7cca0d81 |
1 | #include <stdio.h> |
2 | #include <stdlib.h> |
65a22376 |
3 | #include <assert.h> |
7cca0d81 |
4 | |
e5574168 |
5 | #include "ssh.h" |
5c72ca61 |
6 | #include "misc.h" |
e5574168 |
7 | |
5c72ca61 |
8 | static void sha_mpint(SHA_State * s, Bignum b) |
9 | { |
5c72ca61 |
10 | unsigned char lenbuf[4]; |
11 | int len; |
12 | len = (bignum_bitcount(b) + 8) / 8; |
13 | PUT_32BIT(lenbuf, len); |
14 | SHA_Bytes(s, lenbuf, 4); |
15 | while (len-- > 0) { |
16 | lenbuf[0] = bignum_byte(b, len); |
17 | SHA_Bytes(s, lenbuf, 1); |
18 | } |
19 | memset(lenbuf, 0, sizeof(lenbuf)); |
20 | } |
21 | |
22 | static void sha512_mpint(SHA512_State * s, Bignum b) |
23 | { |
5c72ca61 |
24 | unsigned char lenbuf[4]; |
25 | int len; |
26 | len = (bignum_bitcount(b) + 8) / 8; |
27 | PUT_32BIT(lenbuf, len); |
28 | SHA512_Bytes(s, lenbuf, 4); |
29 | while (len-- > 0) { |
30 | lenbuf[0] = bignum_byte(b, len); |
31 | SHA512_Bytes(s, lenbuf, 1); |
32 | } |
33 | memset(lenbuf, 0, sizeof(lenbuf)); |
34 | } |
9c621433 |
35 | |
32874aea |
36 | static void getstring(char **data, int *datalen, char **p, int *length) |
37 | { |
7cca0d81 |
38 | *p = NULL; |
39 | if (*datalen < 4) |
32874aea |
40 | return; |
7cca0d81 |
41 | *length = GET_32BIT(*data); |
32874aea |
42 | *datalen -= 4; |
43 | *data += 4; |
7cca0d81 |
44 | if (*datalen < *length) |
32874aea |
45 | return; |
7cca0d81 |
46 | *p = *data; |
32874aea |
47 | *data += *length; |
48 | *datalen -= *length; |
7cca0d81 |
49 | } |
32874aea |
50 | static Bignum getmp(char **data, int *datalen) |
51 | { |
7cca0d81 |
52 | char *p; |
3709bfe9 |
53 | int length; |
7cca0d81 |
54 | Bignum b; |
55 | |
56 | getstring(data, datalen, &p, &length); |
57 | if (!p) |
32874aea |
58 | return NULL; |
7cca0d81 |
59 | if (p[0] & 0x80) |
32874aea |
60 | return NULL; /* negative mp */ |
9202b1b2 |
61 | b = bignum_from_bytes((unsigned char *)p, length); |
7cca0d81 |
62 | return b; |
63 | } |
64 | |
32874aea |
65 | static Bignum get160(char **data, int *datalen) |
66 | { |
7cca0d81 |
67 | Bignum b; |
68 | |
9202b1b2 |
69 | b = bignum_from_bytes((unsigned char *)*data, 20); |
32874aea |
70 | *data += 20; |
71 | *datalen -= 20; |
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72 | |
7cca0d81 |
73 | return b; |
74 | } |
75 | |
32874aea |
76 | static void *dss_newkey(char *data, int len) |
77 | { |
7cca0d81 |
78 | char *p; |
79 | int slen; |
e055a386 |
80 | struct dss_key *dss; |
81 | |
3d88e64d |
82 | dss = snew(struct dss_key); |
32874aea |
83 | if (!dss) |
84 | return NULL; |
7cca0d81 |
85 | getstring(&data, &len, &p, &slen); |
9c621433 |
86 | |
87 | #ifdef DEBUG_DSS |
88 | { |
32874aea |
89 | int i; |
90 | printf("key:"); |
91 | for (i = 0; i < len; i++) |
92 | printf(" %02x", (unsigned char) (data[i])); |
93 | printf("\n"); |
9c621433 |
94 | } |
95 | #endif |
96 | |
7cca0d81 |
97 | if (!p || memcmp(p, "ssh-dss", 7)) { |
dcbde236 |
98 | sfree(dss); |
e055a386 |
99 | return NULL; |
7cca0d81 |
100 | } |
e055a386 |
101 | dss->p = getmp(&data, &len); |
102 | dss->q = getmp(&data, &len); |
103 | dss->g = getmp(&data, &len); |
104 | dss->y = getmp(&data, &len); |
105 | |
106 | return dss; |
7cca0d81 |
107 | } |
108 | |
32874aea |
109 | static void dss_freekey(void *key) |
110 | { |
111 | struct dss_key *dss = (struct dss_key *) key; |
e055a386 |
112 | freebn(dss->p); |
113 | freebn(dss->q); |
114 | freebn(dss->g); |
115 | freebn(dss->y); |
dcbde236 |
116 | sfree(dss); |
e055a386 |
117 | } |
118 | |
32874aea |
119 | static char *dss_fmtkey(void *key) |
120 | { |
121 | struct dss_key *dss = (struct dss_key *) key; |
7cca0d81 |
122 | char *p; |
d5859615 |
123 | int len, i, pos, nibbles; |
124 | static const char hex[] = "0123456789abcdef"; |
e055a386 |
125 | if (!dss->p) |
32874aea |
126 | return NULL; |
127 | len = 8 + 4 + 1; /* 4 x "0x", punctuation, \0 */ |
128 | len += 4 * (bignum_bitcount(dss->p) + 15) / 16; |
129 | len += 4 * (bignum_bitcount(dss->q) + 15) / 16; |
130 | len += 4 * (bignum_bitcount(dss->g) + 15) / 16; |
131 | len += 4 * (bignum_bitcount(dss->y) + 15) / 16; |
3d88e64d |
132 | p = snewn(len, char); |
32874aea |
133 | if (!p) |
134 | return NULL; |
d5859615 |
135 | |
136 | pos = 0; |
32874aea |
137 | pos += sprintf(p + pos, "0x"); |
138 | nibbles = (3 + bignum_bitcount(dss->p)) / 4; |
139 | if (nibbles < 1) |
140 | nibbles = 1; |
141 | for (i = nibbles; i--;) |
142 | p[pos++] = |
143 | hex[(bignum_byte(dss->p, i / 2) >> (4 * (i % 2))) & 0xF]; |
144 | pos += sprintf(p + pos, ",0x"); |
145 | nibbles = (3 + bignum_bitcount(dss->q)) / 4; |
146 | if (nibbles < 1) |
147 | nibbles = 1; |
148 | for (i = nibbles; i--;) |
149 | p[pos++] = |
150 | hex[(bignum_byte(dss->q, i / 2) >> (4 * (i % 2))) & 0xF]; |
151 | pos += sprintf(p + pos, ",0x"); |
152 | nibbles = (3 + bignum_bitcount(dss->g)) / 4; |
153 | if (nibbles < 1) |
154 | nibbles = 1; |
155 | for (i = nibbles; i--;) |
156 | p[pos++] = |
157 | hex[(bignum_byte(dss->g, i / 2) >> (4 * (i % 2))) & 0xF]; |
158 | pos += sprintf(p + pos, ",0x"); |
159 | nibbles = (3 + bignum_bitcount(dss->y)) / 4; |
160 | if (nibbles < 1) |
161 | nibbles = 1; |
162 | for (i = nibbles; i--;) |
163 | p[pos++] = |
164 | hex[(bignum_byte(dss->y, i / 2) >> (4 * (i % 2))) & 0xF]; |
d5859615 |
165 | p[pos] = '\0'; |
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166 | return p; |
167 | } |
168 | |
32874aea |
169 | static char *dss_fingerprint(void *key) |
170 | { |
171 | struct dss_key *dss = (struct dss_key *) key; |
d5859615 |
172 | struct MD5Context md5c; |
173 | unsigned char digest[16], lenbuf[4]; |
32874aea |
174 | char buffer[16 * 3 + 40]; |
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175 | char *ret; |
176 | int numlen, i; |
177 | |
178 | MD5Init(&md5c); |
9202b1b2 |
179 | MD5Update(&md5c, (unsigned char *)"\0\0\0\7ssh-dss", 11); |
d5859615 |
180 | |
181 | #define ADD_BIGNUM(bignum) \ |
ddecd643 |
182 | numlen = (bignum_bitcount(bignum)+8)/8; \ |
d5859615 |
183 | PUT_32BIT(lenbuf, numlen); MD5Update(&md5c, lenbuf, 4); \ |
184 | for (i = numlen; i-- ;) { \ |
185 | unsigned char c = bignum_byte(bignum, i); \ |
186 | MD5Update(&md5c, &c, 1); \ |
187 | } |
e055a386 |
188 | ADD_BIGNUM(dss->p); |
189 | ADD_BIGNUM(dss->q); |
190 | ADD_BIGNUM(dss->g); |
191 | ADD_BIGNUM(dss->y); |
d5859615 |
192 | #undef ADD_BIGNUM |
193 | |
194 | MD5Final(digest, &md5c); |
195 | |
ddecd643 |
196 | sprintf(buffer, "ssh-dss %d ", bignum_bitcount(dss->p)); |
d5859615 |
197 | for (i = 0; i < 16; i++) |
32874aea |
198 | sprintf(buffer + strlen(buffer), "%s%02x", i ? ":" : "", |
199 | digest[i]); |
3d88e64d |
200 | ret = snewn(strlen(buffer) + 1, char); |
d5859615 |
201 | if (ret) |
32874aea |
202 | strcpy(ret, buffer); |
d5859615 |
203 | return ret; |
204 | } |
205 | |
e055a386 |
206 | static int dss_verifysig(void *key, char *sig, int siglen, |
32874aea |
207 | char *data, int datalen) |
208 | { |
209 | struct dss_key *dss = (struct dss_key *) key; |
7cca0d81 |
210 | char *p; |
c5fbd713 |
211 | int slen; |
7cca0d81 |
212 | char hash[20]; |
59600f67 |
213 | Bignum r, s, w, gu1p, yu2p, gu1yu2p, u1, u2, sha, v; |
7cca0d81 |
214 | int ret; |
215 | |
e055a386 |
216 | if (!dss->p) |
32874aea |
217 | return 0; |
7cca0d81 |
218 | |
9c621433 |
219 | #ifdef DEBUG_DSS |
220 | { |
32874aea |
221 | int i; |
222 | printf("sig:"); |
223 | for (i = 0; i < siglen; i++) |
224 | printf(" %02x", (unsigned char) (sig[i])); |
225 | printf("\n"); |
9c621433 |
226 | } |
227 | #endif |
7f7837c8 |
228 | /* |
229 | * Commercial SSH (2.0.13) and OpenSSH disagree over the format |
230 | * of a DSA signature. OpenSSH is in line with the IETF drafts: |
231 | * it uses a string "ssh-dss", followed by a 40-byte string |
232 | * containing two 160-bit integers end-to-end. Commercial SSH |
233 | * can't be bothered with the header bit, and considers a DSA |
234 | * signature blob to be _just_ the 40-byte string containing |
235 | * the two 160-bit integers. We tell them apart by measuring |
236 | * the length: length 40 means the commercial-SSH bug, anything |
237 | * else is assumed to be IETF-compliant. |
238 | */ |
32874aea |
239 | if (siglen != 40) { /* bug not present; read admin fields */ |
240 | getstring(&sig, &siglen, &p, &slen); |
241 | if (!p || slen != 7 || memcmp(p, "ssh-dss", 7)) { |
242 | return 0; |
243 | } |
244 | sig += 4, siglen -= 4; /* skip yet another length field */ |
7cca0d81 |
245 | } |
7cca0d81 |
246 | r = get160(&sig, &siglen); |
247 | s = get160(&sig, &siglen); |
248 | if (!r || !s) |
32874aea |
249 | return 0; |
7cca0d81 |
250 | |
251 | /* |
252 | * Step 1. w <- s^-1 mod q. |
253 | */ |
e055a386 |
254 | w = modinv(s, dss->q); |
7cca0d81 |
255 | |
256 | /* |
257 | * Step 2. u1 <- SHA(message) * w mod q. |
258 | */ |
9202b1b2 |
259 | SHA_Simple(data, datalen, (unsigned char *)hash); |
32874aea |
260 | p = hash; |
261 | slen = 20; |
262 | sha = get160(&p, &slen); |
e055a386 |
263 | u1 = modmul(sha, w, dss->q); |
7cca0d81 |
264 | |
265 | /* |
266 | * Step 3. u2 <- r * w mod q. |
267 | */ |
e055a386 |
268 | u2 = modmul(r, w, dss->q); |
7cca0d81 |
269 | |
270 | /* |
271 | * Step 4. v <- (g^u1 * y^u2 mod p) mod q. |
272 | */ |
e055a386 |
273 | gu1p = modpow(dss->g, u1, dss->p); |
e055a386 |
274 | yu2p = modpow(dss->y, u2, dss->p); |
e055a386 |
275 | gu1yu2p = modmul(gu1p, yu2p, dss->p); |
e055a386 |
276 | v = modmul(gu1yu2p, One, dss->q); |
7cca0d81 |
277 | |
278 | /* |
279 | * Step 5. v should now be equal to r. |
280 | */ |
281 | |
c5fbd713 |
282 | ret = !bignum_cmp(v, r); |
7cca0d81 |
283 | |
284 | freebn(w); |
7cca0d81 |
285 | freebn(sha); |
59600f67 |
286 | freebn(gu1p); |
287 | freebn(yu2p); |
288 | freebn(gu1yu2p); |
7cca0d81 |
289 | freebn(v); |
290 | freebn(r); |
291 | freebn(s); |
292 | |
293 | return ret; |
294 | } |
295 | |
32874aea |
296 | static unsigned char *dss_public_blob(void *key, int *len) |
297 | { |
298 | struct dss_key *dss = (struct dss_key *) key; |
65a22376 |
299 | int plen, qlen, glen, ylen, bloblen; |
300 | int i; |
301 | unsigned char *blob, *p; |
302 | |
32874aea |
303 | plen = (bignum_bitcount(dss->p) + 8) / 8; |
304 | qlen = (bignum_bitcount(dss->q) + 8) / 8; |
305 | glen = (bignum_bitcount(dss->g) + 8) / 8; |
306 | ylen = (bignum_bitcount(dss->y) + 8) / 8; |
65a22376 |
307 | |
308 | /* |
309 | * string "ssh-dss", mpint p, mpint q, mpint g, mpint y. Total |
310 | * 27 + sum of lengths. (five length fields, 20+7=27). |
311 | */ |
32874aea |
312 | bloblen = 27 + plen + qlen + glen + ylen; |
3d88e64d |
313 | blob = snewn(bloblen, unsigned char); |
65a22376 |
314 | p = blob; |
32874aea |
315 | PUT_32BIT(p, 7); |
316 | p += 4; |
317 | memcpy(p, "ssh-dss", 7); |
318 | p += 7; |
319 | PUT_32BIT(p, plen); |
320 | p += 4; |
321 | for (i = plen; i--;) |
322 | *p++ = bignum_byte(dss->p, i); |
323 | PUT_32BIT(p, qlen); |
324 | p += 4; |
325 | for (i = qlen; i--;) |
326 | *p++ = bignum_byte(dss->q, i); |
327 | PUT_32BIT(p, glen); |
328 | p += 4; |
329 | for (i = glen; i--;) |
330 | *p++ = bignum_byte(dss->g, i); |
331 | PUT_32BIT(p, ylen); |
332 | p += 4; |
333 | for (i = ylen; i--;) |
334 | *p++ = bignum_byte(dss->y, i); |
65a22376 |
335 | assert(p == blob + bloblen); |
336 | *len = bloblen; |
337 | return blob; |
338 | } |
339 | |
32874aea |
340 | static unsigned char *dss_private_blob(void *key, int *len) |
341 | { |
5c72ca61 |
342 | struct dss_key *dss = (struct dss_key *) key; |
343 | int xlen, bloblen; |
344 | int i; |
345 | unsigned char *blob, *p; |
5c72ca61 |
346 | |
347 | xlen = (bignum_bitcount(dss->x) + 8) / 8; |
348 | |
349 | /* |
7bedb13c |
350 | * mpint x, string[20] the SHA of p||q||g. Total 4 + xlen. |
5c72ca61 |
351 | */ |
7bedb13c |
352 | bloblen = 4 + xlen; |
3d88e64d |
353 | blob = snewn(bloblen, unsigned char); |
5c72ca61 |
354 | p = blob; |
355 | PUT_32BIT(p, xlen); |
356 | p += 4; |
357 | for (i = xlen; i--;) |
358 | *p++ = bignum_byte(dss->x, i); |
5c72ca61 |
359 | assert(p == blob + bloblen); |
360 | *len = bloblen; |
361 | return blob; |
65a22376 |
362 | } |
363 | |
364 | static void *dss_createkey(unsigned char *pub_blob, int pub_len, |
32874aea |
365 | unsigned char *priv_blob, int priv_len) |
366 | { |
5c72ca61 |
367 | struct dss_key *dss; |
368 | char *pb = (char *) priv_blob; |
369 | char *hash; |
370 | int hashlen; |
371 | SHA_State s; |
372 | unsigned char digest[20]; |
373 | Bignum ytest; |
374 | |
375 | dss = dss_newkey((char *) pub_blob, pub_len); |
376 | dss->x = getmp(&pb, &priv_len); |
5c72ca61 |
377 | |
378 | /* |
7bedb13c |
379 | * Check the obsolete hash in the old DSS key format. |
5c72ca61 |
380 | */ |
7bedb13c |
381 | hashlen = -1; |
382 | getstring(&pb, &priv_len, &hash, &hashlen); |
383 | if (hashlen == 20) { |
384 | SHA_Init(&s); |
385 | sha_mpint(&s, dss->p); |
386 | sha_mpint(&s, dss->q); |
387 | sha_mpint(&s, dss->g); |
388 | SHA_Final(&s, digest); |
389 | if (0 != memcmp(hash, digest, 20)) { |
390 | dss_freekey(dss); |
391 | return NULL; |
392 | } |
5c72ca61 |
393 | } |
394 | |
395 | /* |
396 | * Now ensure g^x mod p really is y. |
397 | */ |
398 | ytest = modpow(dss->g, dss->x, dss->p); |
399 | if (0 != bignum_cmp(ytest, dss->y)) { |
400 | dss_freekey(dss); |
401 | return NULL; |
402 | } |
403 | freebn(ytest); |
404 | |
405 | return dss; |
65a22376 |
406 | } |
407 | |
32874aea |
408 | static void *dss_openssh_createkey(unsigned char **blob, int *len) |
409 | { |
5c72ca61 |
410 | char **b = (char **) blob; |
411 | struct dss_key *dss; |
412 | |
3d88e64d |
413 | dss = snew(struct dss_key); |
5c72ca61 |
414 | if (!dss) |
415 | return NULL; |
416 | |
417 | dss->p = getmp(b, len); |
418 | dss->q = getmp(b, len); |
419 | dss->g = getmp(b, len); |
420 | dss->y = getmp(b, len); |
421 | dss->x = getmp(b, len); |
422 | |
423 | if (!dss->p || !dss->q || !dss->g || !dss->y || !dss->x) { |
424 | sfree(dss->p); |
425 | sfree(dss->q); |
426 | sfree(dss->g); |
427 | sfree(dss->y); |
428 | sfree(dss->x); |
429 | sfree(dss); |
430 | return NULL; |
431 | } |
432 | |
433 | return dss; |
45cebe79 |
434 | } |
435 | |
32874aea |
436 | static int dss_openssh_fmtkey(void *key, unsigned char *blob, int len) |
437 | { |
5c72ca61 |
438 | struct dss_key *dss = (struct dss_key *) key; |
439 | int bloblen, i; |
440 | |
441 | bloblen = |
442 | ssh2_bignum_length(dss->p) + |
443 | ssh2_bignum_length(dss->q) + |
444 | ssh2_bignum_length(dss->g) + |
445 | ssh2_bignum_length(dss->y) + |
446 | ssh2_bignum_length(dss->x); |
447 | |
448 | if (bloblen > len) |
449 | return bloblen; |
450 | |
451 | bloblen = 0; |
452 | #define ENC(x) \ |
453 | PUT_32BIT(blob+bloblen, ssh2_bignum_length((x))-4); bloblen += 4; \ |
454 | for (i = ssh2_bignum_length((x))-4; i-- ;) blob[bloblen++]=bignum_byte((x),i); |
455 | ENC(dss->p); |
456 | ENC(dss->q); |
457 | ENC(dss->g); |
458 | ENC(dss->y); |
459 | ENC(dss->x); |
460 | |
461 | return bloblen; |
ddecd643 |
462 | } |
463 | |
47a6b94c |
464 | static int dss_pubkey_bits(void *blob, int len) |
465 | { |
466 | struct dss_key *dss; |
467 | int ret; |
468 | |
469 | dss = dss_newkey((char *) blob, len); |
470 | ret = bignum_bitcount(dss->p); |
471 | dss_freekey(dss); |
472 | |
473 | return ret; |
474 | } |
475 | |
900852ab |
476 | static unsigned char *dss_sign(void *key, char *data, int datalen, int *siglen) |
32874aea |
477 | { |
5c72ca61 |
478 | /* |
479 | * The basic DSS signing algorithm is: |
480 | * |
481 | * - invent a random k between 1 and q-1 (exclusive). |
482 | * - Compute r = (g^k mod p) mod q. |
483 | * - Compute s = k^-1 * (hash + x*r) mod q. |
484 | * |
485 | * This has the dangerous properties that: |
486 | * |
487 | * - if an attacker in possession of the public key _and_ the |
488 | * signature (for example, the host you just authenticated |
489 | * to) can guess your k, he can reverse the computation of s |
490 | * and work out x = r^-1 * (s*k - hash) mod q. That is, he |
491 | * can deduce the private half of your key, and masquerade |
492 | * as you for as long as the key is still valid. |
493 | * |
494 | * - since r is a function purely of k and the public key, if |
495 | * the attacker only has a _range of possibilities_ for k |
496 | * it's easy for him to work through them all and check each |
497 | * one against r; he'll never be unsure of whether he's got |
498 | * the right one. |
499 | * |
500 | * - if you ever sign two different hashes with the same k, it |
501 | * will be immediately obvious because the two signatures |
502 | * will have the same r, and moreover an attacker in |
503 | * possession of both signatures (and the public key of |
504 | * course) can compute k = (hash1-hash2) * (s1-s2)^-1 mod q, |
505 | * and from there deduce x as before. |
506 | * |
507 | * - the Bleichenbacher attack on DSA makes use of methods of |
508 | * generating k which are significantly non-uniformly |
509 | * distributed; in particular, generating a 160-bit random |
510 | * number and reducing it mod q is right out. |
511 | * |
512 | * For this reason we must be pretty careful about how we |
513 | * generate our k. Since this code runs on Windows, with no |
514 | * particularly good system entropy sources, we can't trust our |
515 | * RNG itself to produce properly unpredictable data. Hence, we |
516 | * use a totally different scheme instead. |
517 | * |
518 | * What we do is to take a SHA-512 (_big_) hash of the private |
519 | * key x, and then feed this into another SHA-512 hash that |
520 | * also includes the message hash being signed. That is: |
521 | * |
522 | * proto_k = SHA512 ( SHA512(x) || SHA160(message) ) |
523 | * |
524 | * This number is 512 bits long, so reducing it mod q won't be |
525 | * noticeably non-uniform. So |
526 | * |
527 | * k = proto_k mod q |
528 | * |
529 | * This has the interesting property that it's _deterministic_: |
530 | * signing the same hash twice with the same key yields the |
531 | * same signature. |
532 | * |
5ced2a02 |
533 | * Despite this determinism, it's still not predictable to an |
534 | * attacker, because in order to repeat the SHA-512 |
535 | * construction that created it, the attacker would have to |
536 | * know the private key value x - and by assumption he doesn't, |
537 | * because if he knew that he wouldn't be attacking k! |
538 | * |
539 | * (This trick doesn't, _per se_, protect against reuse of k. |
540 | * Reuse of k is left to chance; all it does is prevent |
541 | * _excessively high_ chances of reuse of k due to entropy |
542 | * problems.) |
5c72ca61 |
543 | * |
544 | * Thanks to Colin Plumb for the general idea of using x to |
545 | * ensure k is hard to guess, and to the Cambridge University |
546 | * Computer Security Group for helping to argue out all the |
547 | * fine details. |
548 | */ |
549 | struct dss_key *dss = (struct dss_key *) key; |
550 | SHA512_State ss; |
551 | unsigned char digest[20], digest512[64]; |
552 | Bignum proto_k, k, gkp, hash, kinv, hxr, r, s; |
553 | unsigned char *bytes; |
554 | int nbytes, i; |
555 | |
556 | SHA_Simple(data, datalen, digest); |
557 | |
558 | /* |
559 | * Hash some identifying text plus x. |
560 | */ |
561 | SHA512_Init(&ss); |
562 | SHA512_Bytes(&ss, "DSA deterministic k generator", 30); |
563 | sha512_mpint(&ss, dss->x); |
564 | SHA512_Final(&ss, digest512); |
565 | |
566 | /* |
567 | * Now hash that digest plus the message hash. |
568 | */ |
569 | SHA512_Init(&ss); |
570 | SHA512_Bytes(&ss, digest512, sizeof(digest512)); |
571 | SHA512_Bytes(&ss, digest, sizeof(digest)); |
572 | SHA512_Final(&ss, digest512); |
573 | |
574 | memset(&ss, 0, sizeof(ss)); |
575 | |
576 | /* |
577 | * Now convert the result into a bignum, and reduce it mod q. |
578 | */ |
579 | proto_k = bignum_from_bytes(digest512, 64); |
580 | k = bigmod(proto_k, dss->q); |
581 | freebn(proto_k); |
582 | |
583 | memset(digest512, 0, sizeof(digest512)); |
584 | |
585 | /* |
586 | * Now we have k, so just go ahead and compute the signature. |
587 | */ |
588 | gkp = modpow(dss->g, k, dss->p); /* g^k mod p */ |
589 | r = bigmod(gkp, dss->q); /* r = (g^k mod p) mod q */ |
590 | freebn(gkp); |
591 | |
592 | hash = bignum_from_bytes(digest, 20); |
593 | kinv = modinv(k, dss->q); /* k^-1 mod q */ |
594 | hxr = bigmuladd(dss->x, r, hash); /* hash + x*r */ |
595 | s = modmul(kinv, hxr, dss->q); /* s = k^-1 * (hash + x*r) mod q */ |
596 | freebn(hxr); |
597 | freebn(kinv); |
598 | freebn(hash); |
599 | |
600 | /* |
601 | * Signature blob is |
602 | * |
603 | * string "ssh-dss" |
604 | * string two 20-byte numbers r and s, end to end |
605 | * |
606 | * i.e. 4+7 + 4+40 bytes. |
607 | */ |
608 | nbytes = 4 + 7 + 4 + 40; |
3d88e64d |
609 | bytes = snewn(nbytes, unsigned char); |
5c72ca61 |
610 | PUT_32BIT(bytes, 7); |
611 | memcpy(bytes + 4, "ssh-dss", 7); |
612 | PUT_32BIT(bytes + 4 + 7, 40); |
613 | for (i = 0; i < 20; i++) { |
614 | bytes[4 + 7 + 4 + i] = bignum_byte(r, 19 - i); |
615 | bytes[4 + 7 + 4 + 20 + i] = bignum_byte(s, 19 - i); |
616 | } |
617 | freebn(r); |
618 | freebn(s); |
619 | |
620 | *siglen = nbytes; |
621 | return bytes; |
e055a386 |
622 | } |
623 | |
65a22376 |
624 | const struct ssh_signkey ssh_dss = { |
e055a386 |
625 | dss_newkey, |
626 | dss_freekey, |
7cca0d81 |
627 | dss_fmtkey, |
65a22376 |
628 | dss_public_blob, |
629 | dss_private_blob, |
630 | dss_createkey, |
45cebe79 |
631 | dss_openssh_createkey, |
ddecd643 |
632 | dss_openssh_fmtkey, |
47a6b94c |
633 | dss_pubkey_bits, |
d5859615 |
634 | dss_fingerprint, |
7cca0d81 |
635 | dss_verifysig, |
e055a386 |
636 | dss_sign, |
d5859615 |
637 | "ssh-dss", |
638 | "dss" |
e5574168 |
639 | }; |