dropbear 2015.71

[tomato.git] / release / src / router / dropbear / keyimport.c

/*
 * Based on PuTTY's import.c for importing/exporting OpenSSH and SSH.com
 * keyfiles.
 *
 * Modifications copyright 2003 Matt Johnston
 *
 * PuTTY is copyright 1997-2003 Simon Tatham.
 * 
 * Portions copyright Robert de Bath, Joris van Rantwijk, Delian
 * Delchev, Andreas Schultz, Jeroen Massar, Wez Furlong, Nicolas Barry,
 * Justin Bradford, and CORE SDI S.A.
 * 
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation files
 * (the "Software"), to deal in the Software without restriction,
 * including without limitation the rights to use, copy, modify, merge,
 * publish, distribute, sublicense, and/or sell copies of the Software,
 * and to permit persons to whom the Software is furnished to do so,
 * subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT.  IN NO EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE
 * FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
 * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

#include "keyimport.h"
#include "bignum.h"
#include "buffer.h"
#include "dbutil.h"
#include "ecc.h"

static const unsigned char OID_SEC256R1_BLOB[] = {0x2a, 0x86, 0x48, 0xce, 0x3d, 0x03, 0x01, 0x07};
static const unsigned char OID_SEC384R1_BLOB[] = {0x2b, 0x81, 0x04, 0x00, 0x22};
static const unsigned char OID_SEC521R1_BLOB[] = {0x2b, 0x81, 0x04, 0x00, 0x23};

#define PUT_32BIT(cp, value) do { \
  (cp)[3] = (unsigned char)(value); \
  (cp)[2] = (unsigned char)((value) >> 8); \
  (cp)[1] = (unsigned char)((value) >> 16); \
  (cp)[0] = (unsigned char)((value) >> 24); } while (0)

#define GET_32BIT(cp) \
        (((unsigned long)(unsigned char)(cp)[0] << 24) | \
        ((unsigned long)(unsigned char)(cp)[1] << 16) | \
        ((unsigned long)(unsigned char)(cp)[2] << 8) | \
        ((unsigned long)(unsigned char)(cp)[3]))

static int openssh_encrypted(const char *filename);
static sign_key *openssh_read(const char *filename, char *passphrase);
static int openssh_write(const char *filename, sign_key *key,
                                  char *passphrase);

static int dropbear_write(const char*filename, sign_key * key);
static sign_key *dropbear_read(const char* filename);

#if 0
static int sshcom_encrypted(const char *filename, char **comment);
static struct ssh2_userkey *sshcom_read(const char *filename, char *passphrase);
static int sshcom_write(const char *filename, struct ssh2_userkey *key,
                                 char *passphrase);
#endif

int import_encrypted(const char* filename, int filetype) {

        if (filetype == KEYFILE_OPENSSH) {
                return openssh_encrypted(filename);
#if 0
        } else if (filetype == KEYFILE_SSHCOM) {
                return sshcom_encrypted(filename, NULL);
#endif
        }
        return 0;
}

sign_key *import_read(const char *filename, char *passphrase, int filetype) {

        if (filetype == KEYFILE_OPENSSH) {
                return openssh_read(filename, passphrase);
        } else if (filetype == KEYFILE_DROPBEAR) {
                return dropbear_read(filename);
#if 0
        } else if (filetype == KEYFILE_SSHCOM) {
                return sshcom_read(filename, passphrase);
#endif
        }
        return NULL;
}

int import_write(const char *filename, sign_key *key, char *passphrase,
                int filetype) {

        if (filetype == KEYFILE_OPENSSH) {
                return openssh_write(filename, key, passphrase);
        } else if (filetype == KEYFILE_DROPBEAR) {
                return dropbear_write(filename, key);
#if 0
        } else if (filetype == KEYFILE_SSHCOM) {
                return sshcom_write(filename, key, passphrase);
#endif
        }
        return 0;
}

static sign_key *dropbear_read(const char* filename) {

        buffer * buf = NULL;
        sign_key *ret = NULL;
        enum signkey_type type;

        buf = buf_new(MAX_PRIVKEY_SIZE);
        if (buf_readfile(buf, filename) == DROPBEAR_FAILURE) {
                goto error;
        }

        buf_setpos(buf, 0);
        ret = new_sign_key();

        type = DROPBEAR_SIGNKEY_ANY;
        if (buf_get_priv_key(buf, ret, &type) == DROPBEAR_FAILURE){
                goto error;
        }
        buf_free(buf);

        ret->type = type;

        return ret;

error:
        if (buf) {
                buf_free(buf);
        }
        if (ret) {
                sign_key_free(ret);
        }
        return NULL;
}

/* returns 0 on fail, 1 on success */
static int dropbear_write(const char*filename, sign_key * key) {

        buffer * buf;
        FILE*fp;
        int len;
        int ret;

        buf = buf_new(MAX_PRIVKEY_SIZE);
        buf_put_priv_key(buf, key, key->type);

        fp = fopen(filename, "w");
        if (!fp) {
                ret = 0;
                goto out;
        }

        buf_setpos(buf, 0);
        do {
                len = fwrite(buf_getptr(buf, buf->len - buf->pos),
                                1, buf->len - buf->pos, fp);
                buf_incrpos(buf, len);
        } while (len > 0 && buf->len != buf->pos);

        fclose(fp);

        if (buf->pos != buf->len) {
                ret = 0;
        } else {
                ret = 1;
        }
out:
        buf_free(buf);
        return ret;
}


/* ----------------------------------------------------------------------
 * Helper routines. (The base64 ones are defined in sshpubk.c.)
 */

#define isbase64(c) (   ((c) >= 'A' && (c) <= 'Z') || \
                                                 ((c) >= 'a' && (c) <= 'z') || \
                                                 ((c) >= '0' && (c) <= '9') || \
                                                 (c) == '+' || (c) == '/' || (c) == '=' \
                                                 )

/* cpl has to be less than 100 */
static void base64_encode_fp(FILE * fp, unsigned char *data,
                int datalen, int cpl)
{
        unsigned char out[100];
    int n;
        unsigned long outlen;
        int rawcpl;
        rawcpl = cpl * 3 / 4;
        dropbear_assert((unsigned int)cpl < sizeof(out));

    while (datalen > 0) {
                n = (datalen < rawcpl ? datalen : rawcpl);
                outlen = sizeof(out);
                base64_encode(data, n, out, &outlen);
                data += n;
                datalen -= n;
                fwrite(out, 1, outlen, fp);
                fputc('\n', fp);
    }
}
/*
 * Read an ASN.1/BER identifier and length pair.
 * 
 * Flags are a combination of the #defines listed below.
 * 
 * Returns -1 if unsuccessful; otherwise returns the number of
 * bytes used out of the source data.
 */

/* ASN.1 tag classes. */
#define ASN1_CLASS_UNIVERSAL            (0 << 6)
#define ASN1_CLASS_APPLICATION    (1 << 6)
#define ASN1_CLASS_CONTEXT_SPECIFIC (2 << 6)
#define ASN1_CLASS_PRIVATE                (3 << 6)
#define ASN1_CLASS_MASK                  (3 << 6)

/* Primitive versus constructed bit. */
#define ASN1_CONSTRUCTED                        (1 << 5)

static int ber_read_id_len(void *source, int sourcelen,
                                                   int *id, int *length, int *flags)
{
        unsigned char *p = (unsigned char *) source;

        if (sourcelen == 0)
                return -1;

        *flags = (*p & 0xE0);
        if ((*p & 0x1F) == 0x1F) {
                *id = 0;
                while (*p & 0x80) {
                        *id = (*id << 7) | (*p & 0x7F);
                        p++, sourcelen--;
                        if (sourcelen == 0)
                                return -1;
                }
                *id = (*id << 7) | (*p & 0x7F);
                p++, sourcelen--;
        } else {
                *id = *p & 0x1F;
                p++, sourcelen--;
        }

        if (sourcelen == 0)
                return -1;

        if (*p & 0x80) {
                int n = *p & 0x7F;
                p++, sourcelen--;
                if (sourcelen < n)
                        return -1;
                *length = 0;
                while (n--)
                        *length = (*length << 8) | (*p++);
                sourcelen -= n;
        } else {
                *length = *p;
                p++, sourcelen--;
        }

        return p - (unsigned char *) source;
}

/*
 * Write an ASN.1/BER identifier and length pair. Returns the
 * number of bytes consumed. Assumes dest contains enough space.
 * Will avoid writing anything if dest is NULL, but still return
 * amount of space required.
 */
static int ber_write_id_len(void *dest, int id, int length, int flags)
{
        unsigned char *d = (unsigned char *)dest;
        int len = 0;

        if (id <= 30) {
                /*
                 * Identifier is one byte.
                 */
                len++;
                if (d) *d++ = id | flags;
        } else {
                int n;
                /*
                 * Identifier is multiple bytes: the first byte is 11111
                 * plus the flags, and subsequent bytes encode the value of
                 * the identifier, 7 bits at a time, with the top bit of
                 * each byte 1 except the last one which is 0.
                 */
                len++;
                if (d) *d++ = 0x1F | flags;
                for (n = 1; (id >> (7*n)) > 0; n++)
                        continue;                                          /* count the bytes */
                while (n--) {
                        len++;
                        if (d) *d++ = (n ? 0x80 : 0) | ((id >> (7*n)) & 0x7F);
                }
        }

        if (length < 128) {
                /*
                 * Length is one byte.
                 */
                len++;
                if (d) *d++ = length;
        } else {
                int n;
                /*
                 * Length is multiple bytes. The first is 0x80 plus the
                 * number of subsequent bytes, and the subsequent bytes
                 * encode the actual length.
                 */
                for (n = 1; (length >> (8*n)) > 0; n++)
                        continue;                                          /* count the bytes */
                len++;
                if (d) *d++ = 0x80 | n;
                while (n--) {
                        len++;
                        if (d) *d++ = (length >> (8*n)) & 0xFF;
                }
        }

        return len;
}


/* Simple structure to point to an mp-int within a blob. */
struct mpint_pos { void *start; int bytes; };

/* ----------------------------------------------------------------------
 * Code to read and write OpenSSH private keys.
 */

enum { OSSH_DSA, OSSH_RSA, OSSH_EC };
struct openssh_key {
        int type;
        int encrypted;
        char iv[32];
        unsigned char *keyblob;
        unsigned int keyblob_len, keyblob_size;
};

static struct openssh_key *load_openssh_key(const char *filename)
{
        struct openssh_key *ret;
        FILE *fp = NULL;
        char buffer[256];
        char *errmsg = NULL, *p = NULL;
        int headers_done;
        unsigned long len, outlen;

        ret = (struct openssh_key*)m_malloc(sizeof(struct openssh_key));
        ret->keyblob = NULL;
        ret->keyblob_len = ret->keyblob_size = 0;
        ret->encrypted = 0;
        memset(ret->iv, 0, sizeof(ret->iv));

        if (strlen(filename) == 1 && filename[0] == '-') {
                fp = stdin;
        } else {
                fp = fopen(filename, "r");
        }
        if (!fp) {
                errmsg = "Unable to open key file";
                goto error;
        }
        if (!fgets(buffer, sizeof(buffer), fp) ||
                0 != strncmp(buffer, "-----BEGIN ", 11) ||
                0 != strcmp(buffer+strlen(buffer)-17, "PRIVATE KEY-----\n")) {
                errmsg = "File does not begin with OpenSSH key header";
                goto error;
        }
        if (!strcmp(buffer, "-----BEGIN RSA PRIVATE KEY-----\n"))
                ret->type = OSSH_RSA;
        else if (!strcmp(buffer, "-----BEGIN DSA PRIVATE KEY-----\n"))
                ret->type = OSSH_DSA;
        else if (!strcmp(buffer, "-----BEGIN EC PRIVATE KEY-----\n"))
                ret->type = OSSH_EC;
        else {
                errmsg = "Unrecognised key type";
                goto error;
        }

        headers_done = 0;
        while (1) {
                if (!fgets(buffer, sizeof(buffer), fp)) {
                        errmsg = "Unexpected end of file";
                        goto error;
                }
                if (0 == strncmp(buffer, "-----END ", 9) &&
                        0 == strcmp(buffer+strlen(buffer)-17, "PRIVATE KEY-----\n"))
                        break;                                     /* done */
                if ((p = strchr(buffer, ':')) != NULL) {
                        if (headers_done) {
                                errmsg = "Header found in body of key data";
                                goto error;
                        }
                        *p++ = '\0';
                        while (*p && isspace((unsigned char)*p)) p++;
                        if (!strcmp(buffer, "Proc-Type")) {
                                if (p[0] != '4' || p[1] != ',') {
                                        errmsg = "Proc-Type is not 4 (only 4 is supported)";
                                        goto error;
                                }
                                p += 2;
                                if (!strcmp(p, "ENCRYPTED\n"))
                                        ret->encrypted = 1;
                        } else if (!strcmp(buffer, "DEK-Info")) {
                                int i, j;

                                if (strncmp(p, "DES-EDE3-CBC,", 13)) {
                                        errmsg = "Ciphers other than DES-EDE3-CBC not supported";
                                        goto error;
                                }
                                p += 13;
                                for (i = 0; i < 8; i++) {
                                        if (1 != sscanf(p, "%2x", &j))
                                                break;
                                        ret->iv[i] = j;
                                        p += 2;
                                }
                                if (i < 8) {
                                        errmsg = "Expected 16-digit iv in DEK-Info";
                                        goto error;
                                }
                        }
                } else {
                        headers_done = 1;
                        len = strlen(buffer);
                        outlen = len*4/3;
                        if (ret->keyblob_len + outlen > ret->keyblob_size) {
                                ret->keyblob_size = ret->keyblob_len + outlen + 256;
                                ret->keyblob = (unsigned char*)m_realloc(ret->keyblob,
                                                ret->keyblob_size);
                        }
                        outlen = ret->keyblob_size - ret->keyblob_len;
                        if (base64_decode((const unsigned char *)buffer, len,
                                                ret->keyblob + ret->keyblob_len, &outlen) != CRYPT_OK){
                                errmsg = "Error decoding base64";
                                goto error;
                        }
                        ret->keyblob_len += outlen;
                }
        }

        if (ret->keyblob_len == 0 || !ret->keyblob) {
                errmsg = "Key body not present";
                goto error;
        }

        if (ret->encrypted && ret->keyblob_len % 8 != 0) {
                errmsg = "Encrypted key blob is not a multiple of cipher block size";
                goto error;
        }

        m_burn(buffer, sizeof(buffer));
        return ret;

        error:
        m_burn(buffer, sizeof(buffer));
        if (ret) {
                if (ret->keyblob) {
                        m_burn(ret->keyblob, ret->keyblob_size);
                        m_free(ret->keyblob);
                }
                m_free(ret);
        }
        if (fp) {
                fclose(fp);
        }
        if (errmsg) {
                fprintf(stderr, "Error: %s\n", errmsg);
        }
        return NULL;
}

static int openssh_encrypted(const char *filename)
{
        struct openssh_key *key = load_openssh_key(filename);
        int ret;

        if (!key)
                return 0;
        ret = key->encrypted;
        m_burn(key->keyblob, key->keyblob_size);
        m_free(key->keyblob);
        m_free(key);
        return ret;
}

static sign_key *openssh_read(const char *filename, char * UNUSED(passphrase))
{
        struct openssh_key *key;
        unsigned char *p;
        int ret, id, len, flags;
        int i, num_integers = 0;
        sign_key *retval = NULL;
        char *errmsg;
        unsigned char *modptr = NULL;
        int modlen = -9999;
        enum signkey_type type;

        sign_key *retkey;
        buffer * blobbuf = NULL;

        retkey = new_sign_key();

        key = load_openssh_key(filename);

        if (!key)
                return NULL;

        if (key->encrypted) {
                errmsg = "encrypted keys not supported currently";
                goto error;
#if 0
                /* matt TODO */
                /*
                 * Derive encryption key from passphrase and iv/salt:
                 * 
                 *  - let block A equal MD5(passphrase || iv)
                 *  - let block B equal MD5(A || passphrase || iv)
                 *  - block C would be MD5(B || passphrase || iv) and so on
                 *  - encryption key is the first N bytes of A || B
                 */
                struct MD5Context md5c;
                unsigned char keybuf[32];

                MD5Init(&md5c);
                MD5Update(&md5c, (unsigned char *)passphrase, strlen(passphrase));
                MD5Update(&md5c, (unsigned char *)key->iv, 8);
                MD5Final(keybuf, &md5c);

                MD5Init(&md5c);
                MD5Update(&md5c, keybuf, 16);
                MD5Update(&md5c, (unsigned char *)passphrase, strlen(passphrase));
                MD5Update(&md5c, (unsigned char *)key->iv, 8);
                MD5Final(keybuf+16, &md5c);

                /*
                 * Now decrypt the key blob.
                 */
                des3_decrypt_pubkey_ossh(keybuf, (unsigned char *)key->iv,
                                                                 key->keyblob, key->keyblob_len);

                memset(&md5c, 0, sizeof(md5c));
                memset(keybuf, 0, sizeof(keybuf));
#endif 
        }

        /*
         * Now we have a decrypted key blob, which contains an ASN.1
         * encoded private key. We must now untangle the ASN.1.
         *
         * We expect the whole key blob to be formatted as a SEQUENCE
         * (0x30 followed by a length code indicating that the rest of
         * the blob is part of the sequence). Within that SEQUENCE we
         * expect to see a bunch of INTEGERs. What those integers mean
         * depends on the key type:
         *
         *  - For RSA, we expect the integers to be 0, n, e, d, p, q,
         *      dmp1, dmq1, iqmp in that order. (The last three are d mod
         *      (p-1), d mod (q-1), inverse of q mod p respectively.)
         *
         *  - For DSA, we expect them to be 0, p, q, g, y, x in that
         *      order.
         */
        
        p = key->keyblob;

        /* Expect the SEQUENCE header. Take its absence as a failure to decrypt. */
        ret = ber_read_id_len(p, key->keyblob_len, &id, &len, &flags);
        p += ret;
        if (ret < 0 || id != 16) {
                errmsg = "ASN.1 decoding failure - wrong password?";
                goto error;
        }

        /* Expect a load of INTEGERs. */
        if (key->type == OSSH_RSA)
                num_integers = 9;
        else if (key->type == OSSH_DSA)
                num_integers = 6;
        else if (key->type == OSSH_EC)
                num_integers = 1;

        /*
         * Space to create key blob in.
         */
        blobbuf = buf_new(3000);

#ifdef DROPBEAR_DSS
        if (key->type == OSSH_DSA) {
                buf_putstring(blobbuf, "ssh-dss", 7);
                retkey->type = DROPBEAR_SIGNKEY_DSS;
        } 
#endif
#ifdef DROPBEAR_RSA
        if (key->type == OSSH_RSA) {
                buf_putstring(blobbuf, "ssh-rsa", 7);
                retkey->type = DROPBEAR_SIGNKEY_RSA;
        }
#endif

        for (i = 0; i < num_integers; i++) {
                ret = ber_read_id_len(p, key->keyblob+key->keyblob_len-p,
                                                          &id, &len, &flags);
                p += ret;
                if (ret < 0 || id != 2 ||
                        key->keyblob+key->keyblob_len-p < len) {
                        errmsg = "ASN.1 decoding failure";
                        goto error;
                }

                if (i == 0) {
                        /* First integer is a version indicator */
                        int expected = -1;
                        switch (key->type) {
                                case OSSH_RSA:
                                case OSSH_DSA:
                                        expected = 0;
                                        break;
                                case OSSH_EC:
                                        expected = 1;
                                        break;
                        }
                        if (len != 1 || p[0] != expected) {
                                errmsg = "Version number mismatch";
                                goto error;
                        }
                } else if (key->type == OSSH_RSA) {
                        /*
                         * OpenSSH key order is n, e, d, p, q, dmp1, dmq1, iqmp
                         * but we want e, n, d, p, q
                         */
                        if (i == 1) {
                                /* Save the details for after we deal with number 2. */
                                modptr = p;
                                modlen = len;
                        } else if (i >= 2 && i <= 5) {
                                buf_putstring(blobbuf, (const char*)p, len);
                                if (i == 2) {
                                        buf_putstring(blobbuf, (const char*)modptr, modlen);
                                }
                        }
                } else if (key->type == OSSH_DSA) {
                        /*
                         * OpenSSH key order is p, q, g, y, x,
                         * we want the same.
                         */
                        buf_putstring(blobbuf, (const char*)p, len);
                }

                /* Skip past the number. */
                p += len;
        }

#ifdef DROPBEAR_ECDSA
        if (key->type == OSSH_EC) {
                unsigned char* private_key_bytes = NULL;
                int private_key_len = 0;
                unsigned char* public_key_bytes = NULL;
                int public_key_len = 0;
                ecc_key *ecc = NULL;
                const struct dropbear_ecc_curve *curve = NULL;

                /* See SEC1 v2, Appendix C.4 */
                /* OpenSSL (so OpenSSH) seems to include the optional parts. */

                /* privateKey OCTET STRING, */
                ret = ber_read_id_len(p, key->keyblob+key->keyblob_len-p,
                                                          &id, &len, &flags);
                p += ret;
                /* id==4 for octet string */
                if (ret < 0 || id != 4 ||
                        key->keyblob+key->keyblob_len-p < len) {
                        errmsg = "ASN.1 decoding failure";
                        goto error;
                }
                private_key_bytes = p;
                private_key_len = len;
                p += len;

                /* parameters [0] ECDomainParameters {{ SECGCurveNames }} OPTIONAL, */
                ret = ber_read_id_len(p, key->keyblob+key->keyblob_len-p,
                                                          &id, &len, &flags);
                p += ret;
                /* id==0 */
                if (ret < 0 || id != 0) {
                        errmsg = "ASN.1 decoding failure";
                        goto error;
                }

                ret = ber_read_id_len(p, key->keyblob+key->keyblob_len-p,
                                                          &id, &len, &flags);
                p += ret;
                /* id==6 for object */
                if (ret < 0 || id != 6 ||
                        key->keyblob+key->keyblob_len-p < len) {
                        errmsg = "ASN.1 decoding failure";
                        goto error;
                }

                if (0) {}
#ifdef DROPBEAR_ECC_256
                else if (len == sizeof(OID_SEC256R1_BLOB) 
                        && memcmp(p, OID_SEC256R1_BLOB, len) == 0) {
                        retkey->type = DROPBEAR_SIGNKEY_ECDSA_NISTP256;
                        curve = &ecc_curve_nistp256;
                } 
#endif
#ifdef DROPBEAR_ECC_384
                else if (len == sizeof(OID_SEC384R1_BLOB)
                        && memcmp(p, OID_SEC384R1_BLOB, len) == 0) {
                        retkey->type = DROPBEAR_SIGNKEY_ECDSA_NISTP384;
                        curve = &ecc_curve_nistp384;
                } 
#endif
#ifdef DROPBEAR_ECC_521
                else if (len == sizeof(OID_SEC521R1_BLOB)
                        && memcmp(p, OID_SEC521R1_BLOB, len) == 0) {
                        retkey->type = DROPBEAR_SIGNKEY_ECDSA_NISTP521;
                        curve = &ecc_curve_nistp521;
                } 
#endif
                else {
                        errmsg = "Unknown ECC key type";
                        goto error;
                }
                p += len;

                /* publicKey [1] BIT STRING OPTIONAL */
                ret = ber_read_id_len(p, key->keyblob+key->keyblob_len-p,
                                                          &id, &len, &flags);
                p += ret;
                /* id==1 */
                if (ret < 0 || id != 1) {
                        errmsg = "ASN.1 decoding failure";
                        goto error;
                }

                ret = ber_read_id_len(p, key->keyblob+key->keyblob_len-p,
                                                          &id, &len, &flags);
                p += ret;
                /* id==3 for bit string */
                if (ret < 0 || id != 3 ||
                        key->keyblob+key->keyblob_len-p < len) {
                        errmsg = "ASN.1 decoding failure";
                        goto error;
                }
                public_key_bytes = p+1;
                public_key_len = len-1;
                p += len;

                buf_putbytes(blobbuf, public_key_bytes, public_key_len);
                ecc = buf_get_ecc_raw_pubkey(blobbuf, curve);
                if (!ecc) {
                        errmsg = "Error parsing ECC key";
                        goto error;
                }
                m_mp_alloc_init_multi((mp_int**)&ecc->k, NULL);
                if (mp_read_unsigned_bin(ecc->k, private_key_bytes, private_key_len)
                        != MP_OKAY) {
                        errmsg = "Error parsing ECC key";
                        goto error;
                }

                *signkey_key_ptr(retkey, retkey->type) = ecc;
        }
#endif /* DROPBEAR_ECDSA */

        /*
         * Now put together the actual key. Simplest way to do this is
         * to assemble our own key blobs and feed them to the createkey
         * functions; this is a bit faffy but it does mean we get all
         * the sanity checks for free.
         */
        if (key->type == OSSH_RSA || key->type == OSSH_DSA) {
                buf_setpos(blobbuf, 0);
                type = DROPBEAR_SIGNKEY_ANY;
                if (buf_get_priv_key(blobbuf, retkey, &type)
                                != DROPBEAR_SUCCESS) {
                        errmsg = "unable to create key structure";
                        sign_key_free(retkey);
                        retkey = NULL;
                        goto error;
                }
        }

        errmsg = NULL;                                   /* no error */
        retval = retkey;

        error:
        if (blobbuf) {
                buf_burn(blobbuf);
                buf_free(blobbuf);
        }
        m_burn(key->keyblob, key->keyblob_size);
        m_free(key->keyblob);
        m_burn(key, sizeof(*key));
        m_free(key);
        if (errmsg) {
                fprintf(stderr, "Error: %s\n", errmsg);
        }
        return retval;
}

static int openssh_write(const char *filename, sign_key *key,
                                  char *passphrase)
{
        buffer * keyblob = NULL;
        buffer * extrablob = NULL; /* used for calculated values to write */
        unsigned char *outblob = NULL;
        int outlen = -9999;
        struct mpint_pos numbers[9];
        int nnumbers = -1, pos = 0, len = 0, seqlen, i;
        char *header = NULL, *footer = NULL;
        char zero[1];
        int ret = 0;
        FILE *fp;

#ifdef DROPBEAR_RSA
        mp_int dmp1, dmq1, iqmp, tmpval; /* for rsa */
#endif

        if (
#ifdef DROPBEAR_RSA
                        key->type == DROPBEAR_SIGNKEY_RSA ||
#endif
#ifdef DROPBEAR_DSS
                        key->type == DROPBEAR_SIGNKEY_DSS ||
#endif
                        0)
        {
                /*
                 * Fetch the key blobs.
                 */
                keyblob = buf_new(3000);
                buf_put_priv_key(keyblob, key, key->type);

                buf_setpos(keyblob, 0);
                /* skip the "ssh-rsa" or "ssh-dss" header */
                buf_incrpos(keyblob, buf_getint(keyblob));

                /*
                 * Find the sequence of integers to be encoded into the OpenSSH
                 * key blob, and also decide on the header line.
                 */
                numbers[0].start = zero; numbers[0].bytes = 1; zero[0] = '\0';

        #ifdef DROPBEAR_RSA
                if (key->type == DROPBEAR_SIGNKEY_RSA) {

                        if (key->rsakey->p == NULL || key->rsakey->q == NULL) {
                                fprintf(stderr, "Pre-0.33 Dropbear keys cannot be converted to OpenSSH keys.\n");
                                goto error;
                        }

                        /* e */
                        numbers[2].bytes = buf_getint(keyblob);
                        numbers[2].start = buf_getptr(keyblob, numbers[2].bytes);
                        buf_incrpos(keyblob, numbers[2].bytes);
                        
                        /* n */
                        numbers[1].bytes = buf_getint(keyblob);
                        numbers[1].start = buf_getptr(keyblob, numbers[1].bytes);
                        buf_incrpos(keyblob, numbers[1].bytes);
                        
                        /* d */
                        numbers[3].bytes = buf_getint(keyblob);
                        numbers[3].start = buf_getptr(keyblob, numbers[3].bytes);
                        buf_incrpos(keyblob, numbers[3].bytes);
                        
                        /* p */
                        numbers[4].bytes = buf_getint(keyblob);
                        numbers[4].start = buf_getptr(keyblob, numbers[4].bytes);
                        buf_incrpos(keyblob, numbers[4].bytes);
                        
                        /* q */
                        numbers[5].bytes = buf_getint(keyblob);
                        numbers[5].start = buf_getptr(keyblob, numbers[5].bytes);
                        buf_incrpos(keyblob, numbers[5].bytes);

                        /* now calculate some extra parameters: */
                        m_mp_init(&tmpval);
                        m_mp_init(&dmp1);
                        m_mp_init(&dmq1);
                        m_mp_init(&iqmp);

                        /* dmp1 = d mod (p-1) */
                        if (mp_sub_d(key->rsakey->p, 1, &tmpval) != MP_OKAY) {
                                fprintf(stderr, "Bignum error for p-1\n");
                                goto error;
                        }
                        if (mp_mod(key->rsakey->d, &tmpval, &dmp1) != MP_OKAY) {
                                fprintf(stderr, "Bignum error for dmp1\n");
                                goto error;
                        }

                        /* dmq1 = d mod (q-1) */
                        if (mp_sub_d(key->rsakey->q, 1, &tmpval) != MP_OKAY) {
                                fprintf(stderr, "Bignum error for q-1\n");
                                goto error;
                        }
                        if (mp_mod(key->rsakey->d, &tmpval, &dmq1) != MP_OKAY) {
                                fprintf(stderr, "Bignum error for dmq1\n");
                                goto error;
                        }

                        /* iqmp = (q^-1) mod p */
                        if (mp_invmod(key->rsakey->q, key->rsakey->p, &iqmp) != MP_OKAY) {
                                fprintf(stderr, "Bignum error for iqmp\n");
                                goto error;
                        }

                        extrablob = buf_new(2000);
                        buf_putmpint(extrablob, &dmp1);
                        buf_putmpint(extrablob, &dmq1);
                        buf_putmpint(extrablob, &iqmp);
                        buf_setpos(extrablob, 0);
                        mp_clear(&dmp1);
                        mp_clear(&dmq1);
                        mp_clear(&iqmp);
                        mp_clear(&tmpval);
                        
                        /* dmp1 */
                        numbers[6].bytes = buf_getint(extrablob);
                        numbers[6].start = buf_getptr(extrablob, numbers[6].bytes);
                        buf_incrpos(extrablob, numbers[6].bytes);
                        
                        /* dmq1 */
                        numbers[7].bytes = buf_getint(extrablob);
                        numbers[7].start = buf_getptr(extrablob, numbers[7].bytes);
                        buf_incrpos(extrablob, numbers[7].bytes);
                        
                        /* iqmp */
                        numbers[8].bytes = buf_getint(extrablob);
                        numbers[8].start = buf_getptr(extrablob, numbers[8].bytes);
                        buf_incrpos(extrablob, numbers[8].bytes);

                        nnumbers = 9;
                        header = "-----BEGIN RSA PRIVATE KEY-----\n";
                        footer = "-----END RSA PRIVATE KEY-----\n";
                }
        #endif /* DROPBEAR_RSA */

        #ifdef DROPBEAR_DSS
                if (key->type == DROPBEAR_SIGNKEY_DSS) {

                        /* p */
                        numbers[1].bytes = buf_getint(keyblob);
                        numbers[1].start = buf_getptr(keyblob, numbers[1].bytes);
                        buf_incrpos(keyblob, numbers[1].bytes);

                        /* q */
                        numbers[2].bytes = buf_getint(keyblob);
                        numbers[2].start = buf_getptr(keyblob, numbers[2].bytes);
                        buf_incrpos(keyblob, numbers[2].bytes);

                        /* g */
                        numbers[3].bytes = buf_getint(keyblob);
                        numbers[3].start = buf_getptr(keyblob, numbers[3].bytes);
                        buf_incrpos(keyblob, numbers[3].bytes);

                        /* y */
                        numbers[4].bytes = buf_getint(keyblob);
                        numbers[4].start = buf_getptr(keyblob, numbers[4].bytes);
                        buf_incrpos(keyblob, numbers[4].bytes);

                        /* x */
                        numbers[5].bytes = buf_getint(keyblob);
                        numbers[5].start = buf_getptr(keyblob, numbers[5].bytes);
                        buf_incrpos(keyblob, numbers[5].bytes);

                        nnumbers = 6;
                        header = "-----BEGIN DSA PRIVATE KEY-----\n";
                        footer = "-----END DSA PRIVATE KEY-----\n";
                }
        #endif /* DROPBEAR_DSS */

                /*
                 * Now count up the total size of the ASN.1 encoded integers,
                 * so as to determine the length of the containing SEQUENCE.
                 */
                len = 0;
                for (i = 0; i < nnumbers; i++) {
                        len += ber_write_id_len(NULL, 2, numbers[i].bytes, 0);
                        len += numbers[i].bytes;
                }
                seqlen = len;
                /* Now add on the SEQUENCE header. */
                len += ber_write_id_len(NULL, 16, seqlen, ASN1_CONSTRUCTED);
                /* Round up to the cipher block size, ensuring we have at least one
                 * byte of padding (see below). */
                outlen = len;
                if (passphrase)
                        outlen = (outlen+8) &~ 7;

                /*
                 * Now we know how big outblob needs to be. Allocate it.
                 */
                outblob = (unsigned char*)m_malloc(outlen);

                /*
                 * And write the data into it.
                 */
                pos = 0;
                pos += ber_write_id_len(outblob+pos, 16, seqlen, ASN1_CONSTRUCTED);
                for (i = 0; i < nnumbers; i++) {
                        pos += ber_write_id_len(outblob+pos, 2, numbers[i].bytes, 0);
                        memcpy(outblob+pos, numbers[i].start, numbers[i].bytes);
                        pos += numbers[i].bytes;
                }
        } /* end RSA and DSS handling */

#ifdef DROPBEAR_ECDSA
        if (key->type == DROPBEAR_SIGNKEY_ECDSA_NISTP256
                || key->type == DROPBEAR_SIGNKEY_ECDSA_NISTP384
                || key->type == DROPBEAR_SIGNKEY_ECDSA_NISTP521) {

                /*  SEC1 V2 appendix c.4
                ECPrivateKey ::= SEQUENCE {
                        version INTEGER { ecPrivkeyVer1(1) } (ecPrivkeyVer1),
                        privateKey OCTET STRING,
                        parameters [0] ECDomainParameters {{ SECGCurveNames }} OPTIONAL, 
                        publicKey [1] BIT STRING OPTIONAL
                }
                */
                buffer *seq_buf = buf_new(400);
                ecc_key **eck = (ecc_key**)signkey_key_ptr(key, key->type);
                const long curve_size = (*eck)->dp->size;
                int curve_oid_len = 0;
                const void* curve_oid = NULL;
                unsigned long pubkey_size = 2*curve_size+1;
                int k_size;
                int err = 0;

                /* version. less than 10 bytes */
                buf_incrwritepos(seq_buf,
                        ber_write_id_len(buf_getwriteptr(seq_buf, 10), 2, 1, 0));
                buf_putbyte(seq_buf, 1);

                /* privateKey */
                k_size = mp_unsigned_bin_size((*eck)->k);
                dropbear_assert(k_size <= curve_size);
                buf_incrwritepos(seq_buf,
                        ber_write_id_len(buf_getwriteptr(seq_buf, 10), 4, k_size, 0));
            mp_to_unsigned_bin((*eck)->k, buf_getwriteptr(seq_buf, k_size));
                buf_incrwritepos(seq_buf, k_size);

                /* SECGCurveNames */
                switch (key->type)
                {
                        case DROPBEAR_SIGNKEY_ECDSA_NISTP256:
                                curve_oid_len = sizeof(OID_SEC256R1_BLOB);
                                curve_oid = OID_SEC256R1_BLOB;
                                break;
                        case DROPBEAR_SIGNKEY_ECDSA_NISTP384:
                                curve_oid_len = sizeof(OID_SEC384R1_BLOB);
                                curve_oid = OID_SEC384R1_BLOB;
                                break;
                        case DROPBEAR_SIGNKEY_ECDSA_NISTP521:
                                curve_oid_len = sizeof(OID_SEC521R1_BLOB);
                                curve_oid = OID_SEC521R1_BLOB;
                                break;
                        default:
                                dropbear_exit("Internal error");
                }

                buf_incrwritepos(seq_buf,
                        ber_write_id_len(buf_getwriteptr(seq_buf, 10), 0, 2+curve_oid_len, 0xa0));
                /* object == 6 */
                buf_incrwritepos(seq_buf,
                        ber_write_id_len(buf_getwriteptr(seq_buf, 10), 6, curve_oid_len, 0));
                buf_putbytes(seq_buf, curve_oid, curve_oid_len);

                buf_incrwritepos(seq_buf,
                        ber_write_id_len(buf_getwriteptr(seq_buf, 10), 1, 2+1+pubkey_size, 0xa0));
                buf_incrwritepos(seq_buf,
                        ber_write_id_len(buf_getwriteptr(seq_buf, 10), 3, 1+pubkey_size, 0));
                buf_putbyte(seq_buf, 0);
                err = ecc_ansi_x963_export(*eck, buf_getwriteptr(seq_buf, pubkey_size), &pubkey_size);
                if (err != CRYPT_OK) {
                        dropbear_exit("ECC error");
                }
                buf_incrwritepos(seq_buf, pubkey_size);

                buf_setpos(seq_buf, 0);
                        
                outblob = (unsigned char*)m_malloc(1000);

                pos = 0;
                pos += ber_write_id_len(outblob+pos, 16, seq_buf->len, ASN1_CONSTRUCTED);
                memcpy(&outblob[pos], seq_buf->data, seq_buf->len);
                pos += seq_buf->len;
                len = pos;
                outlen = len;

                buf_burn(seq_buf);
                buf_free(seq_buf);
                seq_buf = NULL;

                header = "-----BEGIN EC PRIVATE KEY-----\n";
                footer = "-----END EC PRIVATE KEY-----\n";
        }
#endif

        /*
         * Padding on OpenSSH keys is deterministic. The number of
         * padding bytes is always more than zero, and always at most
         * the cipher block length. The value of each padding byte is
         * equal to the number of padding bytes. So a plaintext that's
         * an exact multiple of the block size will be padded with 08
         * 08 08 08 08 08 08 08 (assuming a 64-bit block cipher); a
         * plaintext one byte less than a multiple of the block size
         * will be padded with just 01.
         * 
         * This enables the OpenSSL key decryption function to strip
         * off the padding algorithmically and return the unpadded
         * plaintext to the next layer: it looks at the final byte, and
         * then expects to find that many bytes at the end of the data
         * with the same value. Those are all removed and the rest is
         * returned.
         */
        dropbear_assert(pos == len);
        while (pos < outlen) {
                outblob[pos++] = outlen - len;
        }

        /*
         * Encrypt the key.
         */
        if (passphrase) {
                fprintf(stderr, "Encrypted keys aren't supported currently\n");
                goto error;
        }

        /*
         * And save it. We'll use Unix line endings just in case it's
         * subsequently transferred in binary mode.
         */
        if (strlen(filename) == 1 && filename[0] == '-') {
                fp = stdout;
        } else {
                fp = fopen(filename, "wb");       /* ensure Unix line endings */
        }
        if (!fp) {
                fprintf(stderr, "Failed opening output file\n");
                goto error;
        }
        fputs(header, fp);
        base64_encode_fp(fp, outblob, outlen, 64);
        fputs(footer, fp);
        fclose(fp);
        ret = 1;

        error:
        if (outblob) {
                memset(outblob, 0, outlen);
                m_free(outblob);
        }
        if (keyblob) {
                buf_burn(keyblob);
                buf_free(keyblob);
        }
        if (extrablob) {
                buf_burn(extrablob);
                buf_free(extrablob);
        }
        return ret;
}

#if 0
/* XXX TODO ssh.com stuff isn't going yet */

/* ----------------------------------------------------------------------
 * Code to read ssh.com private keys.
 */

/*
 * The format of the base64 blob is largely ssh2-packet-formatted,
 * except that mpints are a bit different: they're more like the
 * old ssh1 mpint. You have a 32-bit bit count N, followed by
 * (N+7)/8 bytes of data.
 * 
 * So. The blob contains:
 * 
 *  - uint32 0x3f6ff9eb    (magic number)
 *  - uint32 size                        (total blob size)
 *  - string key-type            (see below)
 *  - string cipher-type          (tells you if key is encrypted)
 *  - string encrypted-blob
 * 
 * (The first size field includes the size field itself and the
 * magic number before it. All other size fields are ordinary ssh2
 * strings, so the size field indicates how much data is to
 * _follow_.)
 * 
 * The encrypted blob, once decrypted, contains a single string
 * which in turn contains the payload. (This allows padding to be
 * added after that string while still making it clear where the
 * real payload ends. Also it probably makes for a reasonable
 * decryption check.)
 * 
 * The payload blob, for an RSA key, contains:
 *  - mpint e
 *  - mpint d
 *  - mpint n  (yes, the public and private stuff is intermixed)
 *  - mpint u  (presumably inverse of p mod q)
 *  - mpint p  (p is the smaller prime)
 *  - mpint q  (q is the larger)
 * 
 * For a DSA key, the payload blob contains:
 *  - uint32 0
 *  - mpint p
 *  - mpint g
 *  - mpint q
 *  - mpint y
 *  - mpint x
 * 
 * Alternatively, if the parameters are `predefined', that
 * (0,p,g,q) sequence can be replaced by a uint32 1 and a string
 * containing some predefined parameter specification. *shudder*,
 * but I doubt we'll encounter this in real life.
 * 
 * The key type strings are ghastly. The RSA key I looked at had a
 * type string of
 * 
 *   `if-modn{sign{rsa-pkcs1-sha1},encrypt{rsa-pkcs1v2-oaep}}'
 * 
 * and the DSA key wasn't much better:
 * 
 *   `dl-modp{sign{dsa-nist-sha1},dh{plain}}'
 * 
 * It isn't clear that these will always be the same. I think it
 * might be wise just to look at the `if-modn{sign{rsa' and
 * `dl-modp{sign{dsa' prefixes.
 * 
 * Finally, the encryption. The cipher-type string appears to be
 * either `none' or `3des-cbc'. Looks as if this is SSH2-style
 * 3des-cbc (i.e. outer cbc rather than inner). The key is created
 * from the passphrase by means of yet another hashing faff:
 * 
 *  - first 16 bytes are MD5(passphrase)
 *  - next 16 bytes are MD5(passphrase || first 16 bytes)
 *  - if there were more, they'd be MD5(passphrase || first 32),
 *      and so on.
 */

#define SSHCOM_MAGIC_NUMBER 0x3f6ff9eb

struct sshcom_key {
        char comment[256];                               /* allowing any length is overkill */
        unsigned char *keyblob;
        int keyblob_len, keyblob_size;
};

static struct sshcom_key *load_sshcom_key(const char *filename)
{
        struct sshcom_key *ret;
        FILE *fp;
        char buffer[256];
        int len;
        char *errmsg, *p;
        int headers_done;
        char base64_bit[4];
        int base64_chars = 0;

        ret = snew(struct sshcom_key);
        ret->comment[0] = '\0';
        ret->keyblob = NULL;
        ret->keyblob_len = ret->keyblob_size = 0;

        fp = fopen(filename, "r");
        if (!fp) {
                errmsg = "Unable to open key file";
                goto error;
        }
        if (!fgets(buffer, sizeof(buffer), fp) ||
                0 != strcmp(buffer, "---- BEGIN SSH2 ENCRYPTED PRIVATE KEY ----\n")) {
                errmsg = "File does not begin with ssh.com key header";
                goto error;
        }

        headers_done = 0;
        while (1) {
                if (!fgets(buffer, sizeof(buffer), fp)) {
                        errmsg = "Unexpected end of file";
                        goto error;
                }
                if (!strcmp(buffer, "---- END SSH2 ENCRYPTED PRIVATE KEY ----\n"))
                        break;                                   /* done */
                if ((p = strchr(buffer, ':')) != NULL) {
                        if (headers_done) {
                                errmsg = "Header found in body of key data";
                                goto error;
                        }
                        *p++ = '\0';
                        while (*p && isspace((unsigned char)*p)) p++;
                        /*
                         * Header lines can end in a trailing backslash for
                         * continuation.
                         */
                        while ((len = strlen(p)) > (int)(sizeof(buffer) - (p-buffer) -1) ||
                                   p[len-1] != '\n' || p[len-2] == '\\') {
                                if (len > (int)((p-buffer) + sizeof(buffer)-2)) {
                                        errmsg = "Header line too long to deal with";
                                        goto error;
                                }
                                if (!fgets(p+len-2, sizeof(buffer)-(p-buffer)-(len-2), fp)) {
                                        errmsg = "Unexpected end of file";
                                        goto error;
                                }
                        }
                        p[strcspn(p, "\n")] = '\0';
                        if (!strcmp(buffer, "Comment")) {
                                /* Strip quotes in comment if present. */
                                if (p[0] == '"' && p[strlen(p)-1] == '"') {
                                        p++;
                                        p[strlen(p)-1] = '\0';
                                }
                                strncpy(ret->comment, p, sizeof(ret->comment));
                                ret->comment[sizeof(ret->comment)-1] = '\0';
                        }
                } else {
                        headers_done = 1;

                        p = buffer;
                        while (isbase64(*p)) {
                                base64_bit[base64_chars++] = *p;
                                if (base64_chars == 4) {
                                        unsigned char out[3];

                                        base64_chars = 0;

                                        len = base64_decode_atom(base64_bit, out);

                                        if (len <= 0) {
                                                errmsg = "Invalid base64 encoding";
                                                goto error;
                                        }

                                        if (ret->keyblob_len + len > ret->keyblob_size) {
                                                ret->keyblob_size = ret->keyblob_len + len + 256;
                                                ret->keyblob = sresize(ret->keyblob, ret->keyblob_size,
                                                                                           unsigned char);
                                        }

                                        memcpy(ret->keyblob + ret->keyblob_len, out, len);
                                        ret->keyblob_len += len;
                                }

                                p++;
                        }
                }
        }

        if (ret->keyblob_len == 0 || !ret->keyblob) {
                errmsg = "Key body not present";
                goto error;
        }

        return ret;

        error:
        if (ret) {
                if (ret->keyblob) {
                        memset(ret->keyblob, 0, ret->keyblob_size);
                        m_free(ret->keyblob);
                }
                memset(&ret, 0, sizeof(ret));
                m_free(ret);
        }
        return NULL;
}

int sshcom_encrypted(const char *filename, char **comment)
{
        struct sshcom_key *key = load_sshcom_key(filename);
        int pos, len, answer;

        *comment = NULL;
        if (!key)
                return 0;

        /*
         * Check magic number.
         */
        if (GET_32BIT(key->keyblob) != 0x3f6ff9eb)
                return 0;                                         /* key is invalid */

        /*
         * Find the cipher-type string.
         */
        answer = 0;
        pos = 8;
        if (key->keyblob_len < pos+4)
                goto done;                                       /* key is far too short */
        pos += 4 + GET_32BIT(key->keyblob + pos);   /* skip key type */
        if (key->keyblob_len < pos+4)
                goto done;                                       /* key is far too short */
        len = GET_32BIT(key->keyblob + pos);   /* find cipher-type length */
        if (key->keyblob_len < pos+4+len)
                goto done;                                       /* cipher type string is incomplete */
        if (len != 4 || 0 != memcmp(key->keyblob + pos + 4, "none", 4))
                answer = 1;

        done:
        *comment = dupstr(key->comment);
        memset(key->keyblob, 0, key->keyblob_size);
        m_free(key->keyblob);
        memset(&key, 0, sizeof(key));
        m_free(key);
        return answer;
}

static int sshcom_read_mpint(void *data, int len, struct mpint_pos *ret)
{
        int bits;
        int bytes;
        unsigned char *d = (unsigned char *) data;

        if (len < 4)
                goto error;
        bits = GET_32BIT(d);

        bytes = (bits + 7) / 8;
        if (len < 4+bytes)
                goto error;

        ret->start = d + 4;
        ret->bytes = bytes;
        return bytes+4;

        error:
        ret->start = NULL;
        ret->bytes = -1;
        return len;                                             /* ensure further calls fail as well */
}

static int sshcom_put_mpint(void *target, void *data, int len)
{
        unsigned char *d = (unsigned char *)target;
        unsigned char *i = (unsigned char *)data;
        int bits = len * 8 - 1;

        while (bits > 0) {
                if (*i & (1 << (bits & 7)))
                        break;
                if (!(bits-- & 7))
                        i++, len--;
        }

        PUT_32BIT(d, bits+1);
        memcpy(d+4, i, len);
        return len+4;
}

sign_key *sshcom_read(const char *filename, char *passphrase)
{
        struct sshcom_key *key = load_sshcom_key(filename);
        char *errmsg;
        int pos, len;
        const char prefix_rsa[] = "if-modn{sign{rsa";
        const char prefix_dsa[] = "dl-modp{sign{dsa";
        enum { RSA, DSA } type;
        int encrypted;
        char *ciphertext;
        int cipherlen;
        struct ssh2_userkey *ret = NULL, *retkey;
        const struct ssh_signkey *alg;
        unsigned char *blob = NULL;
        int blobsize, publen, privlen;

        if (!key)
                return NULL;

        /*
         * Check magic number.
         */
        if (GET_32BIT(key->keyblob) != SSHCOM_MAGIC_NUMBER) {
                errmsg = "Key does not begin with magic number";
                goto error;
        }

        /*
         * Determine the key type.
         */
        pos = 8;
        if (key->keyblob_len < pos+4 ||
                (len = GET_32BIT(key->keyblob + pos)) > key->keyblob_len - pos - 4) {
                errmsg = "Key blob does not contain a key type string";
                goto error;
        }
        if (len > sizeof(prefix_rsa) - 1 &&
                !memcmp(key->keyblob+pos+4, prefix_rsa, sizeof(prefix_rsa) - 1)) {
                type = RSA;
        } else if (len > sizeof(prefix_dsa) - 1 &&
                !memcmp(key->keyblob+pos+4, prefix_dsa, sizeof(prefix_dsa) - 1)) {
                type = DSA;
        } else {
                errmsg = "Key is of unknown type";
                goto error;
        }
        pos += 4+len;

        /*
         * Determine the cipher type.
         */
        if (key->keyblob_len < pos+4 ||
                (len = GET_32BIT(key->keyblob + pos)) > key->keyblob_len - pos - 4) {
                errmsg = "Key blob does not contain a cipher type string";
                goto error;
        }
        if (len == 4 && !memcmp(key->keyblob+pos+4, "none", 4))
                encrypted = 0;
        else if (len == 8 && !memcmp(key->keyblob+pos+4, "3des-cbc", 8))
                encrypted = 1;
        else {
                errmsg = "Key encryption is of unknown type";
                goto error;
        }
        pos += 4+len;

        /*
         * Get hold of the encrypted part of the key.
         */
        if (key->keyblob_len < pos+4 ||
                (len = GET_32BIT(key->keyblob + pos)) > key->keyblob_len - pos - 4) {
                errmsg = "Key blob does not contain actual key data";
                goto error;
        }
        ciphertext = (char *)key->keyblob + pos + 4;
        cipherlen = len;
        if (cipherlen == 0) {
                errmsg = "Length of key data is zero";
                goto error;
        }

        /*
         * Decrypt it if necessary.
         */
        if (encrypted) {
                /*
                 * Derive encryption key from passphrase and iv/salt:
                 * 
                 *  - let block A equal MD5(passphrase)
                 *  - let block B equal MD5(passphrase || A)
                 *  - block C would be MD5(passphrase || A || B) and so on
                 *  - encryption key is the first N bytes of A || B
                 */
                struct MD5Context md5c;
                unsigned char keybuf[32], iv[8];

                if (cipherlen % 8 != 0) {
                        errmsg = "Encrypted part of key is not a multiple of cipher block"
                                " size";
                        goto error;
                }

                MD5Init(&md5c);
                MD5Update(&md5c, (unsigned char *)passphrase, strlen(passphrase));
                MD5Final(keybuf, &md5c);

                MD5Init(&md5c);
                MD5Update(&md5c, (unsigned char *)passphrase, strlen(passphrase));
                MD5Update(&md5c, keybuf, 16);
                MD5Final(keybuf+16, &md5c);

                /*
                 * Now decrypt the key blob.
                 */
                memset(iv, 0, sizeof(iv));
                des3_decrypt_pubkey_ossh(keybuf, iv, (unsigned char *)ciphertext,
                                                                 cipherlen);

                memset(&md5c, 0, sizeof(md5c));
                memset(keybuf, 0, sizeof(keybuf));

                /*
                 * Hereafter we return WRONG_PASSPHRASE for any parsing
                 * error. (But only if we've just tried to decrypt it!
                 * Returning WRONG_PASSPHRASE for an unencrypted key is
                 * automatic doom.)
                 */
                if (encrypted)
                        ret = SSH2_WRONG_PASSPHRASE;
        }

        /*
         * Strip away the containing string to get to the real meat.
         */
        len = GET_32BIT(ciphertext);
        if (len > cipherlen-4) {
                errmsg = "containing string was ill-formed";
                goto error;
        }
        ciphertext += 4;
        cipherlen = len;

        /*
         * Now we break down into RSA versus DSA. In either case we'll
         * construct public and private blobs in our own format, and
         * end up feeding them to alg->createkey().
         */
        blobsize = cipherlen + 256;
        blob = snewn(blobsize, unsigned char);
        privlen = 0;
        if (type == RSA) {
                struct mpint_pos n, e, d, u, p, q;
                int pos = 0;
                pos += sshcom_read_mpint(ciphertext+pos, cipherlen-pos, &e);
                pos += sshcom_read_mpint(ciphertext+pos, cipherlen-pos, &d);
                pos += sshcom_read_mpint(ciphertext+pos, cipherlen-pos, &n);
                pos += sshcom_read_mpint(ciphertext+pos, cipherlen-pos, &u);
                pos += sshcom_read_mpint(ciphertext+pos, cipherlen-pos, &p);
                pos += sshcom_read_mpint(ciphertext+pos, cipherlen-pos, &q);
                if (!q.start) {
                        errmsg = "key data did not contain six integers";
                        goto error;
                }

                alg = &ssh_rsa;
                pos = 0;
                pos += put_string(blob+pos, "ssh-rsa", 7);
                pos += put_mp(blob+pos, e.start, e.bytes);
                pos += put_mp(blob+pos, n.start, n.bytes);
                publen = pos;
                pos += put_string(blob+pos, d.start, d.bytes);
                pos += put_mp(blob+pos, q.start, q.bytes);
                pos += put_mp(blob+pos, p.start, p.bytes);
                pos += put_mp(blob+pos, u.start, u.bytes);
                privlen = pos - publen;
        } else if (type == DSA) {
                struct mpint_pos p, q, g, x, y;
                int pos = 4;
                if (GET_32BIT(ciphertext) != 0) {
                        errmsg = "predefined DSA parameters not supported";
                        goto error;
                }
                pos += sshcom_read_mpint(ciphertext+pos, cipherlen-pos, &p);
                pos += sshcom_read_mpint(ciphertext+pos, cipherlen-pos, &g);
                pos += sshcom_read_mpint(ciphertext+pos, cipherlen-pos, &q);
                pos += sshcom_read_mpint(ciphertext+pos, cipherlen-pos, &y);
                pos += sshcom_read_mpint(ciphertext+pos, cipherlen-pos, &x);
                if (!x.start) {
                        errmsg = "key data did not contain five integers";
                        goto error;
                }

                alg = &ssh_dss;
                pos = 0;
                pos += put_string(blob+pos, "ssh-dss", 7);
                pos += put_mp(blob+pos, p.start, p.bytes);
                pos += put_mp(blob+pos, q.start, q.bytes);
                pos += put_mp(blob+pos, g.start, g.bytes);
                pos += put_mp(blob+pos, y.start, y.bytes);
                publen = pos;
                pos += put_mp(blob+pos, x.start, x.bytes);
                privlen = pos - publen;
        }

        dropbear_assert(privlen > 0);                      /* should have bombed by now if not */

        retkey = snew(struct ssh2_userkey);
        retkey->alg = alg;
        retkey->data = alg->createkey(blob, publen, blob+publen, privlen);
        if (!retkey->data) {
                m_free(retkey);
                errmsg = "unable to create key data structure";
                goto error;
        }
        retkey->comment = dupstr(key->comment);

        errmsg = NULL; /* no error */
        ret = retkey;

        error:
        if (blob) {
                memset(blob, 0, blobsize);
                m_free(blob);
        }
        memset(key->keyblob, 0, key->keyblob_size);
        m_free(key->keyblob);
        memset(&key, 0, sizeof(key));
        m_free(key);
        return ret;
}

int sshcom_write(const char *filename, sign_key *key,
                                 char *passphrase)
{
        unsigned char *pubblob, *privblob;
        int publen, privlen;
        unsigned char *outblob;
        int outlen;
        struct mpint_pos numbers[6];
        int nnumbers, initial_zero, pos, lenpos, i;
        char *type;
        char *ciphertext;
        int cipherlen;
        int ret = 0;
        FILE *fp;

        /*
         * Fetch the key blobs.
         */
        pubblob = key->alg->public_blob(key->data, &publen);
        privblob = key->alg->private_blob(key->data, &privlen);
        outblob = NULL;

        /*
         * Find the sequence of integers to be encoded into the OpenSSH
         * key blob, and also decide on the header line.
         */
        if (key->alg == &ssh_rsa) {
                int pos;
                struct mpint_pos n, e, d, p, q, iqmp;

                pos = 4 + GET_32BIT(pubblob);
                pos += ssh2_read_mpint(pubblob+pos, publen-pos, &e);
                pos += ssh2_read_mpint(pubblob+pos, publen-pos, &n);
                pos = 0;
                pos += ssh2_read_mpint(privblob+pos, privlen-pos, &d);
                pos += ssh2_read_mpint(privblob+pos, privlen-pos, &p);
                pos += ssh2_read_mpint(privblob+pos, privlen-pos, &q);
                pos += ssh2_read_mpint(privblob+pos, privlen-pos, &iqmp);

                dropbear_assert(e.start && iqmp.start); /* can't go wrong */

                numbers[0] = e;
                numbers[1] = d;
                numbers[2] = n;
                numbers[3] = iqmp;
                numbers[4] = q;
                numbers[5] = p;

                nnumbers = 6;
                initial_zero = 0;
                type = "if-modn{sign{rsa-pkcs1-sha1},encrypt{rsa-pkcs1v2-oaep}}";
        } else if (key->alg == &ssh_dss) {
                int pos;
                struct mpint_pos p, q, g, y, x;

                pos = 4 + GET_32BIT(pubblob);
                pos += ssh2_read_mpint(pubblob+pos, publen-pos, &p);
                pos += ssh2_read_mpint(pubblob+pos, publen-pos, &q);
                pos += ssh2_read_mpint(pubblob+pos, publen-pos, &g);
                pos += ssh2_read_mpint(pubblob+pos, publen-pos, &y);
                pos = 0;
                pos += ssh2_read_mpint(privblob+pos, privlen-pos, &x);

                dropbear_assert(y.start && x.start); /* can't go wrong */

                numbers[0] = p;
                numbers[1] = g;
                numbers[2] = q;
                numbers[3] = y;
                numbers[4] = x;

                nnumbers = 5;
                initial_zero = 1;
                type = "dl-modp{sign{dsa-nist-sha1},dh{plain}}";
        } else {
                dropbear_assert(0);                                      /* zoinks! */
        }

        /*
         * Total size of key blob will be somewhere under 512 plus
         * combined length of integers. We'll calculate the more
         * precise size as we construct the blob.
         */
        outlen = 512;
        for (i = 0; i < nnumbers; i++)
                outlen += 4 + numbers[i].bytes;
        outblob = snewn(outlen, unsigned char);

        /*
         * Create the unencrypted key blob.
         */
        pos = 0;
        PUT_32BIT(outblob+pos, SSHCOM_MAGIC_NUMBER); pos += 4;
        pos += 4;                                                          /* length field, fill in later */
        pos += put_string(outblob+pos, type, strlen(type));
        {
                char *ciphertype = passphrase ? "3des-cbc" : "none";
                pos += put_string(outblob+pos, ciphertype, strlen(ciphertype));
        }
        lenpos = pos;                                      /* remember this position */
        pos += 4;                                                          /* encrypted-blob size */
        pos += 4;                                                          /* encrypted-payload size */
        if (initial_zero) {
                PUT_32BIT(outblob+pos, 0);
                pos += 4;
        }
        for (i = 0; i < nnumbers; i++)
                pos += sshcom_put_mpint(outblob+pos,
                                                                numbers[i].start, numbers[i].bytes);
        /* Now wrap up the encrypted payload. */
        PUT_32BIT(outblob+lenpos+4, pos - (lenpos+8));
        /* Pad encrypted blob to a multiple of cipher block size. */
        if (passphrase) {
                int padding = -(pos - (lenpos+4)) & 7;
                while (padding--)
                        outblob[pos++] = random_byte();
        }
        ciphertext = (char *)outblob+lenpos+4;
        cipherlen = pos - (lenpos+4);
        dropbear_assert(!passphrase || cipherlen % 8 == 0);
        /* Wrap up the encrypted blob string. */
        PUT_32BIT(outblob+lenpos, cipherlen);
        /* And finally fill in the total length field. */
        PUT_32BIT(outblob+4, pos);

        dropbear_assert(pos < outlen);

        /*
         * Encrypt the key.
         */
        if (passphrase) {
                /*
                 * Derive encryption key from passphrase and iv/salt:
                 * 
                 *  - let block A equal MD5(passphrase)
                 *  - let block B equal MD5(passphrase || A)
                 *  - block C would be MD5(passphrase || A || B) and so on
                 *  - encryption key is the first N bytes of A || B
                 */
                struct MD5Context md5c;
                unsigned char keybuf[32], iv[8];

                MD5Init(&md5c);
                MD5Update(&md5c, (unsigned char *)passphrase, strlen(passphrase));
                MD5Final(keybuf, &md5c);

                MD5Init(&md5c);
                MD5Update(&md5c, (unsigned char *)passphrase, strlen(passphrase));
                MD5Update(&md5c, keybuf, 16);
                MD5Final(keybuf+16, &md5c);

                /*
                 * Now decrypt the key blob.
                 */
                memset(iv, 0, sizeof(iv));
                des3_encrypt_pubkey_ossh(keybuf, iv, (unsigned char *)ciphertext,
                                                                 cipherlen);

                memset(&md5c, 0, sizeof(md5c));
                memset(keybuf, 0, sizeof(keybuf));
        }

        /*
         * And save it. We'll use Unix line endings just in case it's
         * subsequently transferred in binary mode.
         */
        fp = fopen(filename, "wb");       /* ensure Unix line endings */
        if (!fp)
                goto error;
        fputs("---- BEGIN SSH2 ENCRYPTED PRIVATE KEY ----\n", fp);
        fprintf(fp, "Comment: \"");
        /*
         * Comment header is broken with backslash-newline if it goes
         * over 70 chars. Although it's surrounded by quotes, it
         * _doesn't_ escape backslashes or quotes within the string.
         * Don't ask me, I didn't design it.
         */
        {
                int slen = 60;                                     /* starts at 60 due to "Comment: " */
                char *c = key->comment;
                while ((int)strlen(c) > slen) {
                        fprintf(fp, "%.*s\\\n", slen, c);
                        c += slen;
                        slen = 70;                                         /* allow 70 chars on subsequent lines */
                }
                fprintf(fp, "%s\"\n", c);
        }
        base64_encode_fp(fp, outblob, pos, 70);
        fputs("---- END SSH2 ENCRYPTED PRIVATE KEY ----\n", fp);
        fclose(fp);
        ret = 1;

        error:
        if (outblob) {
                memset(outblob, 0, outlen);
                m_free(outblob);
        }
        if (privblob) {
                memset(privblob, 0, privlen);
                m_free(privblob);
        }
        if (pubblob) {
                memset(pubblob, 0, publen);
                m_free(pubblob);
        }
        return ret;
}
#endif /* ssh.com stuff disabled */