+++ /dev/null
-/*\r
- * Digital Signature Standard implementation for PuTTY.\r
- */\r
-\r
-#include <stdio.h>\r
-#include <stdlib.h>\r
-#include <assert.h>\r
-\r
-#include "ssh.h"\r
-#include "misc.h"\r
-\r
-static void sha_mpint(SHA_State * s, Bignum b)\r
-{\r
- unsigned char lenbuf[4];\r
- int len;\r
- len = (bignum_bitcount(b) + 8) / 8;\r
- PUT_32BIT(lenbuf, len);\r
- SHA_Bytes(s, lenbuf, 4);\r
- while (len-- > 0) {\r
- lenbuf[0] = bignum_byte(b, len);\r
- SHA_Bytes(s, lenbuf, 1);\r
- }\r
- memset(lenbuf, 0, sizeof(lenbuf));\r
-}\r
-\r
-static void sha512_mpint(SHA512_State * s, Bignum b)\r
-{\r
- unsigned char lenbuf[4];\r
- int len;\r
- len = (bignum_bitcount(b) + 8) / 8;\r
- PUT_32BIT(lenbuf, len);\r
- SHA512_Bytes(s, lenbuf, 4);\r
- while (len-- > 0) {\r
- lenbuf[0] = bignum_byte(b, len);\r
- SHA512_Bytes(s, lenbuf, 1);\r
- }\r
- memset(lenbuf, 0, sizeof(lenbuf));\r
-}\r
-\r
-static void getstring(char **data, int *datalen, char **p, int *length)\r
-{\r
- *p = NULL;\r
- if (*datalen < 4)\r
- return;\r
- *length = GET_32BIT(*data);\r
- *datalen -= 4;\r
- *data += 4;\r
- if (*datalen < *length)\r
- return;\r
- *p = *data;\r
- *data += *length;\r
- *datalen -= *length;\r
-}\r
-static Bignum getmp(char **data, int *datalen)\r
-{\r
- char *p;\r
- int length;\r
- Bignum b;\r
-\r
- getstring(data, datalen, &p, &length);\r
- if (!p)\r
- return NULL;\r
- if (p[0] & 0x80)\r
- return NULL; /* negative mp */\r
- b = bignum_from_bytes((unsigned char *)p, length);\r
- return b;\r
-}\r
-\r
-static Bignum get160(char **data, int *datalen)\r
-{\r
- Bignum b;\r
-\r
- b = bignum_from_bytes((unsigned char *)*data, 20);\r
- *data += 20;\r
- *datalen -= 20;\r
-\r
- return b;\r
-}\r
-\r
-static void *dss_newkey(char *data, int len)\r
-{\r
- char *p;\r
- int slen;\r
- struct dss_key *dss;\r
-\r
- dss = snew(struct dss_key);\r
- if (!dss)\r
- return NULL;\r
- getstring(&data, &len, &p, &slen);\r
-\r
-#ifdef DEBUG_DSS\r
- {\r
- int i;\r
- printf("key:");\r
- for (i = 0; i < len; i++)\r
- printf(" %02x", (unsigned char) (data[i]));\r
- printf("\n");\r
- }\r
-#endif\r
-\r
- if (!p || memcmp(p, "ssh-dss", 7)) {\r
- sfree(dss);\r
- return NULL;\r
- }\r
- dss->p = getmp(&data, &len);\r
- dss->q = getmp(&data, &len);\r
- dss->g = getmp(&data, &len);\r
- dss->y = getmp(&data, &len);\r
-\r
- return dss;\r
-}\r
-\r
-static void dss_freekey(void *key)\r
-{\r
- struct dss_key *dss = (struct dss_key *) key;\r
- freebn(dss->p);\r
- freebn(dss->q);\r
- freebn(dss->g);\r
- freebn(dss->y);\r
- sfree(dss);\r
-}\r
-\r
-static char *dss_fmtkey(void *key)\r
-{\r
- struct dss_key *dss = (struct dss_key *) key;\r
- char *p;\r
- int len, i, pos, nibbles;\r
- static const char hex[] = "0123456789abcdef";\r
- if (!dss->p)\r
- return NULL;\r
- len = 8 + 4 + 1; /* 4 x "0x", punctuation, \0 */\r
- len += 4 * (bignum_bitcount(dss->p) + 15) / 16;\r
- len += 4 * (bignum_bitcount(dss->q) + 15) / 16;\r
- len += 4 * (bignum_bitcount(dss->g) + 15) / 16;\r
- len += 4 * (bignum_bitcount(dss->y) + 15) / 16;\r
- p = snewn(len, char);\r
- if (!p)\r
- return NULL;\r
-\r
- pos = 0;\r
- pos += sprintf(p + pos, "0x");\r
- nibbles = (3 + bignum_bitcount(dss->p)) / 4;\r
- if (nibbles < 1)\r
- nibbles = 1;\r
- for (i = nibbles; i--;)\r
- p[pos++] =\r
- hex[(bignum_byte(dss->p, i / 2) >> (4 * (i % 2))) & 0xF];\r
- pos += sprintf(p + pos, ",0x");\r
- nibbles = (3 + bignum_bitcount(dss->q)) / 4;\r
- if (nibbles < 1)\r
- nibbles = 1;\r
- for (i = nibbles; i--;)\r
- p[pos++] =\r
- hex[(bignum_byte(dss->q, i / 2) >> (4 * (i % 2))) & 0xF];\r
- pos += sprintf(p + pos, ",0x");\r
- nibbles = (3 + bignum_bitcount(dss->g)) / 4;\r
- if (nibbles < 1)\r
- nibbles = 1;\r
- for (i = nibbles; i--;)\r
- p[pos++] =\r
- hex[(bignum_byte(dss->g, i / 2) >> (4 * (i % 2))) & 0xF];\r
- pos += sprintf(p + pos, ",0x");\r
- nibbles = (3 + bignum_bitcount(dss->y)) / 4;\r
- if (nibbles < 1)\r
- nibbles = 1;\r
- for (i = nibbles; i--;)\r
- p[pos++] =\r
- hex[(bignum_byte(dss->y, i / 2) >> (4 * (i % 2))) & 0xF];\r
- p[pos] = '\0';\r
- return p;\r
-}\r
-\r
-static char *dss_fingerprint(void *key)\r
-{\r
- struct dss_key *dss = (struct dss_key *) key;\r
- struct MD5Context md5c;\r
- unsigned char digest[16], lenbuf[4];\r
- char buffer[16 * 3 + 40];\r
- char *ret;\r
- int numlen, i;\r
-\r
- MD5Init(&md5c);\r
- MD5Update(&md5c, (unsigned char *)"\0\0\0\7ssh-dss", 11);\r
-\r
-#define ADD_BIGNUM(bignum) \\r
- numlen = (bignum_bitcount(bignum)+8)/8; \\r
- PUT_32BIT(lenbuf, numlen); MD5Update(&md5c, lenbuf, 4); \\r
- for (i = numlen; i-- ;) { \\r
- unsigned char c = bignum_byte(bignum, i); \\r
- MD5Update(&md5c, &c, 1); \\r
- }\r
- ADD_BIGNUM(dss->p);\r
- ADD_BIGNUM(dss->q);\r
- ADD_BIGNUM(dss->g);\r
- ADD_BIGNUM(dss->y);\r
-#undef ADD_BIGNUM\r
-\r
- MD5Final(digest, &md5c);\r
-\r
- sprintf(buffer, "ssh-dss %d ", bignum_bitcount(dss->p));\r
- for (i = 0; i < 16; i++)\r
- sprintf(buffer + strlen(buffer), "%s%02x", i ? ":" : "",\r
- digest[i]);\r
- ret = snewn(strlen(buffer) + 1, char);\r
- if (ret)\r
- strcpy(ret, buffer);\r
- return ret;\r
-}\r
-\r
-static int dss_verifysig(void *key, char *sig, int siglen,\r
- char *data, int datalen)\r
-{\r
- struct dss_key *dss = (struct dss_key *) key;\r
- char *p;\r
- int slen;\r
- char hash[20];\r
- Bignum r, s, w, gu1p, yu2p, gu1yu2p, u1, u2, sha, v;\r
- int ret;\r
-\r
- if (!dss->p)\r
- return 0;\r
-\r
-#ifdef DEBUG_DSS\r
- {\r
- int i;\r
- printf("sig:");\r
- for (i = 0; i < siglen; i++)\r
- printf(" %02x", (unsigned char) (sig[i]));\r
- printf("\n");\r
- }\r
-#endif\r
- /*\r
- * Commercial SSH (2.0.13) and OpenSSH disagree over the format\r
- * of a DSA signature. OpenSSH is in line with RFC 4253:\r
- * it uses a string "ssh-dss", followed by a 40-byte string\r
- * containing two 160-bit integers end-to-end. Commercial SSH\r
- * can't be bothered with the header bit, and considers a DSA\r
- * signature blob to be _just_ the 40-byte string containing\r
- * the two 160-bit integers. We tell them apart by measuring\r
- * the length: length 40 means the commercial-SSH bug, anything\r
- * else is assumed to be RFC-compliant.\r
- */\r
- if (siglen != 40) { /* bug not present; read admin fields */\r
- getstring(&sig, &siglen, &p, &slen);\r
- if (!p || slen != 7 || memcmp(p, "ssh-dss", 7)) {\r
- return 0;\r
- }\r
- sig += 4, siglen -= 4; /* skip yet another length field */\r
- }\r
- r = get160(&sig, &siglen);\r
- s = get160(&sig, &siglen);\r
- if (!r || !s)\r
- return 0;\r
-\r
- /*\r
- * Step 1. w <- s^-1 mod q.\r
- */\r
- w = modinv(s, dss->q);\r
-\r
- /*\r
- * Step 2. u1 <- SHA(message) * w mod q.\r
- */\r
- SHA_Simple(data, datalen, (unsigned char *)hash);\r
- p = hash;\r
- slen = 20;\r
- sha = get160(&p, &slen);\r
- u1 = modmul(sha, w, dss->q);\r
-\r
- /*\r
- * Step 3. u2 <- r * w mod q.\r
- */\r
- u2 = modmul(r, w, dss->q);\r
-\r
- /*\r
- * Step 4. v <- (g^u1 * y^u2 mod p) mod q.\r
- */\r
- gu1p = modpow(dss->g, u1, dss->p);\r
- yu2p = modpow(dss->y, u2, dss->p);\r
- gu1yu2p = modmul(gu1p, yu2p, dss->p);\r
- v = modmul(gu1yu2p, One, dss->q);\r
-\r
- /*\r
- * Step 5. v should now be equal to r.\r
- */\r
-\r
- ret = !bignum_cmp(v, r);\r
-\r
- freebn(w);\r
- freebn(sha);\r
- freebn(gu1p);\r
- freebn(yu2p);\r
- freebn(gu1yu2p);\r
- freebn(v);\r
- freebn(r);\r
- freebn(s);\r
-\r
- return ret;\r
-}\r
-\r
-static unsigned char *dss_public_blob(void *key, int *len)\r
-{\r
- struct dss_key *dss = (struct dss_key *) key;\r
- int plen, qlen, glen, ylen, bloblen;\r
- int i;\r
- unsigned char *blob, *p;\r
-\r
- plen = (bignum_bitcount(dss->p) + 8) / 8;\r
- qlen = (bignum_bitcount(dss->q) + 8) / 8;\r
- glen = (bignum_bitcount(dss->g) + 8) / 8;\r
- ylen = (bignum_bitcount(dss->y) + 8) / 8;\r
-\r
- /*\r
- * string "ssh-dss", mpint p, mpint q, mpint g, mpint y. Total\r
- * 27 + sum of lengths. (five length fields, 20+7=27).\r
- */\r
- bloblen = 27 + plen + qlen + glen + ylen;\r
- blob = snewn(bloblen, unsigned char);\r
- p = blob;\r
- PUT_32BIT(p, 7);\r
- p += 4;\r
- memcpy(p, "ssh-dss", 7);\r
- p += 7;\r
- PUT_32BIT(p, plen);\r
- p += 4;\r
- for (i = plen; i--;)\r
- *p++ = bignum_byte(dss->p, i);\r
- PUT_32BIT(p, qlen);\r
- p += 4;\r
- for (i = qlen; i--;)\r
- *p++ = bignum_byte(dss->q, i);\r
- PUT_32BIT(p, glen);\r
- p += 4;\r
- for (i = glen; i--;)\r
- *p++ = bignum_byte(dss->g, i);\r
- PUT_32BIT(p, ylen);\r
- p += 4;\r
- for (i = ylen; i--;)\r
- *p++ = bignum_byte(dss->y, i);\r
- assert(p == blob + bloblen);\r
- *len = bloblen;\r
- return blob;\r
-}\r
-\r
-static unsigned char *dss_private_blob(void *key, int *len)\r
-{\r
- struct dss_key *dss = (struct dss_key *) key;\r
- int xlen, bloblen;\r
- int i;\r
- unsigned char *blob, *p;\r
-\r
- xlen = (bignum_bitcount(dss->x) + 8) / 8;\r
-\r
- /*\r
- * mpint x, string[20] the SHA of p||q||g. Total 4 + xlen.\r
- */\r
- bloblen = 4 + xlen;\r
- blob = snewn(bloblen, unsigned char);\r
- p = blob;\r
- PUT_32BIT(p, xlen);\r
- p += 4;\r
- for (i = xlen; i--;)\r
- *p++ = bignum_byte(dss->x, i);\r
- assert(p == blob + bloblen);\r
- *len = bloblen;\r
- return blob;\r
-}\r
-\r
-static void *dss_createkey(unsigned char *pub_blob, int pub_len,\r
- unsigned char *priv_blob, int priv_len)\r
-{\r
- struct dss_key *dss;\r
- char *pb = (char *) priv_blob;\r
- char *hash;\r
- int hashlen;\r
- SHA_State s;\r
- unsigned char digest[20];\r
- Bignum ytest;\r
-\r
- dss = dss_newkey((char *) pub_blob, pub_len);\r
- dss->x = getmp(&pb, &priv_len);\r
-\r
- /*\r
- * Check the obsolete hash in the old DSS key format.\r
- */\r
- hashlen = -1;\r
- getstring(&pb, &priv_len, &hash, &hashlen);\r
- if (hashlen == 20) {\r
- SHA_Init(&s);\r
- sha_mpint(&s, dss->p);\r
- sha_mpint(&s, dss->q);\r
- sha_mpint(&s, dss->g);\r
- SHA_Final(&s, digest);\r
- if (0 != memcmp(hash, digest, 20)) {\r
- dss_freekey(dss);\r
- return NULL;\r
- }\r
- }\r
-\r
- /*\r
- * Now ensure g^x mod p really is y.\r
- */\r
- ytest = modpow(dss->g, dss->x, dss->p);\r
- if (0 != bignum_cmp(ytest, dss->y)) {\r
- dss_freekey(dss);\r
- return NULL;\r
- }\r
- freebn(ytest);\r
-\r
- return dss;\r
-}\r
-\r
-static void *dss_openssh_createkey(unsigned char **blob, int *len)\r
-{\r
- char **b = (char **) blob;\r
- struct dss_key *dss;\r
-\r
- dss = snew(struct dss_key);\r
- if (!dss)\r
- return NULL;\r
-\r
- dss->p = getmp(b, len);\r
- dss->q = getmp(b, len);\r
- dss->g = getmp(b, len);\r
- dss->y = getmp(b, len);\r
- dss->x = getmp(b, len);\r
-\r
- if (!dss->p || !dss->q || !dss->g || !dss->y || !dss->x) {\r
- sfree(dss->p);\r
- sfree(dss->q);\r
- sfree(dss->g);\r
- sfree(dss->y);\r
- sfree(dss->x);\r
- sfree(dss);\r
- return NULL;\r
- }\r
-\r
- return dss;\r
-}\r
-\r
-static int dss_openssh_fmtkey(void *key, unsigned char *blob, int len)\r
-{\r
- struct dss_key *dss = (struct dss_key *) key;\r
- int bloblen, i;\r
-\r
- bloblen =\r
- ssh2_bignum_length(dss->p) +\r
- ssh2_bignum_length(dss->q) +\r
- ssh2_bignum_length(dss->g) +\r
- ssh2_bignum_length(dss->y) +\r
- ssh2_bignum_length(dss->x);\r
-\r
- if (bloblen > len)\r
- return bloblen;\r
-\r
- bloblen = 0;\r
-#define ENC(x) \\r
- PUT_32BIT(blob+bloblen, ssh2_bignum_length((x))-4); bloblen += 4; \\r
- for (i = ssh2_bignum_length((x))-4; i-- ;) blob[bloblen++]=bignum_byte((x),i);\r
- ENC(dss->p);\r
- ENC(dss->q);\r
- ENC(dss->g);\r
- ENC(dss->y);\r
- ENC(dss->x);\r
-\r
- return bloblen;\r
-}\r
-\r
-static int dss_pubkey_bits(void *blob, int len)\r
-{\r
- struct dss_key *dss;\r
- int ret;\r
-\r
- dss = dss_newkey((char *) blob, len);\r
- ret = bignum_bitcount(dss->p);\r
- dss_freekey(dss);\r
-\r
- return ret;\r
-}\r
-\r
-static unsigned char *dss_sign(void *key, char *data, int datalen, int *siglen)\r
-{\r
- /*\r
- * The basic DSS signing algorithm is:\r
- * \r
- * - invent a random k between 1 and q-1 (exclusive).\r
- * - Compute r = (g^k mod p) mod q.\r
- * - Compute s = k^-1 * (hash + x*r) mod q.\r
- * \r
- * This has the dangerous properties that:\r
- * \r
- * - if an attacker in possession of the public key _and_ the\r
- * signature (for example, the host you just authenticated\r
- * to) can guess your k, he can reverse the computation of s\r
- * and work out x = r^-1 * (s*k - hash) mod q. That is, he\r
- * can deduce the private half of your key, and masquerade\r
- * as you for as long as the key is still valid.\r
- * \r
- * - since r is a function purely of k and the public key, if\r
- * the attacker only has a _range of possibilities_ for k\r
- * it's easy for him to work through them all and check each\r
- * one against r; he'll never be unsure of whether he's got\r
- * the right one.\r
- * \r
- * - if you ever sign two different hashes with the same k, it\r
- * will be immediately obvious because the two signatures\r
- * will have the same r, and moreover an attacker in\r
- * possession of both signatures (and the public key of\r
- * course) can compute k = (hash1-hash2) * (s1-s2)^-1 mod q,\r
- * and from there deduce x as before.\r
- * \r
- * - the Bleichenbacher attack on DSA makes use of methods of\r
- * generating k which are significantly non-uniformly\r
- * distributed; in particular, generating a 160-bit random\r
- * number and reducing it mod q is right out.\r
- * \r
- * For this reason we must be pretty careful about how we\r
- * generate our k. Since this code runs on Windows, with no\r
- * particularly good system entropy sources, we can't trust our\r
- * RNG itself to produce properly unpredictable data. Hence, we\r
- * use a totally different scheme instead.\r
- * \r
- * What we do is to take a SHA-512 (_big_) hash of the private\r
- * key x, and then feed this into another SHA-512 hash that\r
- * also includes the message hash being signed. That is:\r
- * \r
- * proto_k = SHA512 ( SHA512(x) || SHA160(message) )\r
- * \r
- * This number is 512 bits long, so reducing it mod q won't be\r
- * noticeably non-uniform. So\r
- * \r
- * k = proto_k mod q\r
- * \r
- * This has the interesting property that it's _deterministic_:\r
- * signing the same hash twice with the same key yields the\r
- * same signature.\r
- * \r
- * Despite this determinism, it's still not predictable to an\r
- * attacker, because in order to repeat the SHA-512\r
- * construction that created it, the attacker would have to\r
- * know the private key value x - and by assumption he doesn't,\r
- * because if he knew that he wouldn't be attacking k!\r
- *\r
- * (This trick doesn't, _per se_, protect against reuse of k.\r
- * Reuse of k is left to chance; all it does is prevent\r
- * _excessively high_ chances of reuse of k due to entropy\r
- * problems.)\r
- * \r
- * Thanks to Colin Plumb for the general idea of using x to\r
- * ensure k is hard to guess, and to the Cambridge University\r
- * Computer Security Group for helping to argue out all the\r
- * fine details.\r
- */\r
- struct dss_key *dss = (struct dss_key *) key;\r
- SHA512_State ss;\r
- unsigned char digest[20], digest512[64];\r
- Bignum proto_k, k, gkp, hash, kinv, hxr, r, s;\r
- unsigned char *bytes;\r
- int nbytes, i;\r
-\r
- SHA_Simple(data, datalen, digest);\r
-\r
- /*\r
- * Hash some identifying text plus x.\r
- */\r
- SHA512_Init(&ss);\r
- SHA512_Bytes(&ss, "DSA deterministic k generator", 30);\r
- sha512_mpint(&ss, dss->x);\r
- SHA512_Final(&ss, digest512);\r
-\r
- /*\r
- * Now hash that digest plus the message hash.\r
- */\r
- SHA512_Init(&ss);\r
- SHA512_Bytes(&ss, digest512, sizeof(digest512));\r
- SHA512_Bytes(&ss, digest, sizeof(digest));\r
- SHA512_Final(&ss, digest512);\r
-\r
- memset(&ss, 0, sizeof(ss));\r
-\r
- /*\r
- * Now convert the result into a bignum, and reduce it mod q.\r
- */\r
- proto_k = bignum_from_bytes(digest512, 64);\r
- k = bigmod(proto_k, dss->q);\r
- freebn(proto_k);\r
-\r
- memset(digest512, 0, sizeof(digest512));\r
-\r
- /*\r
- * Now we have k, so just go ahead and compute the signature.\r
- */\r
- gkp = modpow(dss->g, k, dss->p); /* g^k mod p */\r
- r = bigmod(gkp, dss->q); /* r = (g^k mod p) mod q */\r
- freebn(gkp);\r
-\r
- hash = bignum_from_bytes(digest, 20);\r
- kinv = modinv(k, dss->q); /* k^-1 mod q */\r
- hxr = bigmuladd(dss->x, r, hash); /* hash + x*r */\r
- s = modmul(kinv, hxr, dss->q); /* s = k^-1 * (hash + x*r) mod q */\r
- freebn(hxr);\r
- freebn(kinv);\r
- freebn(hash);\r
-\r
- /*\r
- * Signature blob is\r
- * \r
- * string "ssh-dss"\r
- * string two 20-byte numbers r and s, end to end\r
- * \r
- * i.e. 4+7 + 4+40 bytes.\r
- */\r
- nbytes = 4 + 7 + 4 + 40;\r
- bytes = snewn(nbytes, unsigned char);\r
- PUT_32BIT(bytes, 7);\r
- memcpy(bytes + 4, "ssh-dss", 7);\r
- PUT_32BIT(bytes + 4 + 7, 40);\r
- for (i = 0; i < 20; i++) {\r
- bytes[4 + 7 + 4 + i] = bignum_byte(r, 19 - i);\r
- bytes[4 + 7 + 4 + 20 + i] = bignum_byte(s, 19 - i);\r
- }\r
- freebn(r);\r
- freebn(s);\r
-\r
- *siglen = nbytes;\r
- return bytes;\r
-}\r
-\r
-const struct ssh_signkey ssh_dss = {\r
- dss_newkey,\r
- dss_freekey,\r
- dss_fmtkey,\r
- dss_public_blob,\r
- dss_private_blob,\r
- dss_createkey,\r
- dss_openssh_createkey,\r
- dss_openssh_fmtkey,\r
- dss_pubkey_bits,\r
- dss_fingerprint,\r
- dss_verifysig,\r
- dss_sign,\r
- "ssh-dss",\r
- "dss"\r
-};\r
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