X-Git-Url: https://git.distorted.org.uk/~mdw/sgt/putty/blobdiff_plain/e557416818242c2e8b14ec03d321740fd83619e4..33232c8fb2ed915484358cf5c758419a376fae8b:/sshdss.c diff --git a/sshdss.c b/sshdss.c index c651140e..01c452b9 100644 --- a/sshdss.c +++ b/sshdss.c @@ -1,5 +1,255 @@ +#include +#include + #include "ssh.h" +#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); } + +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 i, j, length; + Bignum b; + + getstring(data, datalen, &p, &length); + if (!p) + return NULL; + if (p[0] & 0x80) + return NULL; /* negative mp */ + b = newbn((length+1)/2); + for (i = 0; i < length; i++) { + j = length - 1 - i; + if (j & 1) + b[j/2+1] |= ((unsigned char)p[i]) << 8; + else + b[j/2+1] |= ((unsigned char)p[i]); + } + return b; +} + +static Bignum get160(char **data, int *datalen) { + char *p; + int i, j, length; + Bignum b; + + p = *data; + *data += 20; *datalen -= 20; + + length = 20; + while (length > 0 && !p[0]) + p++, length--; + b = newbn((length+1)/2); + for (i = 0; i < length; i++) { + j = length - 1 - i; + if (j & 1) + b[j/2+1] |= ((unsigned char)p[i]) << 8; + else + b[j/2+1] |= ((unsigned char)p[i]); + } + return b; +} + +static Bignum dss_p, dss_q, dss_g, dss_y; + +static void dss_setkey(char *data, int len) { + char *p; + int slen; + getstring(&data, &len, &p, &slen); + if (!p || memcmp(p, "ssh-dss", 7)) { + dss_p = NULL; + return; + } + dss_p = getmp(&data, &len); + dss_q = getmp(&data, &len); + dss_g = getmp(&data, &len); + dss_y = getmp(&data, &len); +} + +static char *dss_fmtkey(void) { + 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 * (dss_p[0] + dss_q[0] + dss_g[0] + dss_y[0]); /* digits */ + p = malloc(len); + if (!p) return NULL; + + pos = 0; + pos += sprintf(p+pos, "0x"); + nibbles = (3 + ssh1_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 + ssh1_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 + ssh1_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 + ssh1_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) { + 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 = (ssh1_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, "%d ", ssh1_bignum_bitcount(dss_p)); + for (i = 0; i < 16; i++) + sprintf(buffer+strlen(buffer), "%s%02x", i?":":"", digest[i]); + ret = malloc(strlen(buffer)+1); + if (ret) + strcpy(ret, buffer); + return ret; +} + +static int dss_verifysig(char *sig, int siglen, char *data, int datalen) { + char *p; + int i, slen; + char hash[20]; + Bignum qm2, r, s, w, i1, i2, i3, u1, u2, sha, v; + int ret; + + if (!dss_p) + return 0; + + /* + * 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 || memcmp(p, "ssh-dss", 7)) { + return 0; + } + sig += 4, siglen -= 4; /* skip yet another length field */ + } + r = get160(&sig, &siglen); + s = get160(&sig, &siglen); + if (!r || !s) + return 0; + + /* + * Step 1. w <- s^-1 mod q. + */ + w = newbn(dss_q[0]); + qm2 = copybn(dss_q); + decbn(qm2); decbn(qm2); + /* Now qm2 is q-2, and by Fermat's Little Theorem, s^qm2 == s^-1 (mod q). + * This is a silly way to do it; may fix it later. */ + modpow(s, qm2, dss_q, w); + + /* + * Step 2. u1 <- SHA(message) * w mod q. + */ + u1 = newbn(dss_q[0]); + SHA_Simple(data, datalen, hash); + p = hash; slen = 20; sha = get160(&p, &slen); + modmul(sha, w, dss_q, u1); + + /* + * Step 3. u2 <- r * w mod q. + */ + u2 = newbn(dss_q[0]); + modmul(r, w, dss_q, u2); + + /* + * Step 4. v <- (g^u1 * y^u2 mod p) mod q. + */ + i1 = newbn(dss_p[0]); + i2 = newbn(dss_p[0]); + i3 = newbn(dss_p[0]); + v = newbn(dss_q[0]); + modpow(dss_g, u1, dss_p, i1); + modpow(dss_y, u2, dss_p, i2); + modmul(i1, i2, dss_p, i3); + modmul(i3, One, dss_q, v); + + /* + * Step 5. v should now be equal to r. + */ + + ret = 1; + for (i = 1; i <= v[0] || i <= r[0]; i++) { + if ((i > v[0] && r[i] != 0) || + (i > r[0] && v[i] != 0) || + (i <= v[0] && i <= r[0] && r[i] != v[i])) + ret = 0; + } + + freebn(w); + freebn(qm2); + freebn(sha); + freebn(i1); + freebn(i2); + freebn(i3); + freebn(v); + freebn(r); + freebn(s); + + return ret; +} + struct ssh_hostkey ssh_dss = { - "ssh-dss" + dss_setkey, + dss_fmtkey, + dss_fingerprint, + dss_verifysig, + "ssh-dss", + "dss" };