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[secnet] / rsa.c
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3b83c932
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1/* This file is part of secnet, and is distributed under the terms of
2 the GNU General Public License version 2 or later.
3
4 Copyright (C) 1995-2002 Stephen Early
5 Copyright (C) 2001 Simon Tatham
6 Copyright (C) 2002 Ian Jackson
7 */
fe5e9cc4 8
2fe58dfd 9#include <stdio.h>
3b83c932 10#include <string.h>
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11#include <gmp.h>
12#include "secnet.h"
13#include "util.h"
14
15#define AUTHFILE_ID_STRING "SSH PRIVATE KEY FILE FORMAT 1.1\n"
16
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17#define mpp(s,n) do { char *p = mpz_get_str(NULL,16,n); printf("%s 0x%sL\n", s, p); free(p); } while (0)
18
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19struct rsapriv {
20 closure_t cl;
21 struct rsaprivkey_if ops;
22 struct cloc loc;
2fe58dfd 23 MP_INT n;
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24 MP_INT p, dp;
25 MP_INT q, dq;
26 MP_INT w;
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27};
28struct rsapub {
29 closure_t cl;
30 struct rsapubkey_if ops;
31 struct cloc loc;
32 MP_INT e;
33 MP_INT n;
34};
35/* Sign data. NB data must be smaller than modulus */
36
9941ae2e
MW
37#define RSA_MAX_MODBYTES 2048
38/* The largest modulus I've seen is 15360 bits, which works out at 1920
39 * bytes. Using keys this big is quite implausible, but it doesn't cost us
40 * much to support them.
41 */
42
fe5e9cc4 43static const char *hexchars="0123456789abcdef";
2fe58dfd 44
2cd2cf05
MW
45static void emsa_pkcs1(MP_INT *n, MP_INT *m,
46 const uint8_t *data, int32_t datalen)
2fe58dfd 47{
9941ae2e 48 char buff[2*RSA_MAX_MODBYTES + 1];
2fe58dfd 49 int msize, i;
2fe58dfd 50
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51 /* RSA PKCS#1 v1.5 signature padding:
52 *
53 * <------------ msize hex digits ---------->
54 *
55 * 00 01 ff ff .... ff ff 00 vv vv vv .... vv
56 *
57 * <--- datalen -->
58 * bytes
59 * = datalen*2 hex digits
60 *
61 * NB that according to PKCS#1 v1.5 we're supposed to include a
62 * hash function OID in the data. We don't do that (because we
63 * don't have the hash function OID to hand here), thus violating
64 * the spec in a way that affects interop but not security.
65 *
66 * -iwj 17.9.2002
67 */
68
2cd2cf05 69 msize=mpz_sizeinbase(n, 16);
2fe58dfd 70
3b83c932 71 if (datalen*2+6>=msize) {
4f5e39ec 72 fatal("rsa_sign: message too big");
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73 }
74
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75 strcpy(buff,"0001");
76
77 for (i=0; i<datalen; i++) {
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78 buff[msize+(-datalen+i)*2]=hexchars[(data[i]&0xf0)>>4];
79 buff[msize+(-datalen+i)*2+1]=hexchars[data[i]&0xf];
2fe58dfd 80 }
3454dce4 81
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82 buff[msize-datalen*2-2]= '0';
83 buff[msize-datalen*2-1]= '0';
84
85 for (i=4; i<msize-datalen*2-2; i++)
86 buff[i]='f';
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87
88 buff[msize]=0;
89
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90 mpz_set_str(m, buff, 16);
91}
92
93static string_t rsa_sign(void *sst, uint8_t *data, int32_t datalen)
94{
95 struct rsapriv *st=sst;
96 MP_INT a, b, u, v, tmp, tmp2;
97 string_t signature;
98
99 mpz_init(&a);
100 mpz_init(&b);
101
102 /* Construct the message representative. */
103 emsa_pkcs1(&st->n, &a, data, datalen);
2fe58dfd 104
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105 /*
106 * Produce an RSA signature (a^d mod n) using the Chinese
107 * Remainder Theorem. We compute:
108 *
109 * u = a^dp mod p (== a^d mod p, since dp == d mod (p-1))
110 * v = a^dq mod q (== a^d mod q, similarly)
111 *
112 * We also know w == iqmp * q, which has the property that w ==
113 * 0 mod q and w == 1 mod p. So (1-w) has the reverse property
114 * (congruent to 0 mod p and to 1 mod q). Hence we now compute
115 *
116 * b = w * u + (1-w) * v
117 * = w * (u-v) + v
118 *
119 * so that b is congruent to a^d both mod p and mod q. Hence b,
120 * reduced mod n, is the required signature.
121 */
122 mpz_init(&tmp);
123 mpz_init(&tmp2);
124 mpz_init(&u);
125 mpz_init(&v);
126
127 mpz_powm(&u, &a, &st->dp, &st->p);
128 mpz_powm(&v, &a, &st->dq, &st->q);
129 mpz_sub(&tmp, &u, &v);
130 mpz_mul(&tmp2, &tmp, &st->w);
131 mpz_add(&tmp, &tmp2, &v);
132 mpz_mod(&b, &tmp, &st->n);
133
134 mpz_clear(&tmp);
135 mpz_clear(&tmp2);
136 mpz_clear(&u);
137 mpz_clear(&v);
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138
139 signature=write_mpstring(&b);
140
141 mpz_clear(&b);
142 mpz_clear(&a);
143 return signature;
144}
145
fe5e9cc4 146static rsa_checksig_fn rsa_sig_check;
1caa23ff 147static bool_t rsa_sig_check(void *sst, uint8_t *data, int32_t datalen,
fe5e9cc4 148 cstring_t signature)
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149{
150 struct rsapub *st=sst;
151 MP_INT a, b, c;
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152 bool_t ok;
153
154 mpz_init(&a);
155 mpz_init(&b);
156 mpz_init(&c);
157
2cd2cf05 158 emsa_pkcs1(&st->n, &a, data, datalen);
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159
160 mpz_set_str(&b, signature, 16);
161
162 mpz_powm(&c, &b, &st->e, &st->n);
163
164 ok=(mpz_cmp(&a, &c)==0);
165
166 mpz_clear(&c);
167 mpz_clear(&b);
168 mpz_clear(&a);
169
170 return ok;
171}
172
173static list_t *rsapub_apply(closure_t *self, struct cloc loc, dict_t *context,
174 list_t *args)
175{
176 struct rsapub *st;
177 item_t *i;
178 string_t e,n;
179
b7886fd4 180 NEW(st);
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181 st->cl.description="rsapub";
182 st->cl.type=CL_RSAPUBKEY;
183 st->cl.apply=NULL;
184 st->cl.interface=&st->ops;
185 st->ops.st=st;
186 st->ops.check=rsa_sig_check;
187 st->loc=loc;
188
189 i=list_elem(args,0);
190 if (i) {
191 if (i->type!=t_string) {
39a6b1e2 192 cfgfatal(i->loc,"rsa-public","first argument must be a string\n");
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193 }
194 e=i->data.string;
195 if (mpz_init_set_str(&st->e,e,10)!=0) {
196 cfgfatal(i->loc,"rsa-public","encryption key \"%s\" is not a "
197 "decimal number string\n",e);
198 }
199 } else {
200 cfgfatal(loc,"rsa-public","you must provide an encryption key\n");
201 }
f15aefe4
MW
202 if (mpz_sizeinbase(&st->e, 256) > RSA_MAX_MODBYTES) {
203 cfgfatal(loc, "rsa-public", "implausibly large public exponent\n");
204 }
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205
206 i=list_elem(args,1);
207 if (i) {
208 if (i->type!=t_string) {
39a6b1e2 209 cfgfatal(i->loc,"rsa-public","second argument must be a string\n");
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210 }
211 n=i->data.string;
212 if (mpz_init_set_str(&st->n,n,10)!=0) {
213 cfgfatal(i->loc,"rsa-public","modulus \"%s\" is not a decimal "
214 "number string\n",n);
215 }
216 } else {
217 cfgfatal(loc,"rsa-public","you must provide a modulus\n");
218 }
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MW
219 if (mpz_sizeinbase(&st->n, 256) > RSA_MAX_MODBYTES) {
220 cfgfatal(loc, "rsa-public", "implausibly large modulus\n");
221 }
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222 return new_closure(&st->cl);
223}
224
4f5e39ec 225static uint32_t keyfile_get_int(struct cloc loc, FILE *f)
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226{
227 uint32_t r;
228 r=fgetc(f)<<24;
229 r|=fgetc(f)<<16;
230 r|=fgetc(f)<<8;
231 r|=fgetc(f);
4f5e39ec 232 cfgfile_postreadcheck(loc,f);
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233 return r;
234}
235
4f5e39ec 236static uint16_t keyfile_get_short(struct cloc loc, FILE *f)
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237{
238 uint16_t r;
239 r=fgetc(f)<<8;
240 r|=fgetc(f);
4f5e39ec 241 cfgfile_postreadcheck(loc,f);
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242 return r;
243}
244
245static list_t *rsapriv_apply(closure_t *self, struct cloc loc, dict_t *context,
246 list_t *args)
247{
248 struct rsapriv *st;
249 FILE *f;
fe5e9cc4 250 cstring_t filename;
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251 item_t *i;
252 long length;
253 uint8_t *b, *c;
254 int cipher_type;
fe5e9cc4 255 MP_INT e,d,iqmp,tmp,tmp2,tmp3;
3b83c932 256 bool_t valid;
2fe58dfd 257
b7886fd4 258 NEW(st);
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259 st->cl.description="rsapriv";
260 st->cl.type=CL_RSAPRIVKEY;
261 st->cl.apply=NULL;
262 st->cl.interface=&st->ops;
263 st->ops.st=st;
264 st->ops.sign=rsa_sign;
265 st->loc=loc;
266
267 /* Argument is filename pointing to SSH1 private key file */
268 i=list_elem(args,0);
269 if (i) {
270 if (i->type!=t_string) {
39a6b1e2 271 cfgfatal(i->loc,"rsa-public","first argument must be a string\n");
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272 }
273 filename=i->data.string;
274 } else {
fe5e9cc4 275 filename=NULL; /* Make compiler happy */
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276 cfgfatal(loc,"rsa-private","you must provide a filename\n");
277 }
278
279 f=fopen(filename,"rb");
280 if (!f) {
baa06aeb
SE
281 if (just_check_config) {
282 Message(M_WARNING,"rsa-private (%s:%d): cannot open keyfile "
283 "\"%s\"; assuming it's valid while we check the "
284 "rest of the configuration\n",loc.file,loc.line,filename);
285 goto assume_valid;
286 } else {
287 fatal_perror("rsa-private (%s:%d): cannot open file \"%s\"",
288 loc.file,loc.line,filename);
289 }
2fe58dfd
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290 }
291
292 /* Check that the ID string is correct */
293 length=strlen(AUTHFILE_ID_STRING)+1;
294 b=safe_malloc(length,"rsapriv_apply");
295 if (fread(b,length,1,f)!=1 || memcmp(b,AUTHFILE_ID_STRING,length)!=0) {
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296 cfgfatal_maybefile(f,loc,"rsa-private","failed to read magic ID"
297 " string from SSH1 private keyfile \"%s\"\n",
298 filename);
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299 }
300 free(b);
301
302 cipher_type=fgetc(f);
4f5e39ec 303 keyfile_get_int(loc,f); /* "Reserved data" */
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304 if (cipher_type != 0) {
305 cfgfatal(loc,"rsa-private","we don't support encrypted keyfiles\n");
306 }
307
308 /* Read the public key */
4f5e39ec
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309 keyfile_get_int(loc,f); /* Not sure what this is */
310 length=(keyfile_get_short(loc,f)+7)/8;
9941ae2e 311 if (length>RSA_MAX_MODBYTES) {
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SE
312 cfgfatal(loc,"rsa-private","implausible length %ld for modulus\n",
313 length);
314 }
315 b=safe_malloc(length,"rsapriv_apply");
316 if (fread(b,length,1,f) != 1) {
39a6b1e2 317 cfgfatal_maybefile(f,loc,"rsa-private","error reading modulus\n");
2fe58dfd
SE
318 }
319 mpz_init(&st->n);
320 read_mpbin(&st->n,b,length);
321 free(b);
4f5e39ec 322 length=(keyfile_get_short(loc,f)+7)/8;
9941ae2e 323 if (length>RSA_MAX_MODBYTES) {
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SE
324 cfgfatal(loc,"rsa-private","implausible length %ld for e\n",length);
325 }
326 b=safe_malloc(length,"rsapriv_apply");
327 if (fread(b,length,1,f)!=1) {
4f5e39ec 328 cfgfatal_maybefile(f,loc,"rsa-private","error reading e\n");
2fe58dfd
SE
329 }
330 mpz_init(&e);
331 read_mpbin(&e,b,length);
332 free(b);
333
4f5e39ec 334 length=keyfile_get_int(loc,f);
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335 if (length>1024) {
336 cfgfatal(loc,"rsa-private","implausibly long (%ld) key comment\n",
337 length);
338 }
339 c=safe_malloc(length+1,"rsapriv_apply");
340 if (fread(c,length,1,f)!=1) {
4f5e39ec 341 cfgfatal_maybefile(f,loc,"rsa-private","error reading key comment\n");
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342 }
343 c[length]=0;
344
345 /* Check that the next two pairs of characters are identical - the
346 keyfile is not encrypted, so they should be */
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347
348 if (keyfile_get_short(loc,f) != keyfile_get_short(loc,f)) {
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349 cfgfatal(loc,"rsa-private","corrupt keyfile\n");
350 }
351
352 /* Read d */
4f5e39ec 353 length=(keyfile_get_short(loc,f)+7)/8;
9941ae2e 354 if (length>RSA_MAX_MODBYTES) {
2fe58dfd
SE
355 cfgfatal(loc,"rsa-private","implausibly long (%ld) decryption key\n",
356 length);
357 }
358 b=safe_malloc(length,"rsapriv_apply");
359 if (fread(b,length,1,f)!=1) {
4f5e39ec
SE
360 cfgfatal_maybefile(f,loc,"rsa-private",
361 "error reading decryption key\n");
2fe58dfd 362 }
fe5e9cc4
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363 mpz_init(&d);
364 read_mpbin(&d,b,length);
365 free(b);
366 /* Read iqmp (inverse of q mod p) */
367 length=(keyfile_get_short(loc,f)+7)/8;
9941ae2e 368 if (length>RSA_MAX_MODBYTES) {
fe5e9cc4
SE
369 cfgfatal(loc,"rsa-private","implausibly long (%ld)"
370 " iqmp auxiliary value\n", length);
371 }
372 b=safe_malloc(length,"rsapriv_apply");
373 if (fread(b,length,1,f)!=1) {
374 cfgfatal_maybefile(f,loc,"rsa-private",
375 "error reading decryption key\n");
376 }
377 mpz_init(&iqmp);
378 read_mpbin(&iqmp,b,length);
379 free(b);
380 /* Read q (the smaller of the two primes) */
381 length=(keyfile_get_short(loc,f)+7)/8;
9941ae2e 382 if (length>RSA_MAX_MODBYTES) {
fe5e9cc4
SE
383 cfgfatal(loc,"rsa-private","implausibly long (%ld) q value\n",
384 length);
385 }
386 b=safe_malloc(length,"rsapriv_apply");
387 if (fread(b,length,1,f)!=1) {
388 cfgfatal_maybefile(f,loc,"rsa-private",
389 "error reading q value\n");
390 }
391 mpz_init(&st->q);
392 read_mpbin(&st->q,b,length);
393 free(b);
394 /* Read p (the larger of the two primes) */
395 length=(keyfile_get_short(loc,f)+7)/8;
9941ae2e 396 if (length>RSA_MAX_MODBYTES) {
fe5e9cc4
SE
397 cfgfatal(loc,"rsa-private","implausibly long (%ld) p value\n",
398 length);
399 }
400 b=safe_malloc(length,"rsapriv_apply");
401 if (fread(b,length,1,f)!=1) {
402 cfgfatal_maybefile(f,loc,"rsa-private",
403 "error reading p value\n");
404 }
405 mpz_init(&st->p);
406 read_mpbin(&st->p,b,length);
2fe58dfd
SE
407 free(b);
408
409 if (fclose(f)!=0) {
410 fatal_perror("rsa-private (%s:%d): fclose",loc.file,loc.line);
411 }
412
fe5e9cc4
SE
413 /*
414 * Now verify the validity of the key, and set up the auxiliary
415 * values for fast CRT signing.
416 */
3b83c932 417 valid=False;
70dc107b 418 i=list_elem(args,1);
3b83c932
SE
419 mpz_init(&tmp);
420 mpz_init(&tmp2);
421 mpz_init(&tmp3);
70dc107b
SE
422 if (i && i->type==t_bool && i->data.bool==False) {
423 Message(M_INFO,"rsa-private (%s:%d): skipping RSA key validity "
424 "check\n",loc.file,loc.line);
425 } else {
fe5e9cc4
SE
426 /* Verify that p*q is equal to n. */
427 mpz_mul(&tmp, &st->p, &st->q);
428 if (mpz_cmp(&tmp, &st->n) != 0)
429 goto done_checks;
430
431 /*
432 * Verify that d*e is congruent to 1 mod (p-1), and mod
433 * (q-1). This is equivalent to it being congruent to 1 mod
104e8e74
MW
434 * lambda(n) = lcm(p-1,q-1). The usual `textbook' condition,
435 * that d e == 1 (mod (p-1)(q-1)) is sufficient, but not
436 * actually necessary.
fe5e9cc4
SE
437 */
438 mpz_mul(&tmp, &d, &e);
439 mpz_sub_ui(&tmp2, &st->p, 1);
440 mpz_mod(&tmp3, &tmp, &tmp2);
441 if (mpz_cmp_si(&tmp3, 1) != 0)
442 goto done_checks;
443 mpz_sub_ui(&tmp2, &st->q, 1);
444 mpz_mod(&tmp3, &tmp, &tmp2);
445 if (mpz_cmp_si(&tmp3, 1) != 0)
446 goto done_checks;
447
448 /* Verify that q*iqmp is congruent to 1 mod p. */
449 mpz_mul(&tmp, &st->q, &iqmp);
450 mpz_mod(&tmp2, &tmp, &st->p);
451 if (mpz_cmp_si(&tmp2, 1) != 0)
452 goto done_checks;
2fe58dfd 453 }
3b83c932
SE
454 /* Now we know the key is valid (or we don't care). */
455 valid = True;
456
457 /*
458 * Now we compute auxiliary values dp, dq and w to allow us
459 * to use the CRT optimisation when signing.
460 *
461 * dp == d mod (p-1) so that a^dp == a^d mod p, for all a
462 * dq == d mod (q-1) similarly mod q
463 * w == iqmp * q so that w == 0 mod q, and w == 1 mod p
464 */
465 mpz_init(&st->dp);
466 mpz_init(&st->dq);
467 mpz_init(&st->w);
468 mpz_sub_ui(&tmp, &st->p, 1);
469 mpz_mod(&st->dp, &d, &tmp);
470 mpz_sub_ui(&tmp, &st->q, 1);
471 mpz_mod(&st->dq, &d, &tmp);
472 mpz_mul(&st->w, &iqmp, &st->q);
473
474done_checks:
475 if (!valid) {
476 cfgfatal(loc,"rsa-private","file \"%s\" does not contain a "
477 "valid RSA key!\n",filename);
478 }
479 mpz_clear(&tmp);
480 mpz_clear(&tmp2);
481 mpz_clear(&tmp3);
2fe58dfd
SE
482
483 free(c);
484 mpz_clear(&e);
fe5e9cc4
SE
485 mpz_clear(&d);
486 mpz_clear(&iqmp);
2fe58dfd 487
baa06aeb 488assume_valid:
2fe58dfd
SE
489 return new_closure(&st->cl);
490}
491
2fe58dfd
SE
492void rsa_module(dict_t *dict)
493{
494 add_closure(dict,"rsa-private",rsapriv_apply);
495 add_closure(dict,"rsa-public",rsapub_apply);
496}