contrib/bind-9.5.2/lib/isc/include/isc/lfsr.h

   1 /*
   2  * Copyright (C) 2004-2007  Internet Systems Consortium, Inc. ("ISC")
   3  * Copyright (C) 1999-2001  Internet Software Consortium.
   4  *
   5  * Permission to use, copy, modify, and/or distribute this software for any
   6  * purpose with or without fee is hereby granted, provided that the above
   7  * copyright notice and this permission notice appear in all copies.
   8  *
   9  * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
  10  * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
  11  * AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
  12  * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
  13  * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
  14  * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
  15  * PERFORMANCE OF THIS SOFTWARE.
  16  */
  17
  18 /* $Id: lfsr.h,v 1.17 2007/06/19 23:47:18 tbox Exp $ */
  19
  20 #ifndef ISC_LFSR_H
  21 #define ISC_LFSR_H 1
  22
  23 /*! \file isc/lfsr.h */
  24
  25 #include <isc/lang.h>
  26 #include <isc/types.h>
  27
  28 typedef struct isc_lfsr isc_lfsr_t;
  29
  30 /*%
  31  * This function is called when reseeding is needed.  It is allowed to
  32  * modify any state in the LFSR in any way it sees fit OTHER THAN "bits".
  33  *
  34  * It MUST set "count" to a new value or the lfsr will never reseed again.
  35  *
  36  * Also, a reseed will never occur in the middle of an extraction.  This
  37  * is purely an optimization, and is probably what one would want.
  38  */
  39 typedef void (*isc_lfsrreseed_t)(isc_lfsr_t *, void *);
  40
  41 /*%
  42  * The members of this structure can be used by the application, but care
  43  * needs to be taken to not change state once the lfsr is in operation.
  44  */
  45 struct isc_lfsr {
  46         isc_uint32_t            state;  /*%< previous state */
  47         unsigned int            bits;   /*%< length */
  48         isc_uint32_t            tap;    /*%< bit taps */
  49         unsigned int            count;  /*%< reseed count (in BITS!) */
  50         isc_lfsrreseed_t        reseed; /*%< reseed function */
  51         void                   *arg;    /*%< reseed function argument */
  52 };
  53
  54 ISC_LANG_BEGINDECLS
  55
  56
  57 void
  58 isc_lfsr_init(isc_lfsr_t *lfsr, isc_uint32_t state, unsigned int bits,
  59                    isc_uint32_t tap, unsigned int count,
  60                    isc_lfsrreseed_t reseed, void *arg);
  61 /*%<
  62  * Initialize an LFSR.
  63  *
  64  * Note:
  65  *
  66  *\li   Putting untrusted values into this function will cause the LFSR to
  67  *      generate (perhaps) non-maximal length sequences.
  68  *
  69  * Requires:
  70  *
  71  *\li   lfsr != NULL
  72  *
  73  *\li   8 <= bits <= 32
  74  *
  75  *\li   tap != 0
  76  */
  77
  78 void
  79 isc_lfsr_generate(isc_lfsr_t *lfsr, void *data, unsigned int count);
  80 /*%<
  81  * Returns "count" bytes of data from the LFSR.
  82  *
  83  * Requires:
  84  *
  85  *\li   lfsr be valid.
  86  *
  87  *\li   data != NULL.
  88  *
  89  *\li   count > 0.
  90  */
  91
  92 void
  93 isc_lfsr_skip(isc_lfsr_t *lfsr, unsigned int skip);
  94 /*%<
  95  * Skip "skip" states.
  96  *
  97  * Requires:
  98  *
  99  *\li   lfsr be valid.
 100  */
 101
 102 isc_uint32_t
 103 isc_lfsr_generate32(isc_lfsr_t *lfsr1, isc_lfsr_t *lfsr2);
 104 /*%<
 105  * Given two LFSRs, use the current state from each to skip entries in the
 106  * other.  The next states are then xor'd together and returned.
 107  *
 108  * WARNING:
 109  *
 110  *\li   This function is used only for very, very low security data, such
 111  *      as DNS message IDs where it is desired to have an unpredictable
 112  *      stream of bytes that are harder to predict than a simple flooding
 113  *      attack.
 114  *
 115  * Notes:
 116  *
 117  *\li   Since the current state from each of the LFSRs is used to skip
 118  *      state in the other, it is important that no state be leaked
 119  *      from either LFSR.
 120  *
 121  * Requires:
 122  *
 123  *\li   lfsr1 and lfsr2 be valid.
 124  *
 125  *\li   1 <= skipbits <= 31
 126  */
 127
 128 ISC_LANG_ENDDECLS
 129
 130 #endif /* ISC_LFSR_H */