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->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);
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 uint8_t hst[c->hashi->slen];
97 c->hashi->update(hst,buf,len);
98 c->hashi->final(hst,c->hashbuf);
101 static void emsa_pkcs1(MP_INT *n, MP_INT *m,
102 const uint8_t *data, int32_t datalen)
104 char buff[2*RSA_MAX_MODBYTES + 1];
107 /* RSA PKCS#1 v1.5 signature padding:
109 * <------------ msize hex digits ---------->
111 * 00 01 ff ff .... ff ff 00 vv vv vv .... vv
115 * = datalen*2 hex digits
117 * NB that according to PKCS#1 v1.5 we're supposed to include a
118 * hash function OID in the data. We don't do that (because we
119 * don't have the hash function OID to hand here), thus violating
120 * the spec in a way that affects interop but not security.
125 msize=mpz_sizeinbase(n, 16);
127 if (datalen*2+6>=msize) {
128 fatal("rsa_sign: message too big");
133 for (i=0; i<datalen; i++) {
134 buff[msize+(-datalen+i)*2]=hexchars[(data[i]&0xf0)>>4];
135 buff[msize+(-datalen+i)*2+1]=hexchars[data[i]&0xf];
138 buff[msize-datalen*2-2]= '0';
139 buff[msize-datalen*2-1]= '0';
141 for (i=4; i<msize-datalen*2-2; i++)
146 mpz_set_str(m, buff, 16);
149 static bool_t rsa_sign(void *sst, uint8_t *data, int32_t datalen,
150 struct buffer_if *msg)
152 struct rsapriv *st=sst;
153 MP_INT a, b, u, v, tmp, tmp2;
154 string_t signature = 0;
160 rsa_hash(&st->common,data,datalen);
161 /* Construct the message representative. */
162 emsa_pkcs1(&st->n, &a, st->common.hashbuf, st->common.hashi->hlen);
165 * Produce an RSA signature (a^d mod n) using the Chinese
166 * Remainder Theorem. We compute:
168 * u = a^dp mod p (== a^d mod p, since dp == d mod (p-1))
169 * v = a^dq mod q (== a^d mod q, similarly)
171 * We also know w == iqmp * q, which has the property that w ==
172 * 0 mod q and w == 1 mod p. So (1-w) has the reverse property
173 * (congruent to 0 mod p and to 1 mod q). Hence we now compute
175 * b = w * u + (1-w) * v
178 * so that b is congruent to a^d both mod p and mod q. Hence b,
179 * reduced mod n, is the required signature.
186 mpz_powm_sec(&u, &a, &st->dp, &st->p);
187 mpz_powm_sec(&v, &a, &st->dq, &st->q);
188 mpz_sub(&tmp, &u, &v);
189 mpz_mul(&tmp2, &tmp, &st->w);
190 mpz_add(&tmp, &tmp2, &v);
191 mpz_mod(&b, &tmp, &st->n);
198 signature=write_mpstring(&b);
200 uint8_t *op = buf_append(msg,2);
201 if (!op) { ok=False; goto out; }
202 size_t l = strlen(signature);
205 op = buf_append(msg,l);
206 if (!op) { ok=False; goto out; }
207 memcpy(op, signature, l);
218 static bool_t rsa_sig_unpick(void *sst, struct buffer_if *msg,
219 struct alg_msg_data *sig)
221 uint8_t *lp = buf_unprepend(msg, 2);
222 if (!lp) return False;
223 sig->siglen = get_uint16(lp);
224 sig->sigstart = buf_unprepend(msg, sig->siglen);
225 if (!sig->sigstart) return False;
227 /* In `rsa_sig_check' below, we assume that we can write a nul
228 * terminator following the signature. Make sure there's enough space.
230 if (msg->start >= msg->base + msg->alloclen)
236 static sig_checksig_fn rsa_sig_check;
237 static bool_t rsa_sig_check(void *sst, uint8_t *data, int32_t datalen,
238 const struct alg_msg_data *sig)
240 struct rsapub *st=sst;
248 rsa_hash(&st->common,data,datalen);
249 emsa_pkcs1(&st->n, &a, st->common.hashbuf, st->common.hashi->hlen);
251 /* Terminate signature with a '0' - already checked that this will fit */
252 int save = sig->sigstart[sig->siglen];
253 sig->sigstart[sig->siglen] = 0;
254 mpz_set_str(&b, sig->sigstart, 16);
255 sig->sigstart[sig->siglen] = save;
257 mpz_powm(&c, &b, &st->e, &st->n);
259 ok=(mpz_cmp(&a, &c)==0);
268 static list_t *rsapub_apply(closure_t *self, struct cloc loc, dict_t *context,
276 st->cl.description="rsapub";
277 st->cl.type=CL_SIGPUBKEY;
279 st->cl.interface=&st->ops;
281 st->ops.sethash=rsa_pub_sethash;
282 st->common.hashbuf=NULL;
283 st->ops.unpick=rsa_sig_unpick;
284 st->ops.check=rsa_sig_check;
289 if (i->type!=t_string) {
290 cfgfatal(i->loc,"rsa-public","first argument must be a string\n");
293 if (mpz_init_set_str(&st->e,e,10)!=0) {
294 cfgfatal(i->loc,"rsa-public","encryption key \"%s\" is not a "
295 "decimal number string\n",e);
298 cfgfatal(loc,"rsa-public","you must provide an encryption key\n");
300 if (mpz_sizeinbase(&st->e, 256) > RSA_MAX_MODBYTES) {
301 cfgfatal(loc, "rsa-public", "implausibly large public exponent\n");
306 if (i->type!=t_string) {
307 cfgfatal(i->loc,"rsa-public","second argument must be a string\n");
310 if (mpz_init_set_str(&st->n,n,10)!=0) {
311 cfgfatal(i->loc,"rsa-public","modulus \"%s\" is not a decimal "
312 "number string\n",n);
315 cfgfatal(loc,"rsa-public","you must provide a modulus\n");
317 if (mpz_sizeinbase(&st->n, 256) > RSA_MAX_MODBYTES) {
318 cfgfatal(loc, "rsa-public", "implausibly large modulus\n");
320 return new_closure(&st->cl);
323 static uint32_t keyfile_get_int(struct cloc loc, FILE *f)
330 cfgfile_postreadcheck(loc,f);
334 static uint16_t keyfile_get_short(struct cloc loc, FILE *f)
339 cfgfile_postreadcheck(loc,f);
343 static list_t *rsapriv_apply(closure_t *self, struct cloc loc, dict_t *context,
353 MP_INT e,d,iqmp,tmp,tmp2,tmp3;
357 st->cl.description="rsapriv";
358 st->cl.type=CL_SIGPRIVKEY;
360 st->cl.interface=&st->ops;
362 st->ops.sethash=rsa_priv_sethash;
363 st->common.hashbuf=NULL;
364 st->ops.sign=rsa_sign;
367 /* Argument is filename pointing to SSH1 private key file */
370 if (i->type!=t_string) {
371 cfgfatal(i->loc,"rsa-private","first argument must be a string\n");
373 filename=i->data.string;
375 filename=NULL; /* Make compiler happy */
376 cfgfatal(loc,"rsa-private","you must provide a filename\n");
379 f=fopen(filename,"rb");
381 if (just_check_config) {
382 Message(M_WARNING,"rsa-private (%s:%d): cannot open keyfile "
383 "\"%s\"; assuming it's valid while we check the "
384 "rest of the configuration\n",loc.file,loc.line,filename);
387 fatal_perror("rsa-private (%s:%d): cannot open file \"%s\"",
388 loc.file,loc.line,filename);
392 /* Check that the ID string is correct */
393 length=strlen(AUTHFILE_ID_STRING)+1;
394 b=safe_malloc(length,"rsapriv_apply");
395 if (fread(b,length,1,f)!=1 || memcmp(b,AUTHFILE_ID_STRING,length)!=0) {
396 cfgfatal_maybefile(f,loc,"rsa-private","failed to read magic ID"
397 " string from SSH1 private keyfile \"%s\"\n",
402 cipher_type=fgetc(f);
403 keyfile_get_int(loc,f); /* "Reserved data" */
404 if (cipher_type != 0) {
405 cfgfatal(loc,"rsa-private","we don't support encrypted keyfiles\n");
408 /* Read the public key */
409 keyfile_get_int(loc,f); /* Not sure what this is */
410 length=(keyfile_get_short(loc,f)+7)/8;
411 if (length>RSA_MAX_MODBYTES) {
412 cfgfatal(loc,"rsa-private","implausible length %ld for modulus\n",
415 b=safe_malloc(length,"rsapriv_apply");
416 if (fread(b,length,1,f) != 1) {
417 cfgfatal_maybefile(f,loc,"rsa-private","error reading modulus\n");
420 read_mpbin(&st->n,b,length);
422 length=(keyfile_get_short(loc,f)+7)/8;
423 if (length>RSA_MAX_MODBYTES) {
424 cfgfatal(loc,"rsa-private","implausible length %ld for e\n",length);
426 b=safe_malloc(length,"rsapriv_apply");
427 if (fread(b,length,1,f)!=1) {
428 cfgfatal_maybefile(f,loc,"rsa-private","error reading e\n");
431 read_mpbin(&e,b,length);
434 length=keyfile_get_int(loc,f);
436 cfgfatal(loc,"rsa-private","implausibly long (%ld) key comment\n",
439 c=safe_malloc(length+1,"rsapriv_apply");
440 if (fread(c,length,1,f)!=1) {
441 cfgfatal_maybefile(f,loc,"rsa-private","error reading key comment\n");
445 /* Check that the next two pairs of characters are identical - the
446 keyfile is not encrypted, so they should be */
448 if (keyfile_get_short(loc,f) != keyfile_get_short(loc,f)) {
449 cfgfatal(loc,"rsa-private","corrupt keyfile\n");
453 length=(keyfile_get_short(loc,f)+7)/8;
454 if (length>RSA_MAX_MODBYTES) {
455 cfgfatal(loc,"rsa-private","implausibly long (%ld) decryption key\n",
458 b=safe_malloc(length,"rsapriv_apply");
459 if (fread(b,length,1,f)!=1) {
460 cfgfatal_maybefile(f,loc,"rsa-private",
461 "error reading decryption key\n");
464 read_mpbin(&d,b,length);
466 /* Read iqmp (inverse of q mod p) */
467 length=(keyfile_get_short(loc,f)+7)/8;
468 if (length>RSA_MAX_MODBYTES) {
469 cfgfatal(loc,"rsa-private","implausibly long (%ld)"
470 " iqmp auxiliary value\n", length);
472 b=safe_malloc(length,"rsapriv_apply");
473 if (fread(b,length,1,f)!=1) {
474 cfgfatal_maybefile(f,loc,"rsa-private",
475 "error reading decryption key\n");
478 read_mpbin(&iqmp,b,length);
480 /* Read q (the smaller of the two primes) */
481 length=(keyfile_get_short(loc,f)+7)/8;
482 if (length>RSA_MAX_MODBYTES) {
483 cfgfatal(loc,"rsa-private","implausibly long (%ld) q value\n",
486 b=safe_malloc(length,"rsapriv_apply");
487 if (fread(b,length,1,f)!=1) {
488 cfgfatal_maybefile(f,loc,"rsa-private",
489 "error reading q value\n");
492 read_mpbin(&st->q,b,length);
494 /* Read p (the larger of the two primes) */
495 length=(keyfile_get_short(loc,f)+7)/8;
496 if (length>RSA_MAX_MODBYTES) {
497 cfgfatal(loc,"rsa-private","implausibly long (%ld) p value\n",
500 b=safe_malloc(length,"rsapriv_apply");
501 if (fread(b,length,1,f)!=1) {
502 cfgfatal_maybefile(f,loc,"rsa-private",
503 "error reading p value\n");
506 read_mpbin(&st->p,b,length);
510 fatal_perror("rsa-private (%s:%d): fclose",loc.file,loc.line);
514 * Now verify the validity of the key, and set up the auxiliary
515 * values for fast CRT signing.
522 if (i && i->type==t_bool && i->data.bool==False) {
523 Message(M_INFO,"rsa-private (%s:%d): skipping RSA key validity "
524 "check\n",loc.file,loc.line);
526 /* Verify that p*q is equal to n. */
527 mpz_mul(&tmp, &st->p, &st->q);
528 if (mpz_cmp(&tmp, &st->n) != 0)
532 * Verify that d*e is congruent to 1 mod (p-1), and mod
533 * (q-1). This is equivalent to it being congruent to 1 mod
534 * lambda(n) = lcm(p-1,q-1). The usual `textbook' condition,
535 * that d e == 1 (mod (p-1)(q-1)) is sufficient, but not
536 * actually necessary.
538 mpz_mul(&tmp, &d, &e);
539 mpz_sub_ui(&tmp2, &st->p, 1);
540 mpz_mod(&tmp3, &tmp, &tmp2);
541 if (mpz_cmp_si(&tmp3, 1) != 0)
543 mpz_sub_ui(&tmp2, &st->q, 1);
544 mpz_mod(&tmp3, &tmp, &tmp2);
545 if (mpz_cmp_si(&tmp3, 1) != 0)
548 /* Verify that q*iqmp is congruent to 1 mod p. */
549 mpz_mul(&tmp, &st->q, &iqmp);
550 mpz_mod(&tmp2, &tmp, &st->p);
551 if (mpz_cmp_si(&tmp2, 1) != 0)
554 /* Now we know the key is valid (or we don't care). */
558 * Now we compute auxiliary values dp, dq and w to allow us
559 * to use the CRT optimisation when signing.
561 * dp == d mod (p-1) so that a^dp == a^d mod p, for all a
562 * dq == d mod (q-1) similarly mod q
563 * w == iqmp * q so that w == 0 mod q, and w == 1 mod p
568 mpz_sub_ui(&tmp, &st->p, 1);
569 mpz_mod(&st->dp, &d, &tmp);
570 mpz_sub_ui(&tmp, &st->q, 1);
571 mpz_mod(&st->dq, &d, &tmp);
572 mpz_mul(&st->w, &iqmp, &st->q);
576 cfgfatal(loc,"rsa-private","file \"%s\" does not contain a "
577 "valid RSA key!\n",filename);
589 return new_closure(&st->cl);
592 void rsa_module(dict_t *dict)
594 add_closure(dict,"rsa-private",rsapriv_apply);
595 add_closure(dict,"rsa-public",rsapub_apply);