2 * rsa.c: implementation of RSA with PKCS#1 padding
5 * This file is Free Software. It was originally written for secnet.
7 * Copyright 1995-2003 Stephen Early
8 * Copyright 2002-2014 Ian Jackson
9 * Copyright 2001 Simon Tatham
10 * Copyright 2013 Mark Wooding
12 * You may redistribute secnet as a whole and/or modify it under the
13 * terms of the GNU General Public License as published by the Free
14 * Software Foundation; either version 3, or (at your option) any
17 * You may redistribute this file and/or modify it under the terms of
18 * the GNU General Public License as published by the Free Software
19 * Foundation; either version 2, or (at your option) any later
22 * This software is distributed in the hope that it will be useful,
23 * but WITHOUT ANY WARRANTY; without even the implied warranty of
24 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
25 * GNU General Public License for more details.
27 * You should have received a copy of the GNU General Public License
28 * along with this software; if not, see
29 * https://www.gnu.org/licenses/gpl.html.
38 #include "unaligned.h"
40 #define AUTHFILE_ID_STRING "SSH PRIVATE KEY FILE FORMAT 1.1\n"
42 #define mpp(s,n) do { char *p = mpz_get_str(NULL,16,n); printf("%s 0x%sL\n", s, p); free(p); } while (0)
50 struct sigprivkey_if ops;
52 struct rsacommon common;
60 struct sigpubkey_if ops;
62 struct rsacommon common;
66 /* Sign data. NB data must be smaller than modulus */
68 #define RSA_MAX_MODBYTES 2048
69 /* The largest modulus I've seen is 15360 bits, which works out at 1920
70 * bytes. Using keys this big is quite implausible, but it doesn't cost us
71 * much to support them.
74 static const char *hexchars="0123456789abcdef";
76 static void rsa_sethash(struct rsacommon *c, struct hash_if *hash,
77 const struct hash_if **in_ops)
80 c->hashbuf=safe_malloc(hash->hlen, "generate_msg");
83 static void rsa_pub_sethash(void *sst, struct hash_if *hash)
85 struct rsapub *st=sst;
86 rsa_sethash(&st->common, hash, &st->ops.hash);
88 static void rsa_priv_sethash(void *sst, struct hash_if *hash)
90 struct rsapriv *st=sst;
91 rsa_sethash(&st->common, hash, &st->ops.hash);
94 static void emsa_pkcs1(MP_INT *n, MP_INT *m,
95 const uint8_t *data, int32_t datalen)
97 char buff[2*RSA_MAX_MODBYTES + 1];
100 /* RSA PKCS#1 v1.5 signature padding:
102 * <------------ msize hex digits ---------->
104 * 00 01 ff ff .... ff ff 00 vv vv vv .... vv
108 * = datalen*2 hex digits
110 * NB that according to PKCS#1 v1.5 we're supposed to include a
111 * hash function OID in the data. We don't do that (because we
112 * don't have the hash function OID to hand here), thus violating
113 * the spec in a way that affects interop but not security.
118 msize=mpz_sizeinbase(n, 16);
120 if (datalen*2+6>=msize) {
121 fatal("rsa: message too big");
126 for (i=0; i<datalen; i++) {
127 buff[msize+(-datalen+i)*2]=hexchars[(data[i]&0xf0)>>4];
128 buff[msize+(-datalen+i)*2+1]=hexchars[data[i]&0xf];
131 buff[msize-datalen*2-2]= '0';
132 buff[msize-datalen*2-1]= '0';
134 for (i=4; i<msize-datalen*2-2; i++)
139 mpz_set_str(m, buff, 16);
142 static bool_t rsa_sign(void *sst, uint8_t *data, int32_t datalen,
143 struct buffer_if *msg)
145 struct rsapriv *st=sst;
146 MP_INT a, b, u, v, tmp, tmp2;
147 string_t signature = 0;
153 hash_hash(st->ops.hash,data,datalen,st->common.hashbuf);
154 /* Construct the message representative. */
155 emsa_pkcs1(&st->n, &a, st->common.hashbuf, st->ops.hash->hlen);
158 * Produce an RSA signature (a^d mod n) using the Chinese
159 * Remainder Theorem. We compute:
161 * u = a^dp mod p (== a^d mod p, since dp == d mod (p-1))
162 * v = a^dq mod q (== a^d mod q, similarly)
164 * We also know w == iqmp * q, which has the property that w ==
165 * 0 mod q and w == 1 mod p. So (1-w) has the reverse property
166 * (congruent to 0 mod p and to 1 mod q). Hence we now compute
168 * b = w * u + (1-w) * v
171 * so that b is congruent to a^d both mod p and mod q. Hence b,
172 * reduced mod n, is the required signature.
179 mpz_powm_sec(&u, &a, &st->dp, &st->p);
180 mpz_powm_sec(&v, &a, &st->dq, &st->q);
181 mpz_sub(&tmp, &u, &v);
182 mpz_mul(&tmp2, &tmp, &st->w);
183 mpz_add(&tmp, &tmp2, &v);
184 mpz_mod(&b, &tmp, &st->n);
191 signature=write_mpstring(&b);
193 uint8_t *op = buf_append(msg,2);
194 if (!op) { ok=False; goto out; }
195 size_t l = strlen(signature);
198 op = buf_append(msg,l);
199 if (!op) { ok=False; goto out; }
200 memcpy(op, signature, l);
211 static bool_t rsa_sig_unpick(void *sst, struct buffer_if *msg,
212 struct alg_msg_data *sig)
214 uint8_t *lp = buf_unprepend(msg, 2);
215 if (!lp) return False;
216 sig->len = get_uint16(lp);
217 sig->start = buf_unprepend(msg, sig->len);
218 if (!sig->start) return False;
220 /* In `rsa_sig_check' below, we assume that we can write a nul
221 * terminator following the signature. Make sure there's enough space.
223 if (msg->start >= msg->base + msg->alloclen)
229 static sig_checksig_fn rsa_sig_check;
230 static bool_t rsa_sig_check(void *sst, uint8_t *data, int32_t datalen,
231 const struct alg_msg_data *sig)
233 struct rsapub *st=sst;
241 hash_hash(st->ops.hash,data,datalen,st->common.hashbuf);
242 emsa_pkcs1(&st->n, &a, st->common.hashbuf, st->ops.hash->hlen);
244 /* Terminate signature with a '0' - already checked that this will fit */
245 int save = sig->start[sig->len];
246 sig->start[sig->len] = 0;
247 mpz_set_str(&b, sig->start, 16);
248 sig->start[sig->len] = save;
250 mpz_powm(&c, &b, &st->e, &st->n);
252 ok=(mpz_cmp(&a, &c)==0);
261 static list_t *rsapub_apply(closure_t *self, struct cloc loc, dict_t *context,
269 st->cl.description="rsapub";
270 st->cl.type=CL_SIGPUBKEY;
272 st->cl.interface=&st->ops;
274 st->ops.sethash=rsa_pub_sethash;
275 st->common.hashbuf=NULL;
276 st->ops.unpick=rsa_sig_unpick;
277 st->ops.check=rsa_sig_check;
283 if (i->type!=t_string) {
284 cfgfatal(i->loc,"rsa-public","first argument must be a string\n");
287 if (mpz_init_set_str(&st->e,e,10)!=0) {
288 cfgfatal(i->loc,"rsa-public","encryption key \"%s\" is not a "
289 "decimal number string\n",e);
292 cfgfatal(loc,"rsa-public","you must provide an encryption key\n");
294 if (mpz_sizeinbase(&st->e, 256) > RSA_MAX_MODBYTES) {
295 cfgfatal(loc, "rsa-public", "implausibly large public exponent\n");
300 if (i->type!=t_string) {
301 cfgfatal(i->loc,"rsa-public","second argument must be a string\n");
304 if (mpz_init_set_str(&st->n,n,10)!=0) {
305 cfgfatal(i->loc,"rsa-public","modulus \"%s\" is not a decimal "
306 "number string\n",n);
309 cfgfatal(loc,"rsa-public","you must provide a modulus\n");
311 if (mpz_sizeinbase(&st->n, 256) > RSA_MAX_MODBYTES) {
312 cfgfatal(loc, "rsa-public", "implausibly large modulus\n");
314 return new_closure(&st->cl);
317 static uint32_t keyfile_get_int(struct cloc loc, FILE *f)
324 cfgfile_postreadcheck(loc,f);
328 static uint16_t keyfile_get_short(struct cloc loc, FILE *f)
333 cfgfile_postreadcheck(loc,f);
337 static list_t *rsapriv_apply(closure_t *self, struct cloc loc, dict_t *context,
347 MP_INT e,d,iqmp,tmp,tmp2,tmp3;
351 st->cl.description="rsapriv";
352 st->cl.type=CL_SIGPRIVKEY;
354 st->cl.interface=&st->ops;
356 st->ops.sethash=rsa_priv_sethash;
357 st->common.hashbuf=NULL;
358 st->ops.sign=rsa_sign;
362 /* Argument is filename pointing to SSH1 private key file */
365 if (i->type!=t_string) {
366 cfgfatal(i->loc,"rsa-private","first argument must be a string\n");
368 filename=i->data.string;
370 filename=NULL; /* Make compiler happy */
371 cfgfatal(loc,"rsa-private","you must provide a filename\n");
374 f=fopen(filename,"rb");
376 if (just_check_config) {
377 Message(M_WARNING,"rsa-private (%s:%d): cannot open keyfile "
378 "\"%s\"; assuming it's valid while we check the "
379 "rest of the configuration\n",loc.file,loc.line,filename);
382 fatal_perror("rsa-private (%s:%d): cannot open file \"%s\"",
383 loc.file,loc.line,filename);
387 /* Check that the ID string is correct */
388 length=strlen(AUTHFILE_ID_STRING)+1;
389 b=safe_malloc(length,"rsapriv_apply");
390 if (fread(b,length,1,f)!=1 || memcmp(b,AUTHFILE_ID_STRING,length)!=0) {
391 cfgfatal_maybefile(f,loc,"rsa-private","failed to read magic ID"
392 " string from SSH1 private keyfile \"%s\"\n",
397 cipher_type=fgetc(f);
398 keyfile_get_int(loc,f); /* "Reserved data" */
399 if (cipher_type != 0) {
400 cfgfatal(loc,"rsa-private","we don't support encrypted keyfiles\n");
403 /* Read the public key */
404 keyfile_get_int(loc,f); /* Not sure what this is */
405 length=(keyfile_get_short(loc,f)+7)/8;
406 if (length>RSA_MAX_MODBYTES) {
407 cfgfatal(loc,"rsa-private","implausible length %ld for modulus\n",
410 b=safe_malloc(length,"rsapriv_apply");
411 if (fread(b,length,1,f) != 1) {
412 cfgfatal_maybefile(f,loc,"rsa-private","error reading modulus\n");
415 read_mpbin(&st->n,b,length);
417 length=(keyfile_get_short(loc,f)+7)/8;
418 if (length>RSA_MAX_MODBYTES) {
419 cfgfatal(loc,"rsa-private","implausible length %ld for e\n",length);
421 b=safe_malloc(length,"rsapriv_apply");
422 if (fread(b,length,1,f)!=1) {
423 cfgfatal_maybefile(f,loc,"rsa-private","error reading e\n");
426 read_mpbin(&e,b,length);
429 length=keyfile_get_int(loc,f);
431 cfgfatal(loc,"rsa-private","implausibly long (%ld) key comment\n",
434 c=safe_malloc(length+1,"rsapriv_apply");
435 if (fread(c,length,1,f)!=1) {
436 cfgfatal_maybefile(f,loc,"rsa-private","error reading key comment\n");
440 /* Check that the next two pairs of characters are identical - the
441 keyfile is not encrypted, so they should be */
443 if (keyfile_get_short(loc,f) != keyfile_get_short(loc,f)) {
444 cfgfatal(loc,"rsa-private","corrupt keyfile\n");
448 length=(keyfile_get_short(loc,f)+7)/8;
449 if (length>RSA_MAX_MODBYTES) {
450 cfgfatal(loc,"rsa-private","implausibly long (%ld) decryption key\n",
453 b=safe_malloc(length,"rsapriv_apply");
454 if (fread(b,length,1,f)!=1) {
455 cfgfatal_maybefile(f,loc,"rsa-private",
456 "error reading decryption key\n");
459 read_mpbin(&d,b,length);
461 /* Read iqmp (inverse of q mod p) */
462 length=(keyfile_get_short(loc,f)+7)/8;
463 if (length>RSA_MAX_MODBYTES) {
464 cfgfatal(loc,"rsa-private","implausibly long (%ld)"
465 " iqmp auxiliary value\n", length);
467 b=safe_malloc(length,"rsapriv_apply");
468 if (fread(b,length,1,f)!=1) {
469 cfgfatal_maybefile(f,loc,"rsa-private",
470 "error reading decryption key\n");
473 read_mpbin(&iqmp,b,length);
475 /* Read q (the smaller of the two primes) */
476 length=(keyfile_get_short(loc,f)+7)/8;
477 if (length>RSA_MAX_MODBYTES) {
478 cfgfatal(loc,"rsa-private","implausibly long (%ld) q value\n",
481 b=safe_malloc(length,"rsapriv_apply");
482 if (fread(b,length,1,f)!=1) {
483 cfgfatal_maybefile(f,loc,"rsa-private",
484 "error reading q value\n");
487 read_mpbin(&st->q,b,length);
489 /* Read p (the larger of the two primes) */
490 length=(keyfile_get_short(loc,f)+7)/8;
491 if (length>RSA_MAX_MODBYTES) {
492 cfgfatal(loc,"rsa-private","implausibly long (%ld) p value\n",
495 b=safe_malloc(length,"rsapriv_apply");
496 if (fread(b,length,1,f)!=1) {
497 cfgfatal_maybefile(f,loc,"rsa-private",
498 "error reading p value\n");
501 read_mpbin(&st->p,b,length);
505 fatal_perror("rsa-private (%s:%d): fclose",loc.file,loc.line);
509 * Now verify the validity of the key, and set up the auxiliary
510 * values for fast CRT signing.
517 if (i && i->type==t_bool && i->data.bool==False) {
518 Message(M_INFO,"rsa-private (%s:%d): skipping RSA key validity "
519 "check\n",loc.file,loc.line);
521 /* Verify that p*q is equal to n. */
522 mpz_mul(&tmp, &st->p, &st->q);
523 if (mpz_cmp(&tmp, &st->n) != 0)
527 * Verify that d*e is congruent to 1 mod (p-1), and mod
528 * (q-1). This is equivalent to it being congruent to 1 mod
529 * lambda(n) = lcm(p-1,q-1). The usual `textbook' condition,
530 * that d e == 1 (mod (p-1)(q-1)) is sufficient, but not
531 * actually necessary.
533 mpz_mul(&tmp, &d, &e);
534 mpz_sub_ui(&tmp2, &st->p, 1);
535 mpz_mod(&tmp3, &tmp, &tmp2);
536 if (mpz_cmp_si(&tmp3, 1) != 0)
538 mpz_sub_ui(&tmp2, &st->q, 1);
539 mpz_mod(&tmp3, &tmp, &tmp2);
540 if (mpz_cmp_si(&tmp3, 1) != 0)
543 /* Verify that q*iqmp is congruent to 1 mod p. */
544 mpz_mul(&tmp, &st->q, &iqmp);
545 mpz_mod(&tmp2, &tmp, &st->p);
546 if (mpz_cmp_si(&tmp2, 1) != 0)
549 /* Now we know the key is valid (or we don't care). */
553 * Now we compute auxiliary values dp, dq and w to allow us
554 * to use the CRT optimisation when signing.
556 * dp == d mod (p-1) so that a^dp == a^d mod p, for all a
557 * dq == d mod (q-1) similarly mod q
558 * w == iqmp * q so that w == 0 mod q, and w == 1 mod p
563 mpz_sub_ui(&tmp, &st->p, 1);
564 mpz_mod(&st->dp, &d, &tmp);
565 mpz_sub_ui(&tmp, &st->q, 1);
566 mpz_mod(&st->dq, &d, &tmp);
567 mpz_mul(&st->w, &iqmp, &st->q);
571 cfgfatal(loc,"rsa-private","file \"%s\" does not contain a "
572 "valid RSA key!\n",filename);
584 return new_closure(&st->cl);
587 void rsa_module(dict_t *dict)
589 add_closure(dict,"rsa-private",rsapriv_apply);
590 add_closure(dict,"rsa-public",rsapub_apply);