X-Git-Url: https://git.distorted.org.uk/u/mdw/putty/blobdiff_plain/e557416818242c2e8b14ec03d321740fd83619e4..d92624dccee63e8bee8653e8ae845ffad3490b67:/sshdss.c diff --git a/sshdss.c b/sshdss.c index c651140e..71ad59e1 100644 --- a/sshdss.c +++ b/sshdss.c @@ -1,5 +1,388 @@ +#include +#include +#include + #include "ssh.h" -struct ssh_hostkey ssh_dss = { - "ssh-dss" +#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])) + +#define PUT_32BIT(cp, value) { \ + (cp)[0] = (unsigned char)((value) >> 24); \ + (cp)[1] = (unsigned char)((value) >> 16); \ + (cp)[2] = (unsigned char)((value) >> 8); \ + (cp)[3] = (unsigned char)(value); } + +#if 0 +#define DEBUG_DSS +#else +#define diagbn(x,y) +#endif + +static void getstring(char **data, int *datalen, char **p, int *length) +{ + *p = NULL; + if (*datalen < 4) + return; + *length = GET_32BIT(*data); + *datalen -= 4; + *data += 4; + if (*datalen < *length) + return; + *p = *data; + *data += *length; + *datalen -= *length; +} +static Bignum getmp(char **data, int *datalen) +{ + char *p; + int length; + Bignum b; + + getstring(data, datalen, &p, &length); + if (!p) + return NULL; + if (p[0] & 0x80) + return NULL; /* negative mp */ + b = bignum_from_bytes(p, length); + return b; +} + +static Bignum get160(char **data, int *datalen) +{ + Bignum b; + + b = bignum_from_bytes(*data, 20); + *data += 20; + *datalen -= 20; + + return b; +} + +struct dss_key { + Bignum p, q, g, y; +}; + +static void *dss_newkey(char *data, int len) +{ + char *p; + int slen; + struct dss_key *dss; + + dss = smalloc(sizeof(struct dss_key)); + if (!dss) + return NULL; + getstring(&data, &len, &p, &slen); + +#ifdef DEBUG_DSS + { + int i; + printf("key:"); + for (i = 0; i < len; i++) + printf(" %02x", (unsigned char) (data[i])); + printf("\n"); + } +#endif + + if (!p || memcmp(p, "ssh-dss", 7)) { + sfree(dss); + return NULL; + } + dss->p = getmp(&data, &len); + dss->q = getmp(&data, &len); + dss->g = getmp(&data, &len); + dss->y = getmp(&data, &len); + + return dss; +} + +static void dss_freekey(void *key) +{ + struct dss_key *dss = (struct dss_key *) key; + freebn(dss->p); + freebn(dss->q); + freebn(dss->g); + freebn(dss->y); + sfree(dss); +} + +static char *dss_fmtkey(void *key) +{ + struct dss_key *dss = (struct dss_key *) key; + char *p; + int len, i, pos, nibbles; + static const char hex[] = "0123456789abcdef"; + if (!dss->p) + return NULL; + len = 8 + 4 + 1; /* 4 x "0x", punctuation, \0 */ + len += 4 * (bignum_bitcount(dss->p) + 15) / 16; + len += 4 * (bignum_bitcount(dss->q) + 15) / 16; + len += 4 * (bignum_bitcount(dss->g) + 15) / 16; + len += 4 * (bignum_bitcount(dss->y) + 15) / 16; + p = smalloc(len); + if (!p) + return NULL; + + pos = 0; + pos += sprintf(p + pos, "0x"); + nibbles = (3 + bignum_bitcount(dss->p)) / 4; + if (nibbles < 1) + nibbles = 1; + for (i = nibbles; i--;) + p[pos++] = + hex[(bignum_byte(dss->p, i / 2) >> (4 * (i % 2))) & 0xF]; + pos += sprintf(p + pos, ",0x"); + nibbles = (3 + bignum_bitcount(dss->q)) / 4; + if (nibbles < 1) + nibbles = 1; + for (i = nibbles; i--;) + p[pos++] = + hex[(bignum_byte(dss->q, i / 2) >> (4 * (i % 2))) & 0xF]; + pos += sprintf(p + pos, ",0x"); + nibbles = (3 + bignum_bitcount(dss->g)) / 4; + if (nibbles < 1) + nibbles = 1; + for (i = nibbles; i--;) + p[pos++] = + hex[(bignum_byte(dss->g, i / 2) >> (4 * (i % 2))) & 0xF]; + pos += sprintf(p + pos, ",0x"); + nibbles = (3 + bignum_bitcount(dss->y)) / 4; + if (nibbles < 1) + nibbles = 1; + for (i = nibbles; i--;) + p[pos++] = + hex[(bignum_byte(dss->y, i / 2) >> (4 * (i % 2))) & 0xF]; + p[pos] = '\0'; + return p; +} + +static char *dss_fingerprint(void *key) +{ + struct dss_key *dss = (struct dss_key *) key; + struct MD5Context md5c; + unsigned char digest[16], lenbuf[4]; + char buffer[16 * 3 + 40]; + char *ret; + int numlen, i; + + MD5Init(&md5c); + MD5Update(&md5c, "\0\0\0\7ssh-dss", 11); + +#define ADD_BIGNUM(bignum) \ + numlen = (bignum_bitcount(bignum)+8)/8; \ + PUT_32BIT(lenbuf, numlen); MD5Update(&md5c, lenbuf, 4); \ + for (i = numlen; i-- ;) { \ + unsigned char c = bignum_byte(bignum, i); \ + MD5Update(&md5c, &c, 1); \ + } + ADD_BIGNUM(dss->p); + ADD_BIGNUM(dss->q); + ADD_BIGNUM(dss->g); + ADD_BIGNUM(dss->y); +#undef ADD_BIGNUM + + MD5Final(digest, &md5c); + + sprintf(buffer, "ssh-dss %d ", bignum_bitcount(dss->p)); + for (i = 0; i < 16; i++) + sprintf(buffer + strlen(buffer), "%s%02x", i ? ":" : "", + digest[i]); + ret = smalloc(strlen(buffer) + 1); + if (ret) + strcpy(ret, buffer); + return ret; +} + +static int dss_verifysig(void *key, char *sig, int siglen, + char *data, int datalen) +{ + struct dss_key *dss = (struct dss_key *) key; + char *p; + int slen; + char hash[20]; + Bignum r, s, w, gu1p, yu2p, gu1yu2p, u1, u2, sha, v; + int ret; + + if (!dss->p) + return 0; + +#ifdef DEBUG_DSS + { + int i; + printf("sig:"); + for (i = 0; i < siglen; i++) + printf(" %02x", (unsigned char) (sig[i])); + printf("\n"); + } +#endif + /* + * Commercial SSH (2.0.13) and OpenSSH disagree over the format + * of a DSA signature. OpenSSH is in line with the IETF drafts: + * it uses a string "ssh-dss", followed by a 40-byte string + * containing two 160-bit integers end-to-end. Commercial SSH + * can't be bothered with the header bit, and considers a DSA + * signature blob to be _just_ the 40-byte string containing + * the two 160-bit integers. We tell them apart by measuring + * the length: length 40 means the commercial-SSH bug, anything + * else is assumed to be IETF-compliant. + */ + if (siglen != 40) { /* bug not present; read admin fields */ + getstring(&sig, &siglen, &p, &slen); + if (!p || slen != 7 || memcmp(p, "ssh-dss", 7)) { + return 0; + } + sig += 4, siglen -= 4; /* skip yet another length field */ + } + diagbn("p=", dss->p); + diagbn("q=", dss->q); + diagbn("g=", dss->g); + diagbn("y=", dss->y); + r = get160(&sig, &siglen); + diagbn("r=", r); + s = get160(&sig, &siglen); + diagbn("s=", s); + if (!r || !s) + return 0; + + /* + * Step 1. w <- s^-1 mod q. + */ + w = modinv(s, dss->q); + diagbn("w=", w); + + /* + * Step 2. u1 <- SHA(message) * w mod q. + */ + SHA_Simple(data, datalen, hash); + p = hash; + slen = 20; + sha = get160(&p, &slen); + diagbn("sha=", sha); + u1 = modmul(sha, w, dss->q); + diagbn("u1=", u1); + + /* + * Step 3. u2 <- r * w mod q. + */ + u2 = modmul(r, w, dss->q); + diagbn("u2=", u2); + + /* + * Step 4. v <- (g^u1 * y^u2 mod p) mod q. + */ + gu1p = modpow(dss->g, u1, dss->p); + diagbn("gu1p=", gu1p); + yu2p = modpow(dss->y, u2, dss->p); + diagbn("yu2p=", yu2p); + gu1yu2p = modmul(gu1p, yu2p, dss->p); + diagbn("gu1yu2p=", gu1yu2p); + v = modmul(gu1yu2p, One, dss->q); + diagbn("gu1yu2q=v=", v); + diagbn("r=", r); + + /* + * Step 5. v should now be equal to r. + */ + + ret = !bignum_cmp(v, r); + + freebn(w); + freebn(sha); + freebn(gu1p); + freebn(yu2p); + freebn(gu1yu2p); + freebn(v); + freebn(r); + freebn(s); + + return ret; +} + +static unsigned char *dss_public_blob(void *key, int *len) +{ + struct dss_key *dss = (struct dss_key *) key; + int plen, qlen, glen, ylen, bloblen; + int i; + unsigned char *blob, *p; + + plen = (bignum_bitcount(dss->p) + 8) / 8; + qlen = (bignum_bitcount(dss->q) + 8) / 8; + glen = (bignum_bitcount(dss->g) + 8) / 8; + ylen = (bignum_bitcount(dss->y) + 8) / 8; + + /* + * string "ssh-dss", mpint p, mpint q, mpint g, mpint y. Total + * 27 + sum of lengths. (five length fields, 20+7=27). + */ + bloblen = 27 + plen + qlen + glen + ylen; + blob = smalloc(bloblen); + p = blob; + PUT_32BIT(p, 7); + p += 4; + memcpy(p, "ssh-dss", 7); + p += 7; + PUT_32BIT(p, plen); + p += 4; + for (i = plen; i--;) + *p++ = bignum_byte(dss->p, i); + PUT_32BIT(p, qlen); + p += 4; + for (i = qlen; i--;) + *p++ = bignum_byte(dss->q, i); + PUT_32BIT(p, glen); + p += 4; + for (i = glen; i--;) + *p++ = bignum_byte(dss->g, i); + PUT_32BIT(p, ylen); + p += 4; + for (i = ylen; i--;) + *p++ = bignum_byte(dss->y, i); + assert(p == blob + bloblen); + *len = bloblen; + return blob; +} + +static unsigned char *dss_private_blob(void *key, int *len) +{ + return NULL; /* can't handle DSS private keys */ +} + +static void *dss_createkey(unsigned char *pub_blob, int pub_len, + unsigned char *priv_blob, int priv_len) +{ + return NULL; /* can't handle DSS private keys */ +} + +static void *dss_openssh_createkey(unsigned char **blob, int *len) +{ + return NULL; /* can't handle DSS private keys */ +} + +static int dss_openssh_fmtkey(void *key, unsigned char *blob, int len) +{ + return -1; /* can't handle DSS private keys */ +} + +unsigned char *dss_sign(void *key, char *data, int datalen, int *siglen) +{ + return NULL; /* can't handle DSS private keys */ +} + +const struct ssh_signkey ssh_dss = { + dss_newkey, + dss_freekey, + dss_fmtkey, + dss_public_blob, + dss_private_blob, + dss_createkey, + dss_openssh_createkey, + dss_openssh_fmtkey, + dss_fingerprint, + dss_verifysig, + dss_sign, + "ssh-dss", + "dss" };