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)
46 struct sigprivkey_if ops;
55 struct sigpubkey_if ops;
60 /* Sign data. NB data must be smaller than modulus */
62 #define RSA_MAX_MODBYTES 2048
63 /* The largest modulus I've seen is 15360 bits, which works out at 1920
64 * bytes. Using keys this big is quite implausible, but it doesn't cost us
65 * much to support them.
68 static const char *hexchars="0123456789abcdef";
70 static void emsa_pkcs1(MP_INT *n, MP_INT *m,
71 const uint8_t *data, int32_t datalen)
73 char buff[2*RSA_MAX_MODBYTES + 1];
76 /* RSA PKCS#1 v1.5 signature padding:
78 * <------------ msize hex digits ---------->
80 * 00 01 ff ff .... ff ff 00 vv vv vv .... vv
84 * = datalen*2 hex digits
86 * NB that according to PKCS#1 v1.5 we're supposed to include a
87 * hash function OID in the data. We don't do that (because we
88 * don't have the hash function OID to hand here), thus violating
89 * the spec in a way that affects interop but not security.
94 msize=mpz_sizeinbase(n, 16);
96 if (datalen*2+6>=msize) {
97 fatal("rsa_sign: message too big");
102 for (i=0; i<datalen; i++) {
103 buff[msize+(-datalen+i)*2]=hexchars[(data[i]&0xf0)>>4];
104 buff[msize+(-datalen+i)*2+1]=hexchars[data[i]&0xf];
107 buff[msize-datalen*2-2]= '0';
108 buff[msize-datalen*2-1]= '0';
110 for (i=4; i<msize-datalen*2-2; i++)
115 mpz_set_str(m, buff, 16);
118 static bool_t rsa_sign(void *sst, uint8_t *data, int32_t datalen,
119 struct buffer_if *msg)
121 struct rsapriv *st=sst;
122 MP_INT a, b, u, v, tmp, tmp2;
123 string_t signature = 0;
129 /* Construct the message representative. */
130 emsa_pkcs1(&st->n, &a, data, datalen);
133 * Produce an RSA signature (a^d mod n) using the Chinese
134 * Remainder Theorem. We compute:
136 * u = a^dp mod p (== a^d mod p, since dp == d mod (p-1))
137 * v = a^dq mod q (== a^d mod q, similarly)
139 * We also know w == iqmp * q, which has the property that w ==
140 * 0 mod q and w == 1 mod p. So (1-w) has the reverse property
141 * (congruent to 0 mod p and to 1 mod q). Hence we now compute
143 * b = w * u + (1-w) * v
146 * so that b is congruent to a^d both mod p and mod q. Hence b,
147 * reduced mod n, is the required signature.
154 mpz_powm_sec(&u, &a, &st->dp, &st->p);
155 mpz_powm_sec(&v, &a, &st->dq, &st->q);
156 mpz_sub(&tmp, &u, &v);
157 mpz_mul(&tmp2, &tmp, &st->w);
158 mpz_add(&tmp, &tmp2, &v);
159 mpz_mod(&b, &tmp, &st->n);
166 signature=write_mpstring(&b);
168 uint8_t *op = buf_append(msg,2);
169 if (!op) { ok=False; goto out; }
170 size_t l = strlen(signature);
173 op = buf_append(msg,l);
174 if (!op) { ok=False; goto out; }
175 memcpy(op, signature, l);
186 static bool_t rsa_sig_unpick(void *sst, struct buffer_if *msg,
187 struct alg_msg_data *sig)
189 uint8_t *lp = buf_unprepend(msg, 2);
190 if (!lp) return False;
191 sig->siglen = get_uint16(lp);
192 sig->sigstart = buf_unprepend(msg, sig->siglen);
193 if (!sig->sigstart) return False;
195 /* In `rsa_sig_check' below, we assume that we can write a nul
196 * terminator following the signature. Make sure there's enough space.
198 if (msg->start >= msg->base + msg->alloclen)
204 static sig_checksig_fn rsa_sig_check;
205 static bool_t rsa_sig_check(void *sst, uint8_t *data, int32_t datalen,
206 const struct alg_msg_data *sig)
208 struct rsapub *st=sst;
216 emsa_pkcs1(&st->n, &a, data, datalen);
218 /* Terminate signature with a '0' - already checked that this will fit */
219 int save = sig->sigstart[sig->siglen];
220 sig->sigstart[sig->siglen] = 0;
221 mpz_set_str(&b, sig->sigstart, 16);
222 sig->sigstart[sig->siglen] = save;
224 mpz_powm(&c, &b, &st->e, &st->n);
226 ok=(mpz_cmp(&a, &c)==0);
235 static list_t *rsapub_apply(closure_t *self, struct cloc loc, dict_t *context,
243 st->cl.description="rsapub";
244 st->cl.type=CL_SIGPUBKEY;
246 st->cl.interface=&st->ops;
248 st->ops.unpick=rsa_sig_unpick;
249 st->ops.check=rsa_sig_check;
254 if (i->type!=t_string) {
255 cfgfatal(i->loc,"rsa-public","first argument must be a string\n");
258 if (mpz_init_set_str(&st->e,e,10)!=0) {
259 cfgfatal(i->loc,"rsa-public","encryption key \"%s\" is not a "
260 "decimal number string\n",e);
263 cfgfatal(loc,"rsa-public","you must provide an encryption key\n");
265 if (mpz_sizeinbase(&st->e, 256) > RSA_MAX_MODBYTES) {
266 cfgfatal(loc, "rsa-public", "implausibly large public exponent\n");
271 if (i->type!=t_string) {
272 cfgfatal(i->loc,"rsa-public","second argument must be a string\n");
275 if (mpz_init_set_str(&st->n,n,10)!=0) {
276 cfgfatal(i->loc,"rsa-public","modulus \"%s\" is not a decimal "
277 "number string\n",n);
280 cfgfatal(loc,"rsa-public","you must provide a modulus\n");
282 if (mpz_sizeinbase(&st->n, 256) > RSA_MAX_MODBYTES) {
283 cfgfatal(loc, "rsa-public", "implausibly large modulus\n");
285 return new_closure(&st->cl);
288 static uint32_t keyfile_get_int(struct cloc loc, FILE *f)
295 cfgfile_postreadcheck(loc,f);
299 static uint16_t keyfile_get_short(struct cloc loc, FILE *f)
304 cfgfile_postreadcheck(loc,f);
308 static list_t *rsapriv_apply(closure_t *self, struct cloc loc, dict_t *context,
318 MP_INT e,d,iqmp,tmp,tmp2,tmp3;
322 st->cl.description="rsapriv";
323 st->cl.type=CL_SIGPRIVKEY;
325 st->cl.interface=&st->ops;
327 st->ops.sign=rsa_sign;
330 /* Argument is filename pointing to SSH1 private key file */
333 if (i->type!=t_string) {
334 cfgfatal(i->loc,"rsa-private","first argument must be a string\n");
336 filename=i->data.string;
338 filename=NULL; /* Make compiler happy */
339 cfgfatal(loc,"rsa-private","you must provide a filename\n");
342 f=fopen(filename,"rb");
344 if (just_check_config) {
345 Message(M_WARNING,"rsa-private (%s:%d): cannot open keyfile "
346 "\"%s\"; assuming it's valid while we check the "
347 "rest of the configuration\n",loc.file,loc.line,filename);
350 fatal_perror("rsa-private (%s:%d): cannot open file \"%s\"",
351 loc.file,loc.line,filename);
355 /* Check that the ID string is correct */
356 length=strlen(AUTHFILE_ID_STRING)+1;
357 b=safe_malloc(length,"rsapriv_apply");
358 if (fread(b,length,1,f)!=1 || memcmp(b,AUTHFILE_ID_STRING,length)!=0) {
359 cfgfatal_maybefile(f,loc,"rsa-private","failed to read magic ID"
360 " string from SSH1 private keyfile \"%s\"\n",
365 cipher_type=fgetc(f);
366 keyfile_get_int(loc,f); /* "Reserved data" */
367 if (cipher_type != 0) {
368 cfgfatal(loc,"rsa-private","we don't support encrypted keyfiles\n");
371 /* Read the public key */
372 keyfile_get_int(loc,f); /* Not sure what this is */
373 length=(keyfile_get_short(loc,f)+7)/8;
374 if (length>RSA_MAX_MODBYTES) {
375 cfgfatal(loc,"rsa-private","implausible length %ld for modulus\n",
378 b=safe_malloc(length,"rsapriv_apply");
379 if (fread(b,length,1,f) != 1) {
380 cfgfatal_maybefile(f,loc,"rsa-private","error reading modulus\n");
383 read_mpbin(&st->n,b,length);
385 length=(keyfile_get_short(loc,f)+7)/8;
386 if (length>RSA_MAX_MODBYTES) {
387 cfgfatal(loc,"rsa-private","implausible length %ld for e\n",length);
389 b=safe_malloc(length,"rsapriv_apply");
390 if (fread(b,length,1,f)!=1) {
391 cfgfatal_maybefile(f,loc,"rsa-private","error reading e\n");
394 read_mpbin(&e,b,length);
397 length=keyfile_get_int(loc,f);
399 cfgfatal(loc,"rsa-private","implausibly long (%ld) key comment\n",
402 c=safe_malloc(length+1,"rsapriv_apply");
403 if (fread(c,length,1,f)!=1) {
404 cfgfatal_maybefile(f,loc,"rsa-private","error reading key comment\n");
408 /* Check that the next two pairs of characters are identical - the
409 keyfile is not encrypted, so they should be */
411 if (keyfile_get_short(loc,f) != keyfile_get_short(loc,f)) {
412 cfgfatal(loc,"rsa-private","corrupt keyfile\n");
416 length=(keyfile_get_short(loc,f)+7)/8;
417 if (length>RSA_MAX_MODBYTES) {
418 cfgfatal(loc,"rsa-private","implausibly long (%ld) decryption key\n",
421 b=safe_malloc(length,"rsapriv_apply");
422 if (fread(b,length,1,f)!=1) {
423 cfgfatal_maybefile(f,loc,"rsa-private",
424 "error reading decryption key\n");
427 read_mpbin(&d,b,length);
429 /* Read iqmp (inverse of q mod p) */
430 length=(keyfile_get_short(loc,f)+7)/8;
431 if (length>RSA_MAX_MODBYTES) {
432 cfgfatal(loc,"rsa-private","implausibly long (%ld)"
433 " iqmp auxiliary value\n", length);
435 b=safe_malloc(length,"rsapriv_apply");
436 if (fread(b,length,1,f)!=1) {
437 cfgfatal_maybefile(f,loc,"rsa-private",
438 "error reading decryption key\n");
441 read_mpbin(&iqmp,b,length);
443 /* Read q (the smaller of the two primes) */
444 length=(keyfile_get_short(loc,f)+7)/8;
445 if (length>RSA_MAX_MODBYTES) {
446 cfgfatal(loc,"rsa-private","implausibly long (%ld) q value\n",
449 b=safe_malloc(length,"rsapriv_apply");
450 if (fread(b,length,1,f)!=1) {
451 cfgfatal_maybefile(f,loc,"rsa-private",
452 "error reading q value\n");
455 read_mpbin(&st->q,b,length);
457 /* Read p (the larger of the two primes) */
458 length=(keyfile_get_short(loc,f)+7)/8;
459 if (length>RSA_MAX_MODBYTES) {
460 cfgfatal(loc,"rsa-private","implausibly long (%ld) p value\n",
463 b=safe_malloc(length,"rsapriv_apply");
464 if (fread(b,length,1,f)!=1) {
465 cfgfatal_maybefile(f,loc,"rsa-private",
466 "error reading p value\n");
469 read_mpbin(&st->p,b,length);
473 fatal_perror("rsa-private (%s:%d): fclose",loc.file,loc.line);
477 * Now verify the validity of the key, and set up the auxiliary
478 * values for fast CRT signing.
485 if (i && i->type==t_bool && i->data.bool==False) {
486 Message(M_INFO,"rsa-private (%s:%d): skipping RSA key validity "
487 "check\n",loc.file,loc.line);
489 /* Verify that p*q is equal to n. */
490 mpz_mul(&tmp, &st->p, &st->q);
491 if (mpz_cmp(&tmp, &st->n) != 0)
495 * Verify that d*e is congruent to 1 mod (p-1), and mod
496 * (q-1). This is equivalent to it being congruent to 1 mod
497 * lambda(n) = lcm(p-1,q-1). The usual `textbook' condition,
498 * that d e == 1 (mod (p-1)(q-1)) is sufficient, but not
499 * actually necessary.
501 mpz_mul(&tmp, &d, &e);
502 mpz_sub_ui(&tmp2, &st->p, 1);
503 mpz_mod(&tmp3, &tmp, &tmp2);
504 if (mpz_cmp_si(&tmp3, 1) != 0)
506 mpz_sub_ui(&tmp2, &st->q, 1);
507 mpz_mod(&tmp3, &tmp, &tmp2);
508 if (mpz_cmp_si(&tmp3, 1) != 0)
511 /* Verify that q*iqmp is congruent to 1 mod p. */
512 mpz_mul(&tmp, &st->q, &iqmp);
513 mpz_mod(&tmp2, &tmp, &st->p);
514 if (mpz_cmp_si(&tmp2, 1) != 0)
517 /* Now we know the key is valid (or we don't care). */
521 * Now we compute auxiliary values dp, dq and w to allow us
522 * to use the CRT optimisation when signing.
524 * dp == d mod (p-1) so that a^dp == a^d mod p, for all a
525 * dq == d mod (q-1) similarly mod q
526 * w == iqmp * q so that w == 0 mod q, and w == 1 mod p
531 mpz_sub_ui(&tmp, &st->p, 1);
532 mpz_mod(&st->dp, &d, &tmp);
533 mpz_sub_ui(&tmp, &st->q, 1);
534 mpz_mod(&st->dq, &d, &tmp);
535 mpz_mul(&st->w, &iqmp, &st->q);
539 cfgfatal(loc,"rsa-private","file \"%s\" does not contain a "
540 "valid RSA key!\n",filename);
552 return new_closure(&st->cl);
555 void rsa_module(dict_t *dict)
557 add_closure(dict,"rsa-private",rsapriv_apply);
558 add_closure(dict,"rsa-public",rsapub_apply);