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);
93 static void rsacommon_dispose(struct rsacommon *c)
98 static void emsa_pkcs1(MP_INT *n, MP_INT *m,
99 const uint8_t *data, int32_t datalen)
101 char buff[2*RSA_MAX_MODBYTES + 1];
104 /* RSA PKCS#1 v1.5 signature padding:
106 * <------------ msize hex digits ---------->
108 * 00 01 ff ff .... ff ff 00 vv vv vv .... vv
112 * = datalen*2 hex digits
114 * NB that according to PKCS#1 v1.5 we're supposed to include a
115 * hash function OID in the data. We don't do that (because we
116 * don't have the hash function OID to hand here), thus violating
117 * the spec in a way that affects interop but not security.
122 msize=mpz_sizeinbase(n, 16);
124 if (datalen*2+6>=msize) {
125 fatal("rsa: message too big");
130 for (i=0; i<datalen; i++) {
131 buff[msize+(-datalen+i)*2]=hexchars[(data[i]&0xf0)>>4];
132 buff[msize+(-datalen+i)*2+1]=hexchars[data[i]&0xf];
135 buff[msize-datalen*2-2]= '0';
136 buff[msize-datalen*2-1]= '0';
138 for (i=4; i<msize-datalen*2-2; i++)
143 mpz_set_str(m, buff, 16);
146 static bool_t rsa_sign(void *sst, uint8_t *data, int32_t datalen,
147 struct buffer_if *msg)
149 struct rsapriv *st=sst;
150 MP_INT a, b, u, v, tmp, tmp2;
151 string_t signature = 0;
157 hash_hash(st->ops.hash,data,datalen,st->common.hashbuf);
158 /* Construct the message representative. */
159 emsa_pkcs1(&st->n, &a, st->common.hashbuf, st->ops.hash->hlen);
162 * Produce an RSA signature (a^d mod n) using the Chinese
163 * Remainder Theorem. We compute:
165 * u = a^dp mod p (== a^d mod p, since dp == d mod (p-1))
166 * v = a^dq mod q (== a^d mod q, similarly)
168 * We also know w == iqmp * q, which has the property that w ==
169 * 0 mod q and w == 1 mod p. So (1-w) has the reverse property
170 * (congruent to 0 mod p and to 1 mod q). Hence we now compute
172 * b = w * u + (1-w) * v
175 * so that b is congruent to a^d both mod p and mod q. Hence b,
176 * reduced mod n, is the required signature.
183 mpz_powm_sec(&u, &a, &st->dp, &st->p);
184 mpz_powm_sec(&v, &a, &st->dq, &st->q);
185 mpz_sub(&tmp, &u, &v);
186 mpz_mul(&tmp2, &tmp, &st->w);
187 mpz_add(&tmp, &tmp2, &v);
188 mpz_mod(&b, &tmp, &st->n);
195 signature=write_mpstring(&b);
197 uint8_t *op = buf_append(msg,2);
198 if (!op) { ok=False; goto out; }
199 size_t l = strlen(signature);
202 op = buf_append(msg,l);
203 if (!op) { ok=False; goto out; }
204 memcpy(op, signature, l);
215 static bool_t rsa_sig_unpick(void *sst, struct buffer_if *msg,
216 struct alg_msg_data *sig)
218 uint8_t *lp = buf_unprepend(msg, 2);
219 if (!lp) return False;
220 sig->len = get_uint16(lp);
221 sig->start = buf_unprepend(msg, sig->len);
222 if (!sig->start) return False;
224 /* In `rsa_sig_check' below, we assume that we can write a nul
225 * terminator following the signature. Make sure there's enough space.
227 if (msg->start >= msg->base + msg->alloclen)
233 static sig_checksig_fn rsa_sig_check;
234 static bool_t rsa_sig_check(void *sst, uint8_t *data, int32_t datalen,
235 const struct alg_msg_data *sig)
237 struct rsapub *st=sst;
245 hash_hash(st->ops.hash,data,datalen,st->common.hashbuf);
246 emsa_pkcs1(&st->n, &a, st->common.hashbuf, st->ops.hash->hlen);
248 /* Terminate signature with a '0' - already checked that this will fit */
249 int save = sig->start[sig->len];
250 sig->start[sig->len] = 0;
251 mpz_set_str(&b, sig->start, 16);
252 sig->start[sig->len] = save;
254 mpz_powm(&c, &b, &st->e, &st->n);
256 ok=(mpz_cmp(&a, &c)==0);
265 static void rsapub_dispose(void *sst) {
266 struct rsapub *st=sst;
270 rsacommon_dispose(&st->common);
274 static list_t *rsapub_apply(closure_t *self, struct cloc loc, dict_t *context,
282 st->cl.description="rsapub";
283 st->cl.type=CL_SIGPUBKEY;
285 st->cl.interface=&st->ops;
287 st->ops.sethash=rsa_pub_sethash;
288 st->common.hashbuf=NULL;
289 st->ops.unpick=rsa_sig_unpick;
290 st->ops.check=rsa_sig_check;
292 st->ops.dispose=rsapub_dispose;
297 if (i->type!=t_string) {
298 cfgfatal(i->loc,"rsa-public","first argument must be a string\n");
301 if (mpz_init_set_str(&st->e,e,10)!=0) {
302 cfgfatal(i->loc,"rsa-public","encryption key \"%s\" is not a "
303 "decimal number string\n",e);
306 cfgfatal(loc,"rsa-public","you must provide an encryption key\n");
308 if (mpz_sizeinbase(&st->e, 256) > RSA_MAX_MODBYTES) {
309 cfgfatal(loc, "rsa-public", "implausibly large public exponent\n");
314 if (i->type!=t_string) {
315 cfgfatal(i->loc,"rsa-public","second argument must be a string\n");
318 if (mpz_init_set_str(&st->n,n,10)!=0) {
319 cfgfatal(i->loc,"rsa-public","modulus \"%s\" is not a decimal "
320 "number string\n",n);
323 cfgfatal(loc,"rsa-public","you must provide a modulus\n");
325 if (mpz_sizeinbase(&st->n, 256) > RSA_MAX_MODBYTES) {
326 cfgfatal(loc, "rsa-public", "implausibly large modulus\n");
328 return new_closure(&st->cl);
331 static uint32_t keyfile_get_int(struct cloc loc, FILE *f)
338 cfgfile_postreadcheck(loc,f);
342 static uint16_t keyfile_get_short(struct cloc loc, FILE *f)
347 cfgfile_postreadcheck(loc,f);
351 #define LDFATAL(...) cfgfatal(loc,"rsa-private",__VA_ARGS__)
352 #define LDUNSUP(...) cfgfatal(loc,"rsa-private",__VA_ARGS__)
353 #define LDFATAL_FILE(...) cfgfatal_maybefile(f,loc,"rsa-private",__VA_ARGS__)
354 #define LDUNSUP_FILE(...) cfgfatal_maybefile(f,loc,"rsa-private",__VA_ARGS__)
355 #define FREE(b) free(b)
357 static void rsapriv_dispose(void *sst)
359 struct rsapriv *st=sst;
361 mpz_clear(&st->p); mpz_clear(&st->dp);
362 mpz_clear(&st->q); mpz_clear(&st->dq);
364 rsacommon_dispose(&st->common);
368 static struct rsapriv *rsa_loadpriv_core(FILE *f, struct cloc loc,
369 bool_t do_validity_check,
370 const char *filename)
372 struct rsapriv *st=0;
376 MP_INT e,d,iqmp,tmp,tmp2,tmp3;
387 st->cl.description="rsapriv";
388 st->cl.type=CL_SIGPRIVKEY;
390 st->cl.interface=&st->ops;
392 st->ops.sethash=rsa_priv_sethash;
393 st->common.hashbuf=NULL;
394 st->ops.sign=rsa_sign;
396 st->ops.dispose=rsapriv_dispose;
406 assert(just_check_config);
410 /* Check that the ID string is correct */
411 length=strlen(AUTHFILE_ID_STRING)+1;
412 b=safe_malloc(length,"rsapriv_apply");
413 if (fread(b,length,1,f)!=1 || memcmp(b,AUTHFILE_ID_STRING,length)!=0) {
414 LDUNSUP_FILE("failed to read magic ID"
415 " string from SSH1 private keyfile \"%s\"\n",
420 cipher_type=fgetc(f);
421 keyfile_get_int(loc,f); /* "Reserved data" */
422 if (cipher_type != 0) {
423 LDUNSUP("we don't support encrypted keyfiles\n");
426 /* Read the public key */
427 keyfile_get_int(loc,f); /* Not sure what this is */
428 length=(keyfile_get_short(loc,f)+7)/8;
429 if (length>RSA_MAX_MODBYTES) {
430 LDFATAL("implausible length %ld for modulus\n",
433 b=safe_malloc(length,"rsapriv_apply");
434 if (fread(b,length,1,f) != 1) {
435 LDFATAL_FILE("error reading modulus\n");
437 read_mpbin(&st->n,b,length);
439 length=(keyfile_get_short(loc,f)+7)/8;
440 if (length>RSA_MAX_MODBYTES) {
441 LDFATAL("implausible length %ld for e\n",length);
443 b=safe_malloc(length,"rsapriv_apply");
444 if (fread(b,length,1,f)!=1) {
445 LDFATAL_FILE("error reading e\n");
447 read_mpbin(&e,b,length);
450 length=keyfile_get_int(loc,f);
452 LDFATAL("implausibly long (%ld) key comment\n",
455 c=safe_malloc(length+1,"rsapriv_apply");
456 if (fread(c,length,1,f)!=1) {
457 LDFATAL_FILE("error reading key comment\n");
461 /* Check that the next two pairs of characters are identical - the
462 keyfile is not encrypted, so they should be */
464 if (keyfile_get_short(loc,f) != keyfile_get_short(loc,f)) {
465 LDFATAL("corrupt keyfile\n");
469 length=(keyfile_get_short(loc,f)+7)/8;
470 if (length>RSA_MAX_MODBYTES) {
471 LDFATAL("implausibly long (%ld) decryption key\n",
474 b=safe_malloc(length,"rsapriv_apply");
475 if (fread(b,length,1,f)!=1) {
476 LDFATAL_FILE("error reading decryption key\n");
478 read_mpbin(&d,b,length);
480 /* Read iqmp (inverse of q mod p) */
481 length=(keyfile_get_short(loc,f)+7)/8;
482 if (length>RSA_MAX_MODBYTES) {
483 LDFATAL("implausibly long (%ld)"
484 " iqmp auxiliary value\n", length);
486 b=safe_malloc(length,"rsapriv_apply");
487 if (fread(b,length,1,f)!=1) {
488 LDFATAL_FILE("error reading decryption key\n");
490 read_mpbin(&iqmp,b,length);
492 /* Read q (the smaller of the two primes) */
493 length=(keyfile_get_short(loc,f)+7)/8;
494 if (length>RSA_MAX_MODBYTES) {
495 LDFATAL("implausibly long (%ld) q value\n",
498 b=safe_malloc(length,"rsapriv_apply");
499 if (fread(b,length,1,f)!=1) {
500 LDFATAL_FILE("error reading q value\n");
502 read_mpbin(&st->q,b,length);
504 /* Read p (the larger of the two primes) */
505 length=(keyfile_get_short(loc,f)+7)/8;
506 if (length>RSA_MAX_MODBYTES) {
507 LDFATAL("implausibly long (%ld) p value\n",
510 b=safe_malloc(length,"rsapriv_apply");
511 if (fread(b,length,1,f)!=1) {
512 LDFATAL_FILE("error reading p value\n");
514 read_mpbin(&st->p,b,length);
518 fatal_perror("rsa-private (%s:%d): ferror",loc.file,loc.line);
522 * Now verify the validity of the key, and set up the auxiliary
523 * values for fast CRT signing.
526 if (do_validity_check) {
527 /* Verify that p*q is equal to n. */
528 mpz_mul(&tmp, &st->p, &st->q);
529 if (mpz_cmp(&tmp, &st->n) != 0)
533 * Verify that d*e is congruent to 1 mod (p-1), and mod
534 * (q-1). This is equivalent to it being congruent to 1 mod
535 * lambda(n) = lcm(p-1,q-1). The usual `textbook' condition,
536 * that d e == 1 (mod (p-1)(q-1)) is sufficient, but not
537 * actually necessary.
539 mpz_mul(&tmp, &d, &e);
540 mpz_sub_ui(&tmp2, &st->p, 1);
541 mpz_mod(&tmp3, &tmp, &tmp2);
542 if (mpz_cmp_si(&tmp3, 1) != 0)
544 mpz_sub_ui(&tmp2, &st->q, 1);
545 mpz_mod(&tmp3, &tmp, &tmp2);
546 if (mpz_cmp_si(&tmp3, 1) != 0)
549 /* Verify that q*iqmp is congruent to 1 mod p. */
550 mpz_mul(&tmp, &st->q, &iqmp);
551 mpz_mod(&tmp2, &tmp, &st->p);
552 if (mpz_cmp_si(&tmp2, 1) != 0)
555 /* Now we know the key is valid (or we don't care). */
559 * Now we compute auxiliary values dp, dq and w to allow us
560 * to use the CRT optimisation when signing.
562 * dp == d mod (p-1) so that a^dp == a^d mod p, for all a
563 * dq == d mod (q-1) similarly mod q
564 * w == iqmp * q so that w == 0 mod q, and w == 1 mod p
566 mpz_sub_ui(&tmp, &st->p, 1);
567 mpz_mod(&st->dp, &d, &tmp);
568 mpz_sub_ui(&tmp, &st->q, 1);
569 mpz_mod(&st->dq, &d, &tmp);
570 mpz_mul(&st->w, &iqmp, &st->q);
574 LDFATAL("file \"%s\" does not contain a "
575 "valid RSA key!\n",filename);
591 static list_t *rsapriv_apply(closure_t *self, struct cloc loc, dict_t *context,
599 /* Argument is filename pointing to SSH1 private key file */
602 if (i->type!=t_string) {
603 cfgfatal(i->loc,"rsa-private","first argument must be a string\n");
605 filename=i->data.string;
607 filename=NULL; /* Make compiler happy */
608 cfgfatal(i->loc,"rsa-private","you must provide a filename\n");
611 f=fopen(filename,"rb");
613 if (just_check_config) {
614 Message(M_WARNING,"rsa-private (%s:%d): cannot open keyfile "
615 "\"%s\"; assuming it's valid while we check the "
616 "rest of the configuration\n",loc.file,loc.line,filename);
618 fatal_perror("rsa-private (%s:%d): cannot open file \"%s\"",
619 loc.file,loc.line,filename);
623 bool_t do_validity_check=True;
625 if (i && i->type==t_bool && i->data.bool==False) {
626 Message(M_INFO,"rsa-private (%s:%d): skipping RSA key validity "
627 "check\n",loc.file,loc.line);
628 do_validity_check=False;
631 st=rsa_loadpriv_core(f,loc,do_validity_check,filename);
633 return new_closure(&st->cl);
636 void rsa_module(dict_t *dict)
638 add_closure(dict,"rsa-private",rsapriv_apply);
639 add_closure(dict,"rsa-public",rsapub_apply);