; peer != NULL; peer =
                    peer->next) {
                        peer->flags &= ~FLAG_SYSPEER;
                        peer->status = CTL_PST_SEL_REJECT;

                        /*
                         * Leave the island immediately if the peer is
                         * unfit to synchronize.
                         */
                        if (peer_unfit(peer))
                                continue;

                        /*
                         * Don't allow the local clock or modem drivers
                         * in the kitchen at this point, unless the
                         * prefer peer. Do that later, but only if
                         * nobody else is around. These guys are all
                         * configured, so we never throw them away.
                         */
#ifdef REFCLOCK
                        if (peer->refclktype == REFCLK_LOCALCLOCK
#if defined(VMS) && defined(VMS_LOCALUNIT)
                        /* wjm: VMS_LOCALUNIT taken seriously */
                            && REFCLOCKUNIT(&peer->srcadr) !=
                            VMS_LOCALUNIT
#endif  /* VMS && VMS_LOCALUNIT */
                                ) {
                                typelocal = peer;
#ifndef LOCKCLOCK
                                if (!(peer->flags & FLAG_PREFER))
                                        continue; /* no local clock */
#endif /* LOCKCLOCK */
                        }
                        if (peer->sstclktype == CTL_SST_TS_TELEPHONE) {
                                typeacts = peer;
                                if (!(peer->flags & FLAG_PREFER))
                                        continue; /* no acts */
                        }
#endif /* REFCLOCK */

                        /*
                         * If we get this far, the peer can stay on the
                         * island, but does not yet have the immunity
                         * idol.
                         */
                        peer->status = CTL_PST_SEL_SANE;
                        peer_list[nlist++] = peer;

                        /*
                         * Insert each interval endpoint on the sorted
                         * list.
                         */
                        e = peer->offset;        /* Upper end */
                        f = root_distance(peer);
                        e = e + f;
                        for (i = nl3 - 1; i >= 0; i--) {
                                if (e >= endpoint[indx[i]].val)
                                        break;

                                indx[i + 3] = indx[i];
                        }
                        indx[i + 3] = nl3;
                        endpoint[nl3].type = 1;
                        endpoint[nl3++].val = e;

                        e = e - f;              /* Center point */
                        for (; i >= 0; i--) {
                                if (e >= endpoint[indx[i]].val)
                                        break;

                                indx[i + 2] = indx[i];
                        }
                        indx[i + 2] = nl3;
                        endpoint[nl3].type = 0;
                        endpoint[nl3++].val = e;

                        e = e - f;              /* Lower end */
                        for (; i >= 0; i--) {
                                if (e >= endpoint[indx[i]].val)
                                        break;

                                indx[i + 1] = indx[i];
                        }
                        indx[i + 1] = nl3;
                        endpoint[nl3].type = -1;
                        endpoint[nl3++].val = e;
                }
        }
#ifdef DEBUG
        if (debug > 2)
                for (i = 0; i < nl3; i++)
                        printf("select: endpoint %2d %.6f\n",
                           endpoint[indx[i]].type,
                           endpoint[indx[i]].val);
#endif
        /*
         * This is the actual algorithm that cleaves the truechimers
         * from the falsetickers. The original algorithm was described
         * in Keith Marzullo's dissertation, but has been modified for
         * better accuracy.
         *
         * Briefly put, we first assume there are no falsetickers, then
         * scan the candidate list first from the low end upwards and
         * then from the high end downwards. The scans stop when the
         * number of intersections equals the number of candidates less
         * the number of falsetickers. If this doesn't happen for a
         * given number of falsetickers, we bump the number of
         * falsetickers and try again. If the number of falsetickers
         * becomes equal to or greater than half the number of
         * candidates, the Albanians have won the Byzantine wars and
         * correct synchronization is not possible.
         *
         * Here, nlist is the number of candidates and allow is the
         * number of falsetickers. Upon exit, the truechimers are the
         * susvivors with offsets not less than low and not greater than
         * high. There may be none of them.
         */
        low = 1e9;
        high = -1e9;
        for (allow = 0; 2 * allow < nlist; allow++) {
                int     found;

                /*
                 * Bound the interval (low, high) as the largest
                 * interval containing points from presumed truechimers.
                 */
                found = 0;
                n = 0;
                for (i = 0; i < nl3; i++) {
                        low = endpoint[indx[i]].val;
                        n -= endpoint[indx[i]].type;
                        if (n >= nlist - allow)
                                break;
                        if (endpoint[indx[i]].type == 0)
                                found++;
                }
                n = 0;
                for (j = nl3 - 1; j >= 0; j--) {
                        high = endpoint[indx[j]].val;
                        n += endpoint[indx[j]].type;
                        if (n >= nlist - allow)
                                break;
                        if (endpoint[indx[j]].type == 0)
                                found++;
                }

                /*
                 * If the number of candidates found outside the
                 * interval is greater than the number of falsetickers,
                 * then at least one truechimer is outside the interval,
                 * so go around again. This is what makes this algorithm
                 * different than Marzullo's.
                 */
                if (found > allow)
                        continue;

                /*
                 * If an interval containing truechimers is found, stop.
                 * If not, increase the number of falsetickers and go
                 * around again.
                 */
                if (high > low)
                        break;
        }

        /*
         * Clustering algorithm. Construct candidate list in order first
         * by stratum then by root distance, but keep only the best
         * NTP_MAXASSOC of them. Scan the list to find falsetickers, who
         * leave the island immediately. The TRUE peer is always a
         * truechimer. We must leave at least one peer to collect the
         * million bucks. If in orphan mode, rascals found with lower
         * stratum are guaranteed a seat on the bus.
         */
        j = 0;
        for (i = 0; i < nlist; i++) {
                peer = peer_list[i];
                if (nlist > 1 && (peer->offset <= low || peer->offset >=
                    high) && !(peer->flags & FLAG_TRUE) &&
                    !(sys_stratum >= sys_orphan && peer->stratum <
                    sys_orphan))
                        continue;

                peer->status = CTL_PST_SEL_DISTSYSPEER;

                /*
                 * The order metric is formed from the stratum times
                 * max distance (1.) plus the root distance. It strongly
                 * favors the lowest stratum, but a higher stratum peer
                 * can capture the clock if the low stratum dominant
                 * hasn't been heard for awhile.
                 */
                d = root_distance(peer) + peer->stratum * sys_maxdist;
                if (j >= NTP_MAXASSOC) {
                        if (d >= synch[j - 1])
                                continue;
                        else
                                j--;
                }
                for (k = j; k > 0; k--) {
                        if (d >= synch[k - 1])
                                break;

                        peer_list[k] = peer_list[k - 1];
                        error[k] = error[k - 1];
                        synch[k] = synch[k - 1];
                }
                peer_list[k] = peer;
                error[k] = peer->jitter;
                synch[k] = d;
                j++;
        }
        nlist = j;

        /*
         * If no survivors remain at this point, check if the local
         * clock or modem drivers have been found. If so, nominate one
         * of them as the only survivor. Otherwise, give up and leave
         * the island to the rats.
         */
        if (nlist == 0) {
                if (typeacts != 0) {
                        typeacts->status = CTL_PST_SEL_DISTSYSPEER;
                        peer_list[0] = typeacts;
                        nlist = 1;
                } else if (typelocal != 0) {
                        typelocal->status = CTL_PST_SEL_DISTSYSPEER;
                        peer_list[0] = typelocal;
                        nlist = 1;
                } else {
                        if (osys_peer != NULL) {
                                NLOG(NLOG_SYNCSTATUS)
                                    msyslog(LOG_INFO,
                                    "no servers reachable");
                                report_event(EVNT_PEERSTCHG, NULL);
                        }
                }
        }

        /*
         * We can only trust the survivors if the number of candidates
         * sys_minsane is at least the number required to detect and
         * cast out one falsticker. For the Byzantine agreement
         * algorithm used here, that number is 4; however, the default
         * sys_minsane is 1 to speed initial synchronization. Careful
         * operators will tinker a higher value and use at least that
         * number of synchronization sources.
         */
        if (nlist < sys_minsane)
                return;

        for (i = 0; i < nlist; i++)
                peer_list[i]->status = CTL_PST_SEL_SELCAND;

        /*
         * Now, vote outlyers off the island by select jitter weighted
         * by root distance. Continue voting as long as there are more
         * than sys_minclock survivors and the minimum select jitter is
         * greater than the maximum peer jitter. Stop if we are about to
         * discard a TRUE or PREFER  peer, who of course has the
         * immunity idol.
         */
        while (1) {
                d = 1e9;
                e = -1e9;
                f = g = 0;
                k = 0;
                for (i = 0; i < nlist; i++) {
                        if (error[i] < d)
                                d = error[i];
                        f = 0;
                        if (nlist > 1) {
                                for (j = 0; j < nlist; j++)
                                        f += DIFF(peer_list[j]->offset,
                                            peer_list[i]->offset);
                                f = SQRT(f / (nlist - 1));
                        }
                        if (f * synch[i] > e) {
                                g = f;
                                e = f * synch[i];
                                k = i;
                        }
                }
                f = max(f, LOGTOD(sys_precision));
                if (nlist <= sys_minclock || f <= d ||
                    peer_list[k]->flags & (FLAG_TRUE | FLAG_PREFER))
                        break;
#ifdef DEBUG
                if (debug > 2)
                        printf(
                            "select: drop %s select %.6f jitter %.6f\n",
                            ntoa(&peer_list[k]->srcadr), g, d);
#endif
                for (j = k + 1; j < nlist; j++) {
                        peer_list[j - 1] = peer_list[j];
                        error[j - 1] = error[j];
                }
                nlist--;
        }

        /*
         * What remains is a list usually not greater than sys_minclock
         * peers. We want only a peer at the lowest stratum to become
         * the system peer, although all survivors are eligible for the
         * combining algorithm. Consider each peer in turn and OR the
         * leap bits on the assumption that, if some of them honk
         * nonzero bits, they must know what they are doing. Check for
         * prefer and pps peers at any stratum. Note that the head of
         * the list is at the lowest stratum and that unsynchronized
         * peers cannot survive this far.
         */
        leap_next = 0;
        for (i = 0; i < nlist; i++) {
                peer = peer_list[i];
                sys_survivors++;
                leap_next |= peer->leap;
                peer->status = CTL_PST_SEL_SYNCCAND;
                if (peer->flags & FLAG_PREFER)
                        sys_prefer = peer;
                if (peer == osys_peer)
                        typesystem = peer;
#ifdef REFCLOCK
                if (peer->refclktype == REFCLK_ATOM_PPS)
                        sys_pps = peer;
#endif /* REFCLOCK */
#if DEBUG
                if (debug > 1)
                        printf("cluster: survivor %s metric %.6f\n",
                            ntoa(&peer_list[i]->srcadr), synch[i]);
#endif
        }

        /*
         * Anticlockhop provision. Keep the current system peer if it is
         * a survivor but not first in the list. But do that only HOPPER
         * times.
         */
        if (osys_peer == NULL || typesystem == NULL || typesystem ==
            peer_list[0] || sys_hopper > sys_maxhop) {
                typesystem = peer_list[0];
                sys_hopper = 0;
        } else {
                peer->selbroken++;
        }

        /*
         * Mitigation rules of the game. There are several types of
         * peers that can be selected here: (1) orphan, (2) prefer peer
         * (flag FLAG_PREFER) (3) pps peers (type REFCLK_ATOM_PPS), (4)
         * the existing system peer, if any, and (5) the head of the
         * survivor list.
         */
        if (typesystem->stratum >= sys_orphan) {

                /*
                 * If in orphan mode, choose the system peer. If the
                 * lowest distance, we are the orphan parent and the
                 * offset is zero.
                 */
                sys_peer = typesystem;
                sys_peer->status = CTL_PST_SEL_SYSPEER;
                if (sys_orphandelay < sys_peer->rootdelay) {
                        sys_offset = 0;
                        sys_refid = htonl(LOOPBACKADR);
                } else {
                        sys_offset = sys_peer->offset;
                        sys_refid = addr2refid(&sys_peer->srcadr);
                }
                sys_jitter = LOGTOD(sys_precision);
#ifdef DEBUG
                if (debug > 1)
                        printf("select: orphan offset %.6f\n",
                            sys_offset);
#endif
        } else if (sys_prefer) {

                /*
                 * If a pps peer is present, choose it; otherwise,
                 * choose the prefer peer.
                 */
                if (sys_pps) {
                        sys_peer = sys_pps;
                        sys_peer->status = CTL_PST_SEL_PPS;
                        sys_offset = sys_peer->offset;
                        if (!pps_control)
                                NLOG(NLOG_SYSEVENT)
                                    msyslog(LOG_INFO,
                                    "pps sync enabled");
                        pps_control = current_time;
#ifdef DEBUG
                        if (debug > 1)
                                printf("select: pps offset %.6f\n",
                                    sys_offset);
#endif
                } else {
                        sys_peer = sys_prefer;
                        sys_peer->status = CTL_PST_SEL_SYSPEER;
                        sys_offset = sys_peer->offset;
#ifdef DEBUG
                        if (debug > 1)
                                printf("select: prefer offset %.6f\n",
                                    sys_offset);
#endif
                }
                if (sys_peer->stratum == STRATUM_REFCLOCK ||
                    sys_peer->stratum == STRATUM_UNSPEC)
                        sys_refid = sys_peer->refid;
                else
                        sys_refid = addr2refid(&sys_peer->srcadr);
                sys_jitter = sys_peer->jitter;
        } else {

                /*
                 * Otherwise, choose the anticlockhopper.
                 */ 
                sys_peer = typesystem;
                sys_peer->status = CTL_PST_SEL_SYSPEER;
                clock_combine(peer_list, nlist);
                if (sys_peer->stratum == STRATUM_REFCLOCK ||
                    sys_peer->stratum == STRATUM_UNSPEC)
                        sys_refid = sys_peer->refid;
                else
                        sys_refid = addr2refid(&sys_peer->srcadr);
                sys_jitter = SQRT(SQUARE(sys_peer->jitter) +
                    SQUARE(sys_jitter));
#ifdef DEBUG
                if (debug > 1)
                        printf("select: combine offset %.6f\n",
                           sys_offset);
#endif
        }

        /*
         * We have found the alpha male.
         */
        sys_peer->flags |= FLAG_SYSPEER;
        if (osys_peer != sys_peer) {
                char *src;

                report_event(EVNT_PEERSTCHG, NULL);

#ifdef REFCLOCK
                if (sys_peer->flags & FLAG_REFCLOCK)
                        src = refnumtoa(&sys_peer->srcadr);
                else
#endif /* REFCLOCK */
                        src = ntoa(&sys_peer->srcadr);
                NLOG(NLOG_SYNCSTATUS)
                    msyslog(LOG_INFO, "synchronized to %s, stratum %d",
                        src, sys_peer->stratum);
        }
        clock_update();
}


/*
 * clock_combine - compute system offset and jitter from selected peers
 */
static void
clock_combine(
        struct peer **peers,            /* survivor list */
        int     npeers                  /* number of survivors */
        )
{
        int     i;
        double  x, y, z, w;

        y = z = w = 0;
        for (i = 0; i < npeers; i++) {
                x = root_distance(peers[i]);
                y += 1. / x;
                z += peers[i]->offset / x;
                w += SQUARE(peers[i]->offset - peers[0]->offset) / x;
        }
        sys_offset = z / y;
        sys_jitter = SQRT(w / y);
}

/*
 * root_distance - compute synchronization distance from peer to root
 */
static double
root_distance(
        struct peer *peer
        )
{
        double  dist;

        /*
         * Careful squeak here. The value returned must be greater than
         * the minimum root dispersion in order to avoid clockhop with
         * highly precise reference clocks. In orphan mode lose the peer
         * root delay, as that is used by the election algorithm.
         */
        if (peer->stratum >= sys_orphan)
                dist = 0;
        else
                dist = peer->rootdelay;
        dist += max(sys_mindisp, dist + peer->delay) / 2 +
            peer->rootdispersion + peer->disp + clock_phi *
            (current_time - peer->update) + peer->jitter;
        return (dist);
}

/*
 * peer_xmit - send packet for persistent association.
 */
static void
peer_xmit(
        struct peer *peer       /* peer structure pointer */
        )
{
        struct pkt xpkt;        /* transmit packet */
        int     sendlen, authlen;
        keyid_t xkeyid = 0;     /* transmit key ID */
        l_fp    xmt_tx;

        if (!peer->dstadr)      /* don't bother with peers without interface */
                return;

        /*
         * This is deliciously complicated. There are three cases.
         *
         * case         leap    stratum refid   delay   dispersion
         *
         * normal       system  system  system  system  system
         * orphan child 00      orphan  system  orphan  system
         * orphan parent 00     orphan  loopbk  0       0
         */
        /*
         * This is a normal packet. Use the system variables.
         */
        if (sys_stratum < sys_orphan) {
                xpkt.li_vn_mode = PKT_LI_VN_MODE(sys_leap,
                    peer->version, peer->hmode);
                xpkt.stratum = STRATUM_TO_PKT(sys_stratum);
                xpkt.refid = sys_refid;
                xpkt.rootdelay = HTONS_FP(DTOFP(sys_rootdelay));
                xpkt.rootdispersion =
                    HTONS_FP(DTOUFP(sys_rootdispersion));

        /*
         * This is a orphan child packet. The host is synchronized to an
         * orphan parent. Show leap synchronized, orphan stratum, system
         * reference ID, orphan root delay and system root dispersion.
         */
        } else if (sys_peer != NULL) {
                xpkt.li_vn_mode = PKT_LI_VN_MODE(LEAP_NOWARNING,
                    peer->version, peer->hmode);
                xpkt.stratum = STRATUM_TO_PKT(sys_orphan);
                xpkt.refid = htonl(LOOPBACKADR);
                xpkt.rootdelay = HTONS_FP(DTOFP(sys_orphandelay));
                xpkt.rootdispersion =
                    HTONS_FP(DTOUFP(sys_rootdispersion));

        /*
         * This is an orphan parent. Show leap synchronized, orphan
         * stratum, loopack reference ID and zero root delay and root
         * dispersion.
         */
        } else {
                xpkt.li_vn_mode = PKT_LI_VN_MODE(LEAP_NOWARNING,
                    peer->version, peer->hmode);
                xpkt.stratum = STRATUM_TO_PKT(sys_orphan);
                xpkt.refid = sys_refid;
                xpkt.rootdelay = 0;
                xpkt.rootdispersion = 0;
        }
        xpkt.ppoll = peer->hpoll;
        xpkt.precision = sys_precision;
        HTONL_FP(&sys_reftime, &xpkt.reftime);
        HTONL_FP(&peer->org, &xpkt.org);
        HTONL_FP(&peer->rec, &xpkt.rec);

        /*
         * If the received packet contains a MAC, the transmitted packet
         * is authenticated and contains a MAC. If not, the transmitted
         * packet is not authenticated.
         *
         * It is most important when autokey is in use that the local
         * interface IP address be known before the first packet is
         * sent. Otherwise, it is not possible to compute a correct MAC
         * the recipient will accept. Thus, the I/O semantics have to do
         * a little more work. In particular, the wildcard interface
         * might not be usable.
         */
        sendlen = LEN_PKT_NOMAC;
        if (!(peer->flags & FLAG_AUTHENABLE)) {
                get_systime(&peer->xmt);
                HTONL_FP(&peer->xmt, &xpkt.xmt);
                sendpkt(&peer->srcadr, peer->dstadr, sys_ttl[peer->ttl],
                        &xpkt, sendlen);
                peer->sent++;
#ifdef DEBUG
                if (debug)
                        printf("transmit: at %ld %s->%s mode %d\n",
                               current_time, peer->dstadr ? stoa(&peer->dstadr->sin) : "-",
                               stoa(&peer->srcadr), peer->hmode);
#endif
                return;
        }

        /*
         * The received packet contains a MAC, so the transmitted packet
         * must be authenticated. If autokey is enabled, fuss with the
         * various modes; otherwise, symmetric key cryptography is used.
         */
#ifdef OPENSSL
        if (crypto_flags && (peer->flags & FLAG_SKEY)) {
                struct exten *exten;    /* extension field */

                /*
                 * The Public Key Dance (PKD): Cryptographic credentials
                 * are contained in extension fields, each including a
                 * 4-octet length/code word followed by a 4-octet
                 * association ID and optional additional data. Optional
                 * data includes a 4-octet data length field followed by
                 * the data itself. Request messages are sent from a
                 * configured association; response messages can be sent
                 * from a configured association or can take the fast
                 * path without ever matching an association. Response
                 * messages have the same code as the request, but have
                 * a response bit and possibly an error bit set. In this
                 * implementation, a message may contain no more than
                 * one command and no more than one response.
                 *
                 * Cryptographic session keys include both a public and
                 * a private componet. Request and response messages
                 * using extension fields are always sent with the
                 * private component set to zero. Packets without
                 * extension fields indlude the private component when
                 * the session key is generated.
                 */
                while (1) {
                
                        /*
                         * Allocate and initialize a keylist if not
                         * already done. Then, use the list in inverse
                         * order, discarding keys once used. Keep the
                         * latest key around until the next one, so
                         * clients can use client/server packets to
                         * compute propagation delay.
                         *
                         * Note that once a key is used from the list,
                         * it is retained in the key cache until the
                         * next key is used. This is to allow a client
                         * to retrieve the encrypted session key
                         * identifier to verify authenticity.
                         *
                         * If for some reason a key is no longer in the
                         * key cache, a birthday has happened and the
                         * pseudo-random sequence is probably broken. In
                         * that case, purge the keylist and regenerate
                         * it.
                         */
                        if (peer->keynumber == 0)
                                make_keylist(peer, peer->dstadr);
                        else
                                peer->keynumber--;
                        xkeyid = peer->keylist[peer->keynumber];
                        if (authistrusted(xkeyid))
                                break;
                        else
                                key_expire(peer);
                }
                peer->keyid = xkeyid;
                exten = NULL;
                switch (peer->hmode) {

                        /*
                         * In broadcast server mode the autokey values are
                         * required by the broadcast clients. Push them when a
                         * new keylist is generated; otherwise, push the
                         * association message so the client can request them at
                         * other times.
                         */
                case MODE_BROADCAST:
                        if (peer->flags & FLAG_ASSOC)
                                exten = crypto_args(peer, CRYPTO_AUTO |
                                                    CRYPTO_RESP, NULL);
                        else
                                exten = crypto_args(peer, CRYPTO_ASSOC |
                                                    CRYPTO_RESP, NULL);
                        break;

                /*
                 * In symmetric modes the digest, certificate, agreement
                 * parameters, cookie and autokey values are required.
                 * The leapsecond table is optional. But, a passive peer
                 * will not believe the active peer until the latter has
                 * synchronized, so the agreement must be postponed
                 * until then. In any case, if a new keylist is
                 * generated, the autokey values are pushed.
                 *
                 * If the crypto bit is lit, don't send requests.
                 */
                case MODE_ACTIVE:
                case MODE_PASSIVE:
                        if (peer->flash & TEST9)
                                break;
                        /*
                         * Parameter and certificate.
                         */
                        if (!peer->crypto)
                                exten = crypto_args(peer, CRYPTO_ASSOC,
                                                    sys_hostname);
                        else if (!(peer->crypto & CRYPTO_FLAG_VALID))
                                exten = crypto_args(peer, CRYPTO_CERT,
                                                    peer->issuer);

                        /*
                         * Identity. Note we have to sign the
                         * certificate before the cookie to avoid a
                         * deadlock when the passive peer is walking the
                         * certificate trail. Awesome.
                         */
                        else if (!(peer->crypto & CRYPTO_FLAG_VRFY))
                                exten = crypto_args(peer,
                                                    crypto_ident(peer), NULL);
                        else if (sys_leap != LEAP_NOTINSYNC &&
                                 !(peer->crypto & CRYPTO_FLAG_SIGN))
                                exten = crypto_args(peer, CRYPTO_SIGN,
                                                    sys_hostname);

                        /*
                         * Autokey. We request the cookie only when the
                         * server and client are synchronized and
                         * signatures work both ways. On the other hand,
                         * the active peer needs the autokey values
                         * before then and when the passive peer is
                         * waiting for the active peer to synchronize.
                         * Any time we regenerate the key list, we offer
                         * the autokey values without being asked.
                         */
                        else if (sys_leap != LEAP_NOTINSYNC &&
                                 peer->leap != LEAP_NOTINSYNC &&
                                 !(peer->crypto & CRYPTO_FLAG_AGREE))
                                exten = crypto_args(peer, CRYPTO_COOK,
                                                    NULL);
                        else if (peer->flags & FLAG_ASSOC)
                                exten = crypto_args(peer, CRYPTO_AUTO |
                                                    CRYPTO_RESP, NULL);
                        else if (!(peer->crypto & CRYPTO_FLAG_AUTO))
                                exten = crypto_args(peer, CRYPTO_AUTO,
                                                    NULL);

                        /*
                         * Postamble. We trade leapseconds only when the
                         * server and client are synchronized.
                         */
                        else if (sys_leap != LEAP_NOTINSYNC &&
                                 peer->leap != LEAP_NOTINSYNC &&
                                 peer->crypto & CRYPTO_FLAG_TAI &&
                                 !(peer->crypto & CRYPTO_FLAG_LEAP))
                                exten = crypto_args(peer, CRYPTO_TAI,
                                                    NULL);
                        break;

                /*
                 * In client mode the digest, certificate, agreement
                 * parameters and cookie are required. The leapsecond
                 * table is optional. If broadcast client mode, the
                 * autokey values are required as well. In broadcast
                 * client mode, these values must be acquired during the
                 * client/server exchange to avoid having to wait until
                 * the next key list regeneration. Otherwise, the poor
                 * dude may die a lingering death until becoming
                 * unreachable and attempting rebirth.
                 *
                 * If neither the server or client have the agreement
                 * parameters, the protocol transmits the cookie in the
                 * clear. If the server has the parameters, the client
                 * requests them and the protocol blinds it using the
                 * agreed key. It is a protocol error if the client has
                 * the parameters but the server does not.
                 *
                 * If the crypto bit is lit, don't send requests.
                 */
                case MODE_CLIENT:
                        if (peer->flash & TEST9)
                                break;
                        /*
                         * Parameter and certificate.
                         */
                        if (!peer->crypto)
                                exten = crypto_args(peer, CRYPTO_ASSOC,
                                                    sys_hostname);
                        else if (!(peer->crypto & CRYPTO_FLAG_VALID))
                                exten = crypto_args(peer, CRYPTO_CERT,
                                                    peer->issuer);

                        /*
                         * Identity
                         */
                        else if (!(peer->crypto & CRYPTO_FLAG_VRFY))
                                exten = crypto_args(peer,
                                                    crypto_ident(peer), NULL);

                        /*
                         * Autokey
                         */
                        else if (!(peer->crypto & CRYPTO_FLAG_AGREE))
                                exten = crypto_args(peer, CRYPTO_COOK,
                                                    NULL);
                        else if (!(peer->crypto & CRYPTO_FLAG_AUTO) &&
                                 (peer->cast_flags & MDF_BCLNT))
                                exten = crypto_args(peer, CRYPTO_AUTO,
                                                    NULL);

                        /*
                         * Postamble. We can sign the certificate here,
                         * since there is no chance of deadlock.
                         */
                        else if (sys_leap != LEAP_NOTINSYNC &&
                                 !(peer->crypto & CRYPTO_FLAG_SIGN))
                                exten = crypto_args(peer, CRYPTO_SIGN,
                                                    sys_hostname);
                        else if (sys_leap != LEAP_NOTINSYNC &&
                                 peer->crypto & CRYPTO_FLAG_TAI &&
                                 !(peer->crypto & CRYPTO_FLAG_LEAP))
                                exten = crypto_args(peer, CRYPTO_TAI,
                                                    NULL);
                        break;
                }

                /*
                 * Build the extension fields as directed. A response to
                 * a request is always sent, even if an error. If an
                 * error occurs when sending a request, the crypto
                 * machinery broke or was misconfigured. In that case
                 * light the crypto bit to suppress further requests.
                 */
                if (peer->cmmd != NULL) {
                        peer->cmmd->associd = htonl(peer->associd);
                        sendlen += crypto_xmit(&xpkt, &peer->srcadr,
                                               sendlen, peer->cmmd, 0);
                        free(peer->cmmd);
                        peer->cmmd = NULL;
                }
                if (exten != NULL) {
                        int ltemp = 0;

                        if (exten->opcode != 0) {
                                ltemp = crypto_xmit(&xpkt,
                                                       &peer->srcadr, sendlen, exten, 0);
                                if (ltemp == 0) {
                                        peer->flash |= TEST9; /* crypto error */
                                        free(exten);
                                        return;
                                }
                        }
                        sendlen += ltemp;
                        free(exten);
                }

                /*
                 * If extension fields are present, we must use a
                 * private cookie value of zero. Don't send if the
                 * crypto bit is set and no extension field is present,
                 * but in that case give back the key. Most intricate.
                 */
                if (sendlen > LEN_PKT_NOMAC) {
                        session_key(&peer->dstadr->sin, &peer->srcadr,
                            xkeyid, 0, 2);
                } else if (peer->flash & TEST9) {
                        authtrust(xkeyid, 0);
                        return;
                }
        } 
#endif /* OPENSSL */

        /*
         * Stash the transmit timestamp corrected for the encryption
         * delay. If autokey, give back the key, as we use keys only
         * once. Check for errors such as missing keys, buffer overflow,
         * etc.
         */
        xkeyid = peer->keyid;
        get_systime(&peer->xmt);
        L_ADD(&peer->xmt, &sys_authdelay);
        HTONL_FP(&peer->xmt, &xpkt.xmt);
        authlen = authencrypt(xkeyid, (u_int32 *)&xpkt, sendlen);
        if (authlen == 0) {
                msyslog(LOG_INFO, "transmit: %s key %u not found",
                    stoa(&peer->srcadr), xkeyid);
                peer->flash |= TEST9;           /* no key found */
                return;
        }
        sendlen += authlen;
#ifdef OPENSSL
        if (xkeyid > NTP_MAXKEY)
                authtrust(xkeyid, 0);
#endif /* OPENSSL */
        get_systime(&xmt_tx);
        if (sendlen > sizeof(xpkt)) {
                msyslog(LOG_ERR, "buffer overflow %u", sendlen);
                exit (-1);
        }
        sendpkt(&peer->srcadr, peer->dstadr, sys_ttl[peer->ttl], &xpkt,
                sendlen);

        /*
         * Calculate the encryption delay. Keep the minimum over
         * the latest two samples.
         */
        L_SUB(&xmt_tx, &peer->xmt);
        L_ADD(&xmt_tx, &sys_authdelay);
        sys_authdly[1] = sys_authdly[0];
        sys_authdly[0] = xmt_tx.l_uf;
        if (sys_authdly[0] < sys_authdly[1])
                sys_authdelay.l_uf = sys_authdly[0];
        else
                sys_authdelay.l_uf = sys_authdly[1];
        peer->sent++;
#ifdef OPENSSL
#ifdef DEBUG
        if (debug)
                printf(
                        "transmit: at %ld %s->%s mode %d keyid %08x len %d mac %d index %d\n",
                        current_time, peer->dstadr ? ntoa(&peer->dstadr->sin) : "-",
                        ntoa(&peer->srcadr), peer->hmode, xkeyid, sendlen -
                        authlen, authlen, peer->keynumber);
#endif
#else
#ifdef DEBUG
        if (debug)
                printf(
                        "transmit: at %ld %s->%s mode %d keyid %08x len %d mac %d\n",
                        current_time, peer->dstadr ? ntoa(&peer->dstadr->sin) : "-",
                        ntoa(&peer->srcadr), peer->hmode, xkeyid, sendlen -
                        authlen, authlen);
#endif
#endif /* OPENSSL */
}


/*
 * fast_xmit - Send packet for nonpersistent association. Note that
 * neither the source or destination can be a broadcast address.
 */
static void
fast_xmit(
        struct recvbuf *rbufp,  /* receive packet pointer */
        int     xmode,          /* transmit mode */
        keyid_t xkeyid,         /* transmit key ID */
        int     mask            /* restrict mask */
        )
{
        struct pkt xpkt;                /* transmit packet structure */
        struct pkt *rpkt;               /* receive packet structure */
        l_fp    xmt_ts;                 /* timestamp */
        l_fp    xmt_tx;                 /* timestamp after authent */
        int     sendlen, authlen;
#ifdef OPENSSL
        u_int32 temp32;
#endif

        /*
         * Initialize transmit packet header fields from the receive
         * buffer provided. We leave some fields intact as received. If
         * the gazinta was from a multicast address, the gazoutta must
         * go out another way.
         *
         * The root delay field is special. If the system stratum is
         * less than the orphan stratum, send the real root delay.
         * Otherwise, if there is no system peer, send the orphan delay.
         * Otherwise, we must be an orphan parent, so send zero.
         */
        rpkt = &rbufp->recv_pkt;
        if (rbufp->dstadr->flags & INT_MCASTOPEN)
                rbufp->dstadr = findinterface(&rbufp->recv_srcadr);

        /*
         * This is deliciously complicated. There are four cases.
         *
         * case         leap    stratum refid   delay   dispersion
         *
         * KoD          11      16      KISS    system  system
         * normal       system  system  system  system  system
         * orphan child 00      orphan  system  orphan  system
         * orphan parent 00     orphan  loopbk  0       0
         */
        /*
         * This is a kiss-of-death (KoD) packet. Show leap
         * unsynchronized, stratum zero, reference ID the four-character
         * kiss code and system root delay. Note the rate limit on these
         * packets. Once a second initialize a bucket counter. Every
         * packet sent decrements the counter until reaching zero. If
         * the counter is zero, drop the kiss.
         */
        if (mask & RES_LIMITED) {
                sys_limitrejected++;
                if (sys_kod == 0 || !(mask & RES_DEMOBILIZE))
                        return;

                sys_kod--;
                xpkt.li_vn_mode = PKT_LI_VN_MODE(LEAP_NOTINSYNC,
                    PKT_VERSION(rpkt->li_vn_mode), xmode);
                xpkt.stratum = STRATUM_UNSPEC;
                memcpy(&xpkt.refid, "RATE", 4);
                xpkt.rootdelay = HTONS_FP(DTOFP(sys_rootdelay));
                xpkt.rootdispersion =
                    HTONS_FP(DTOUFP(sys_rootdispersion));

        /*
         * This is a normal packet. Use the system variables.
         */
        } else if (sys_stratum < sys_orphan) {
                xpkt.li_vn_mode = PKT_LI_VN_MODE(sys_leap,
                    PKT_VERSION(rpkt->li_vn_mode), xmode);
                xpkt.stratum = STRATUM_TO_PKT(sys_stratum);
                xpkt.refid = sys_refid;
                xpkt.rootdelay = HTONS_FP(DTOFP(sys_rootdelay));
                xpkt.rootdispersion =
                    HTONS_FP(DTOUFP(sys_rootdispersion));

        /*
         * This is a orphan child packet. The host is synchronized to an
         * orphan parent. Show leap synchronized, orphan stratum, system
         * reference ID and orphan root delay.
         */
        } else if (sys_peer != NULL) {
                xpkt.li_vn_mode = PKT_LI_VN_MODE(LEAP_NOWARNING,
                    PKT_VERSION(rpkt->li_vn_mode), xmode);
                xpkt.stratum = STRATUM_TO_PKT(sys_orphan);
                xpkt.refid = sys_refid;
                xpkt.rootdelay = HTONS_FP(DTOFP(sys_orphandelay));
                xpkt.rootdispersion =
                    HTONS_FP(DTOUFP(sys_rootdispersion));

        /*
         * This is an orphan parent. Show leap synchronized, orphan
         * stratum, loopack reference ID and zero root delay.
         */
        } else {
                xpkt.li_vn_mode = PKT_LI_VN_MODE(LEAP_NOWARNING,
                    PKT_VERSION(rpkt->li_vn_mode), xmode);
                xpkt.stratum = STRATUM_TO_PKT(sys_orphan);
                xpkt.refid = htonl(LOOPBACKADR);
                xpkt.rootdelay = HTONS_FP(DTOFP(0));
                xpkt.rootdispersion = HTONS_FP(DTOFP(0));
        }
        xpkt.ppoll = rpkt->ppoll;
        xpkt.precision = sys_precision;
        xpkt.rootdispersion = HTONS_FP(DTOUFP(sys_rootdispersion));
        HTONL_FP(&sys_reftime, &xpkt.reftime);
        xpkt.org = rpkt->xmt;
        HTONL_FP(&rbufp->recv_time, &xpkt.rec);

        /*
         * If the received packet contains a MAC, the transmitted packet
         * is authenticated and contains a MAC. If not, the transmitted
         * packet is not authenticated.
         */
        sendlen = LEN_PKT_NOMAC;
        if (rbufp->recv_length == sendlen) {
                get_systime(&xmt_ts);
                HTONL_FP(&xmt_ts, &xpkt.xmt);
                sendpkt(&rbufp->recv_srcadr, rbufp->dstadr, 0, &xpkt,
                    sendlen);
#ifdef DEBUG
                if (debug)
                        printf("transmit: at %ld %s->%s mode %d\n",
                            current_time, stoa(&rbufp->dstadr->sin),
                            stoa(&rbufp->recv_srcadr), xmode);
#endif
                return;
        }

        /*
         * The received packet contains a MAC, so the transmitted packet
         * must be authenticated. For symmetric key cryptography, use
         * the predefined and trusted symmetric keys to generate the
         * cryptosum. For autokey cryptography, use the server private
         * value to generate the cookie, which is unique for every
         * source-destination-key ID combination.
         */
#ifdef OPENSSL
        if (xkeyid > NTP_MAXKEY) {
                keyid_t cookie;

                /*
                 * The only way to get here is a reply to a legitimate
                 * client request message, so the mode must be
                 * MODE_SERVER. If an extension field is present, there
                 * can be only one and that must be a command. Do what
                 * needs, but with private value of zero so the poor
                 * jerk can decode it. If no extension field is present,
                 * use the cookie to generate the session key.
                 */
                cookie = session_key(&rbufp->recv_srcadr,
                    &rbufp->dstadr->sin, 0, sys_private, 0);
                if (rbufp->recv_length >= (int)(sendlen + MAX_MAC_LEN +
                    2 * sizeof(u_int32))) {
                        session_key(&rbufp->dstadr->sin,
                            &rbufp->recv_srcadr, xkeyid, 0, 2);
                        temp32 = CRYPTO_RESP;
                        rpkt->exten[0] |= htonl(temp32);
                        sendlen += crypto_xmit(&xpkt,
                            &rbufp->recv_srcadr, sendlen,
                            (struct exten *)rpkt->exten, cookie);
                } else {
                        session_key(&rbufp->dstadr->sin,
                            &rbufp->recv_srcadr, xkeyid, cookie, 2);
                }
        }
#endif /* OPENSSL */
        get_systime(&xmt_ts);
        L_ADD(&xmt_ts, &sys_authdelay);
        HTONL_FP(&xmt_ts, &xpkt.xmt);
        authlen = authencrypt(xkeyid, (u_int32 *)&xpkt, sendlen);
        sendlen += authlen;
#ifdef OPENSSL
        if (xkeyid > NTP_MAXKEY)
                authtrust(xkeyid, 0);
#endif /* OPENSSL */
        get_systime(&xmt_tx);
        if (sendlen > sizeof(xpkt)) {
                msyslog(LOG_ERR, "buffer overflow %u", sendlen);
                exit (-1);
        }
        sendpkt(&rbufp->recv_srcadr, rbufp->dstadr, 0, &xpkt, sendlen);

        /*
         * Calculate the encryption delay. Keep the minimum over the
         * latest two samples.
         */
        L_SUB(&xmt_tx, &xmt_ts);
        L_ADD(&xmt_tx, &sys_authdelay);
        sys_authdly[1] = sys_authdly[0];
        sys_authdly[0] = xmt_tx.l_uf;
        if (sys_authdly[0] < sys_authdly[1])
                sys_authdelay.l_uf = sys_authdly[0];
        else
                sys_authdelay.l_uf = sys_authdly[1];
#ifdef DEBUG
        if (debug)
                printf(
                    "transmit: at %ld %s->%s mode %d keyid %08x len %d mac %d\n",
                    current_time, ntoa(&rbufp->dstadr->sin),
                    ntoa(&rbufp->recv_srcadr), xmode, xkeyid, sendlen -
                    authlen, authlen);
#endif
}


#ifdef OPENSSL
/*
 * key_expire - purge the key list
 */
void
key_expire(
        struct peer *peer       /* peer structure pointer */
        )
{
        int i;

        if (peer->keylist != NULL) {
                for (i = 0; i <= peer->keynumber; i++)
                        authtrust(peer->keylist[i], 0);
                free(peer->keylist);
                peer->keylist = NULL;
        }
        value_free(&peer->sndval);
        peer->keynumber = 0;
#ifdef DEBUG
        if (debug)
                printf("key_expire: at %lu\n", current_time);
#endif
}
#endif /* OPENSSL */


/*
 * Determine if the peer is unfit for synchronization
 *
 * A peer is unfit for synchronization if
 * > TEST10 bad leap or stratum below floor or at or above ceiling
 * > TEST11 root distance exceeded
 * > TEST12 a direct or indirect synchronization loop would form
 * > TEST13 unreachable or noselect
 */
int                             /* FALSE if fit, TRUE if unfit */
peer_unfit(
        struct peer *peer       /* peer structure pointer */
        )
{
        int     rval = 0;

        /*
         * A stratum error occurs if (1) the server has never been
         * synchronized, (2) the server stratum is below the floor or
         * greater than or equal to the ceiling, (3) the system stratum
         * is below the orphan stratum and the server stratum is greater
         * than or equal to the orphan stratum.
         */
        if (peer->leap == LEAP_NOTINSYNC || peer->stratum < sys_floor ||
            peer->stratum >= sys_ceiling || (sys_stratum < sys_orphan &&
            peer->stratum >= sys_orphan))
                rval |= TEST10;         /* stratum out of bounds */

        /*
         * A distance error occurs if the root distance is greater than
         * or equal to the distance threshold plus the increment due to
         * one poll interval.
         */
        if (root_distance(peer) >= sys_maxdist + clock_phi *
            ULOGTOD(sys_poll))
                rval |= TEST11;         /* distance exceeded */

        /*
         * A loop error occurs if the remote peer is synchronized to the
         * local peer of if the remote peer is synchronized to the same
         * server as the local peer, but only if the remote peer is not
         * the orphan parent.
         */
        if (peer->stratum > 1 && peer->refid != htonl(LOOPBACKADR) &&
            ((!peer->dstadr || peer->refid == peer->dstadr->addr_refid) ||
            peer->refid == sys_refid))
                rval |= TEST12;         /* synch loop */

        /*
         * An unreachable error occurs if the server is unreachable or
         * the noselect bit is set.
         */
        if (!peer->reach || peer->flags & FLAG_NOSELECT)
                rval |= TEST13;         /* unreachable */

        peer->flash &= ~PEER_TEST_MASK;
        peer->flash |= rval;
        return (rval);
}


/*
 * Find the precision of this particular machine
 */
#define MINSTEP 100e-9          /* minimum clock increment (s) */
#define MAXSTEP 20e-3           /* maximum clock increment (s) */
#define MINLOOPS 5              /* minimum number of step samples */

/*
 * This routine calculates the system precision, defined as the minimum
 * of a sequence of differences between successive readings of the
 * system clock. However, if the system clock can be read more than once
 * during a tick interval, the difference can be zero or one LSB unit,
 * where the LSB corresponds to one nanosecond or one microsecond.
 * Conceivably, if some other process preempts this one and reads the
 * clock, the difference can be more than one LSB unit.
 *
 * For hardware clock frequencies of 10 MHz or less, we assume the
 * logical clock advances only at the hardware clock tick. For higher
 * frequencies, we assume the logical clock can advance no more than 100
 * nanoseconds between ticks.
 */
int
default_get_precision(void)
{
        l_fp    val;            /* current seconds fraction */
        l_fp    last;           /* last seconds fraction */
        l_fp    diff;           /* difference */
        double  tick;           /* computed tick value */
        double  dtemp;          /* scratch */
        int     i;              /* log2 precision */

        /*
         * Loop to find tick value in nanoseconds. Toss out outlyer
         * values less than the minimun tick value. In wacky cases, use
         * the default maximum value.
         */
        get_systime(&last);
        tick = MAXSTEP;
        for (i = 0; i < MINLOOPS;) {
                get_systime(&val);
                diff = val;
                L_SUB(&diff, &last);
                last = val;
                LFPTOD(&diff, dtemp);
                if (dtemp < MINSTEP)
                        continue;
                i++;
                if (dtemp < tick)
                        tick = dtemp;
        }

        /*
         * Find the nearest power of two.
         */
        NLOG(NLOG_SYSEVENT)
            msyslog(LOG_INFO, "precision = %.3f usec", tick * 1e6);
        for (i = 0; tick <= 1; i++)
                tick *= 2;
        if (tick - 1. > 1. - tick / 2)
                i--;
        return (-i);
}


/*
 * kod_proto - called once per second to limit kiss-of-death packets
 */
void
kod_proto(void)
{
        sys_kod = sys_kod_rate;
}


/*
 * init_proto - initialize the protocol module's data
 */
void
init_proto(void)
{
        l_fp    dummy;
        int     i;

        /*
         * Fill in the sys_* stuff.  Default is don't listen to
         * broadcasting, authenticate.
         */
        sys_leap = LEAP_NOTINSYNC;
        sys_stratum = STRATUM_UNSPEC;
        memcpy(&sys_refid, "INIT", 4);
        sys_precision = (s_char)default_get_precision();
        sys_jitter = LOGTOD(sys_precision);
        sys_rootdelay = 0;
        sys_orphandelay = (double)(ntp_random() & 0xffff) / 65536. *
            sys_maxdist;
        sys_rootdispersion = 0;
        L_CLR(&sys_reftime);
        sys_peer = NULL;
        sys_survivors = 0;
        get_systime(&dummy);
        sys_manycastserver = 0;
        sys_bclient = 0;
        sys_bdelay = DEFBROADDELAY;
        sys_calldelay = BURST_DELAY;
        sys_authenticate = 1;
        L_CLR(&sys_authdelay);
        sys_authdly[0] = sys_authdly[1] = 0;
        sys_stattime = 0;
        proto_clr_stats();
        for (i = 0; i < MAX_TTL; i++) {
                sys_ttl[i] = (u_char)((i * 256) / MAX_TTL);
                sys_ttlmax = i;
        }
#ifdef OPENSSL
        sys_automax = 1 << NTP_AUTOMAX;
#endif /* OPENSSL */

        /*
         * Default these to enable
         */
        ntp_enable = 1;
#ifndef KERNEL_FLL_BUG
        kern_enable = 1;
#endif
        pps_enable = 0;
        stats_control = 1;
}


/*
 * proto_config - configure the protocol module
 */
void
proto_config(
        int     item,
        u_long  value,
        double  dvalue,
        struct sockaddr_storage* svalue
        )
{
        /*
         * Figure out what he wants to change, then do it
         */
        switch (item) {

        /*
         * Turn on/off kernel discipline.
         */
        case PROTO_KERNEL:
                kern_enable = (int)value;
                break;

        /*
         * Turn on/off clock discipline.
         */
        case PROTO_NTP:
                ntp_enable = (int)value;
                break;

        /*
         * Turn on/off monitoring.
         */
        case PROTO_MONITOR:
                if (value)
                        mon_start(MON_ON);
                else
                        mon_stop(MON_ON);
                break;

        /*
         * Turn on/off statistics.
         */
        case PROTO_FILEGEN:
                stats_control = (int)value;
                break;

        /*
         * Turn on/off enable broadcasts.
         */
        case PROTO_BROADCLIENT:
                sys_bclient = (int)value;
                if (sys_bclient == 0)
                        io_unsetbclient();
                else
                        io_setbclient();
                break;

        /*
         * Turn on/off PPS discipline.
         */
        case PROTO_PPS:
                pps_enable = (int)value;
                break;

        /*
         * Add muliticast group address.
         */
        case PROTO_MULTICAST_ADD:
                if (svalue)
                    io_multicast_add(*svalue);
                sys_bclient = 1;
                break;

        /*
         * Delete multicast group address.
         */
        case PROTO_MULTICAST_DEL:
                if (svalue)
                    io_multicast_del(*svalue);
                break;

        /*
         * Set default broadcast delay.
         */
        case PROTO_BROADDELAY:
                sys_bdelay = dvalue;
                break;

        /*
         * Set modem call delay.
         */
        case PROTO_CALLDELAY:
                sys_calldelay = (int)value;
                break;

        /*
         * Turn on/off authentication to mobilize ephemeral
         * associations.
         */
        case PROTO_AUTHENTICATE:
                sys_authenticate = (int)value;
                break;

        /*
         * Set minimum number of survivors.
         */
        case PROTO_MINCLOCK:
                sys_minclock = (int)dvalue;
                break;

        /*
         * Set maximum number of preemptable associations.
         */
        case PROTO_MAXCLOCK:
                sys_maxclock = (int)dvalue;
                break;

        /*
         * Set minimum number of survivors.
         */
        case PROTO_MINSANE:
                sys_minsane = (int)dvalue;
                break;

        /*
         * Set stratum floor.
         */
        case PROTO_FLOOR:
                sys_floor = (int)dvalue;
                break;

        /*
         * Set stratum ceiling.
         */
        case PROTO_CEILING:
                sys_ceiling = (int)dvalue;
                break;

        /*
         * Set orphan stratum.
         */
        case PROTO_ORPHAN:
                sys_orphan = (int)dvalue;
                break;

        /*
         * Set cohort switch.
         */
        case PROTO_COHORT:
                sys_cohort = (int)dvalue;
                break;

        /*
         * Set minimum dispersion increment.
         */
        case PROTO_MINDISP:
                sys_mindisp = dvalue;
                break;

        /*
         * Set maximum distance (select threshold).
         */
        case PROTO_MAXDIST:
                sys_maxdist = dvalue;
                break;

        /*
         * Set anticlockhop threshold.
         */
        case PROTO_MAXHOP:
                sys_maxhop = (int)dvalue;
                break;

        /*
         * Set adjtime() resolution (s).
         */
        case PROTO_ADJ:
                sys_tick = dvalue;
                break;

        /*
         * Set manycast beacon interval.
         */
        case PROTO_BEACON:
                sys_beacon = (int)dvalue;
                break;

#ifdef REFCLOCK
        /*
         * Turn on/off refclock calibrate
         */
        case PROTO_CAL:
                cal_enable = (int)value;
                break;
#endif /* REFCLOCK */
        default:

                /*
                 * Log this error.
                 */
                msyslog(LOG_INFO,
                    "proto_config: illegal item %d, value %ld", item,
                    value);
        }
}


/*
 * proto_clr_stats - clear protocol stat counters
 */
void
proto_clr_stats(void)
{
        sys_stattime = current_time;
        sys_received = 0;
        sys_processed = 0;
        sys_newversionpkt = 0;
        sys_oldversionpkt = 0;
        sys_unknownversion = 0;
        sys_restricted = 0;
        sys_badlength = 0;
        sys_badauth = 0;
        sys_limitrejected = 0;
}