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)
45 struct hash_if *hashi;
51 struct sigprivkey_if ops;
53 struct rsacommon common;
61 struct sigpubkey_if ops;
63 struct rsacommon common;
67 /* Sign data. NB data must be smaller than modulus */
69 #define RSA_MAX_MODBYTES 2048
70 /* The largest modulus I've seen is 15360 bits, which works out at 1920
71 * bytes. Using keys this big is quite implausible, but it doesn't cost us
72 * much to support them.
75 static const char *hexchars="0123456789abcdef";
77 static void rsa_sethash(struct rsacommon *c, struct hash_if *hash)
80 c->hashbuf=safe_malloc(hash->len, "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);
88 static void rsa_priv_sethash(void *sst, struct hash_if *hash)
90 struct rsapriv *st=sst;
91 rsa_sethash(&st->common, hash);
93 static void rsa_hash(struct rsacommon *c, const uint8_t *buf, int32_t len)
95 void *hst=c->hashi->init();
96 c->hashi->update(hst,buf,len);
97 c->hashi->final(hst,c->hashbuf);
100 static void emsa_pkcs1(MP_INT *n, MP_INT *m,
101 const uint8_t *data, int32_t datalen)
103 char buff[2*RSA_MAX_MODBYTES + 1];
106 /* RSA PKCS#1 v1.5 signature padding:
108 * <------------ msize hex digits ---------->
110 * 00 01 ff ff .... ff ff 00 vv vv vv .... vv
114 * = datalen*2 hex digits
116 * NB that according to PKCS#1 v1.5 we're supposed to include a
117 * hash function OID in the data. We don't do that (because we
118 * don't have the hash function OID to hand here), thus violating
119 * the spec in a way that affects interop but not security.
124 msize=mpz_sizeinbase(n, 16);
126 if (datalen*2+6>=msize) {
127 fatal("rsa_sign: message too big");
132 for (i=0; i<datalen; i++) {
133 buff[msize+(-datalen+i)*2]=hexchars[(data[i]&0xf0)>>4];
134 buff[msize+(-datalen+i)*2+1]=hexchars[data[i]&0xf];
137 buff[msize-datalen*2-2]= '0';
138 buff[msize-datalen*2-1]= '0';
140 for (i=4; i<msize-datalen*2-2; i++)
145 mpz_set_str(m, buff, 16);
148 static bool_t rsa_sign(void *sst, uint8_t *data, int32_t datalen,
149 struct buffer_if *msg)
151 struct rsapriv *st=sst;
152 MP_INT a, b, u, v, tmp, tmp2;
153 string_t signature = 0;
159 rsa_hash(&st->common,data,datalen);
160 /* Construct the message representative. */
161 emsa_pkcs1(&st->n, &a, st->common.hashbuf, st->common.hashi->len);
164 * Produce an RSA signature (a^d mod n) using the Chinese
165 * Remainder Theorem. We compute:
167 * u = a^dp mod p (== a^d mod p, since dp == d mod (p-1))
168 * v = a^dq mod q (== a^d mod q, similarly)
170 * We also know w == iqmp * q, which has the property that w ==
171 * 0 mod q and w == 1 mod p. So (1-w) has the reverse property
172 * (congruent to 0 mod p and to 1 mod q). Hence we now compute
174 * b = w * u + (1-w) * v
177 * so that b is congruent to a^d both mod p and mod q. Hence b,
178 * reduced mod n, is the required signature.
185 mpz_powm_sec(&u, &a, &st->dp, &st->p);
186 mpz_powm_sec(&v, &a, &st->dq, &st->q);
187 mpz_sub(&tmp, &u, &v);
188 mpz_mul(&tmp2, &tmp, &st->w);
189 mpz_add(&tmp, &tmp2, &v);
190 mpz_mod(&b, &tmp, &st->n);
197 signature=write_mpstring(&b);
199 uint8_t *op = buf_append(msg,2);
200 if (!op) { ok=False; goto out; }
201 size_t l = strlen(signature);
204 op = buf_append(msg,l);
205 if (!op) { ok=False; goto out; }
206 memcpy(op, signature, l);
217 static bool_t rsa_sig_unpick(void *sst, struct buffer_if *msg,
218 struct alg_msg_data *sig)
220 uint8_t *lp = buf_unprepend(msg, 2);
221 if (!lp) return False;
222 sig->siglen = get_uint16(lp);
223 sig->sigstart = buf_unprepend(msg, sig->siglen);
224 if (!sig->sigstart) return False;
226 /* In `rsa_sig_check' below, we assume that we can write a nul
227 * terminator following the signature. Make sure there's enough space.
229 if (msg->start >= msg->base + msg->alloclen)
235 static sig_checksig_fn rsa_sig_check;
236 static bool_t rsa_sig_check(void *sst, uint8_t *data, int32_t datalen,
237 const struct alg_msg_data *sig)
239 struct rsapub *st=sst;
247 rsa_hash(&st->common,data,datalen);
248 emsa_pkcs1(&st->n, &a, st->common.hashbuf, st->common.hashi->len);
250 /* Terminate signature with a '0' - already checked that this will fit */
251 int save = sig->sigstart[sig->siglen];
252 sig->sigstart[sig->siglen] = 0;
253 mpz_set_str(&b, sig->sigstart, 16);
254 sig->sigstart[sig->siglen] = save;
256 mpz_powm(&c, &b, &st->e, &st->n);
258 ok=(mpz_cmp(&a, &c)==0);
267 static list_t *rsapub_apply(closure_t *self, struct cloc loc, dict_t *context,
275 st->cl.description="rsapub";
276 st->cl.type=CL_SIGPUBKEY;
278 st->cl.interface=&st->ops;
280 st->ops.sethash=rsa_pub_sethash;
281 st->common.hashbuf=NULL;
282 st->ops.unpick=rsa_sig_unpick;
283 st->ops.check=rsa_sig_check;
288 if (i->type!=t_string) {
289 cfgfatal(i->loc,"rsa-public","first argument must be a string\n");
292 if (mpz_init_set_str(&st->e,e,10)!=0) {
293 cfgfatal(i->loc,"rsa-public","encryption key \"%s\" is not a "
294 "decimal number string\n",e);
297 cfgfatal(loc,"rsa-public","you must provide an encryption key\n");
299 if (mpz_sizeinbase(&st->e, 256) > RSA_MAX_MODBYTES) {
300 cfgfatal(loc, "rsa-public", "implausibly large public exponent\n");
305 if (i->type!=t_string) {
306 cfgfatal(i->loc,"rsa-public","second argument must be a string\n");
309 if (mpz_init_set_str(&st->n,n,10)!=0) {
310 cfgfatal(i->loc,"rsa-public","modulus \"%s\" is not a decimal "
311 "number string\n",n);
314 cfgfatal(loc,"rsa-public","you must provide a modulus\n");
316 if (mpz_sizeinbase(&st->n, 256) > RSA_MAX_MODBYTES) {
317 cfgfatal(loc, "rsa-public", "implausibly large modulus\n");
319 return new_closure(&st->cl);
322 static uint32_t keyfile_get_int(struct cloc loc, FILE *f)
329 cfgfile_postreadcheck(loc,f);
333 static uint16_t keyfile_get_short(struct cloc loc, FILE *f)
338 cfgfile_postreadcheck(loc,f);
342 static list_t *rsapriv_apply(closure_t *self, struct cloc loc, dict_t *context,
352 MP_INT e,d,iqmp,tmp,tmp2,tmp3;
356 st->cl.description="rsapriv";
357 st->cl.type=CL_SIGPRIVKEY;
359 st->cl.interface=&st->ops;
361 st->ops.sethash=rsa_priv_sethash;
362 st->common.hashbuf=NULL;
363 st->ops.sign=rsa_sign;
366 /* Argument is filename pointing to SSH1 private key file */
369 if (i->type!=t_string) {
370 cfgfatal(i->loc,"rsa-private","first argument must be a string\n");
372 filename=i->data.string;
374 filename=NULL; /* Make compiler happy */
375 cfgfatal(loc,"rsa-private","you must provide a filename\n");
378 f=fopen(filename,"rb");
380 if (just_check_config) {
381 Message(M_WARNING,"rsa-private (%s:%d): cannot open keyfile "
382 "\"%s\"; assuming it's valid while we check the "
383 "rest of the configuration\n",loc.file,loc.line,filename);
386 fatal_perror("rsa-private (%s:%d): cannot open file \"%s\"",
387 loc.file,loc.line,filename);
391 /* Check that the ID string is correct */
392 length=strlen(AUTHFILE_ID_STRING)+1;
393 b=safe_malloc(length,"rsapriv_apply");
394 if (fread(b,length,1,f)!=1 || memcmp(b,AUTHFILE_ID_STRING,length)!=0) {
395 cfgfatal_maybefile(f,loc,"rsa-private","failed to read magic ID"
396 " string from SSH1 private keyfile \"%s\"\n",
401 cipher_type=fgetc(f);
402 keyfile_get_int(loc,f); /* "Reserved data" */
403 if (cipher_type != 0) {
404 cfgfatal(loc,"rsa-private","we don't support encrypted keyfiles\n");
407 /* Read the public key */
408 keyfile_get_int(loc,f); /* Not sure what this is */
409 length=(keyfile_get_short(loc,f)+7)/8;
410 if (length>RSA_MAX_MODBYTES) {
411 cfgfatal(loc,"rsa-private","implausible length %ld for modulus\n",
414 b=safe_malloc(length,"rsapriv_apply");
415 if (fread(b,length,1,f) != 1) {
416 cfgfatal_maybefile(f,loc,"rsa-private","error reading modulus\n");
419 read_mpbin(&st->n,b,length);
421 length=(keyfile_get_short(loc,f)+7)/8;
422 if (length>RSA_MAX_MODBYTES) {
423 cfgfatal(loc,"rsa-private","implausible length %ld for e\n",length);
425 b=safe_malloc(length,"rsapriv_apply");
426 if (fread(b,length,1,f)!=1) {
427 cfgfatal_maybefile(f,loc,"rsa-private","error reading e\n");
430 read_mpbin(&e,b,length);
433 length=keyfile_get_int(loc,f);
435 cfgfatal(loc,"rsa-private","implausibly long (%ld) key comment\n",
438 c=safe_malloc(length+1,"rsapriv_apply");
439 if (fread(c,length,1,f)!=1) {
440 cfgfatal_maybefile(f,loc,"rsa-private","error reading key comment\n");
444 /* Check that the next two pairs of characters are identical - the
445 keyfile is not encrypted, so they should be */
447 if (keyfile_get_short(loc,f) != keyfile_get_short(loc,f)) {
448 cfgfatal(loc,"rsa-private","corrupt keyfile\n");
452 length=(keyfile_get_short(loc,f)+7)/8;
453 if (length>RSA_MAX_MODBYTES) {
454 cfgfatal(loc,"rsa-private","implausibly long (%ld) decryption key\n",
457 b=safe_malloc(length,"rsapriv_apply");
458 if (fread(b,length,1,f)!=1) {
459 cfgfatal_maybefile(f,loc,"rsa-private",
460 "error reading decryption key\n");
463 read_mpbin(&d,b,length);
465 /* Read iqmp (inverse of q mod p) */
466 length=(keyfile_get_short(loc,f)+7)/8;
467 if (length>RSA_MAX_MODBYTES) {
468 cfgfatal(loc,"rsa-private","implausibly long (%ld)"
469 " iqmp auxiliary value\n", length);
471 b=safe_malloc(length,"rsapriv_apply");
472 if (fread(b,length,1,f)!=1) {
473 cfgfatal_maybefile(f,loc,"rsa-private",
474 "error reading decryption key\n");
477 read_mpbin(&iqmp,b,length);
479 /* Read q (the smaller of the two primes) */
480 length=(keyfile_get_short(loc,f)+7)/8;
481 if (length>RSA_MAX_MODBYTES) {
482 cfgfatal(loc,"rsa-private","implausibly long (%ld) q value\n",
485 b=safe_malloc(length,"rsapriv_apply");
486 if (fread(b,length,1,f)!=1) {
487 cfgfatal_maybefile(f,loc,"rsa-private",
488 "error reading q value\n");
491 read_mpbin(&st->q,b,length);
493 /* Read p (the larger of the two primes) */
494 length=(keyfile_get_short(loc,f)+7)/8;
495 if (length>RSA_MAX_MODBYTES) {
496 cfgfatal(loc,"rsa-private","implausibly long (%ld) p value\n",
499 b=safe_malloc(length,"rsapriv_apply");
500 if (fread(b,length,1,f)!=1) {
501 cfgfatal_maybefile(f,loc,"rsa-private",
502 "error reading p value\n");
505 read_mpbin(&st->p,b,length);
509 fatal_perror("rsa-private (%s:%d): fclose",loc.file,loc.line);
513 * Now verify the validity of the key, and set up the auxiliary
514 * values for fast CRT signing.
521 if (i && i->type==t_bool && i->data.bool==False) {
522 Message(M_INFO,"rsa-private (%s:%d): skipping RSA key validity "
523 "check\n",loc.file,loc.line);
525 /* Verify that p*q is equal to n. */
526 mpz_mul(&tmp, &st->p, &st->q);
527 if (mpz_cmp(&tmp, &st->n) != 0)
531 * Verify that d*e is congruent to 1 mod (p-1), and mod
532 * (q-1). This is equivalent to it being congruent to 1 mod
533 * lambda(n) = lcm(p-1,q-1). The usual `textbook' condition,
534 * that d e == 1 (mod (p-1)(q-1)) is sufficient, but not
535 * actually necessary.
537 mpz_mul(&tmp, &d, &e);
538 mpz_sub_ui(&tmp2, &st->p, 1);
539 mpz_mod(&tmp3, &tmp, &tmp2);
540 if (mpz_cmp_si(&tmp3, 1) != 0)
542 mpz_sub_ui(&tmp2, &st->q, 1);
543 mpz_mod(&tmp3, &tmp, &tmp2);
544 if (mpz_cmp_si(&tmp3, 1) != 0)
547 /* Verify that q*iqmp is congruent to 1 mod p. */
548 mpz_mul(&tmp, &st->q, &iqmp);
549 mpz_mod(&tmp2, &tmp, &st->p);
550 if (mpz_cmp_si(&tmp2, 1) != 0)
553 /* Now we know the key is valid (or we don't care). */
557 * Now we compute auxiliary values dp, dq and w to allow us
558 * to use the CRT optimisation when signing.
560 * dp == d mod (p-1) so that a^dp == a^d mod p, for all a
561 * dq == d mod (q-1) similarly mod q
562 * w == iqmp * q so that w == 0 mod q, and w == 1 mod p
567 mpz_sub_ui(&tmp, &st->p, 1);
568 mpz_mod(&st->dp, &d, &tmp);
569 mpz_sub_ui(&tmp, &st->q, 1);
570 mpz_mod(&st->dq, &d, &tmp);
571 mpz_mul(&st->w, &iqmp, &st->q);
575 cfgfatal(loc,"rsa-private","file \"%s\" does not contain a "
576 "valid RSA key!\n",filename);
588 return new_closure(&st->cl);
591 void rsa_module(dict_t *dict)
593 add_closure(dict,"rsa-private",rsapriv_apply);
594 add_closure(dict,"rsa-public",rsapub_apply);