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)
49 void (*verror)(struct load_ctx *l,
50 FILE *maybe_f, bool_t unsup,
51 const char *message, va_list args);
52 bool_t (*postreadcheck)(struct load_ctx *l, FILE *f);
62 static void verror_tryload(struct load_ctx *l,
63 FILE *maybe_f, bool_t unsup,
64 const char *message, va_list args)
66 int class=unsup ? M_DEBUG : M_ERR;
67 slilog_part(l->u.tryload.log,class,"rsa1priv load: ");
68 vslilog(l->u.tryload.log,class,message,args);
71 static void verror_cfgfatal(struct load_ctx *l,
72 FILE *maybe_f, bool_t unsup,
73 const char *message, va_list args)
75 vcfgfatal_maybefile(maybe_f,*l->loc,"rsa-private",message,args);
80 struct sigprivkey_if ops;
82 struct rsacommon common;
90 struct sigpubkey_if ops;
92 struct rsacommon common;
96 /* Sign data. NB data must be smaller than modulus */
98 #define RSA_MAX_MODBYTES 2048
99 /* The largest modulus I've seen is 15360 bits, which works out at 1920
100 * bytes. Using keys this big is quite implausible, but it doesn't cost us
101 * much to support them.
104 static const char *hexchars="0123456789abcdef";
106 static void rsa_sethash(struct rsacommon *c, struct hash_if *hash,
107 const struct hash_if **in_ops)
110 c->hashbuf=safe_malloc(hash->hlen, "generate_msg");
113 static void rsa_pub_sethash(void *sst, struct hash_if *hash)
115 struct rsapub *st=sst;
116 rsa_sethash(&st->common, hash, &st->ops.hash);
118 static void rsa_priv_sethash(void *sst, struct hash_if *hash)
120 struct rsapriv *st=sst;
121 rsa_sethash(&st->common, hash, &st->ops.hash);
123 static void rsacommon_dispose(struct rsacommon *c)
128 static void emsa_pkcs1(MP_INT *n, MP_INT *m,
129 const uint8_t *data, int32_t datalen)
131 char buff[2*RSA_MAX_MODBYTES + 1];
134 /* RSA PKCS#1 v1.5 signature padding:
136 * <------------ msize hex digits ---------->
138 * 00 01 ff ff .... ff ff 00 vv vv vv .... vv
142 * = datalen*2 hex digits
144 * NB that according to PKCS#1 v1.5 we're supposed to include a
145 * hash function OID in the data. We don't do that (because we
146 * don't have the hash function OID to hand here), thus violating
147 * the spec in a way that affects interop but not security.
152 msize=mpz_sizeinbase(n, 16);
154 if (datalen*2+6>=msize) {
155 fatal("rsa: message too big");
160 for (i=0; i<datalen; i++) {
161 buff[msize+(-datalen+i)*2]=hexchars[(data[i]&0xf0)>>4];
162 buff[msize+(-datalen+i)*2+1]=hexchars[data[i]&0xf];
165 buff[msize-datalen*2-2]= '0';
166 buff[msize-datalen*2-1]= '0';
168 for (i=4; i<msize-datalen*2-2; i++)
173 mpz_set_str(m, buff, 16);
176 static bool_t rsa_sign(void *sst, uint8_t *data, int32_t datalen,
177 struct buffer_if *msg)
179 struct rsapriv *st=sst;
180 MP_INT a, b, u, v, tmp, tmp2;
181 string_t signature = 0;
187 hash_hash(st->ops.hash,data,datalen,st->common.hashbuf);
188 /* Construct the message representative. */
189 emsa_pkcs1(&st->n, &a, st->common.hashbuf, st->ops.hash->hlen);
192 * Produce an RSA signature (a^d mod n) using the Chinese
193 * Remainder Theorem. We compute:
195 * u = a^dp mod p (== a^d mod p, since dp == d mod (p-1))
196 * v = a^dq mod q (== a^d mod q, similarly)
198 * We also know w == iqmp * q, which has the property that w ==
199 * 0 mod q and w == 1 mod p. So (1-w) has the reverse property
200 * (congruent to 0 mod p and to 1 mod q). Hence we now compute
202 * b = w * u + (1-w) * v
205 * so that b is congruent to a^d both mod p and mod q. Hence b,
206 * reduced mod n, is the required signature.
213 mpz_powm_sec(&u, &a, &st->dp, &st->p);
214 mpz_powm_sec(&v, &a, &st->dq, &st->q);
215 mpz_sub(&tmp, &u, &v);
216 mpz_mul(&tmp2, &tmp, &st->w);
217 mpz_add(&tmp, &tmp2, &v);
218 mpz_mod(&b, &tmp, &st->n);
225 signature=write_mpstring(&b);
227 uint8_t *op = buf_append(msg,2);
228 if (!op) { ok=False; goto out; }
229 size_t l = strlen(signature);
232 op = buf_append(msg,l);
233 if (!op) { ok=False; goto out; }
234 memcpy(op, signature, l);
245 static bool_t rsa_sig_unpick(void *sst, struct buffer_if *msg,
246 struct alg_msg_data *sig)
248 uint8_t *lp = buf_unprepend(msg, 2);
249 if (!lp) return False;
250 sig->len = get_uint16(lp);
251 sig->start = buf_unprepend(msg, sig->len);
252 if (!sig->start) return False;
254 /* In `rsa_sig_check' below, we assume that we can write a nul
255 * terminator following the signature. Make sure there's enough space.
257 if (msg->start >= msg->base + msg->alloclen)
263 static sig_checksig_fn rsa_sig_check;
264 static bool_t rsa_sig_check(void *sst, uint8_t *data, int32_t datalen,
265 const struct alg_msg_data *sig)
267 struct rsapub *st=sst;
275 hash_hash(st->ops.hash,data,datalen,st->common.hashbuf);
276 emsa_pkcs1(&st->n, &a, st->common.hashbuf, st->ops.hash->hlen);
278 /* Terminate signature with a '0' - already checked that this will fit */
279 int save = sig->start[sig->len];
280 sig->start[sig->len] = 0;
281 mpz_set_str(&b, sig->start, 16);
282 sig->start[sig->len] = save;
284 mpz_powm(&c, &b, &st->e, &st->n);
286 ok=(mpz_cmp(&a, &c)==0);
295 static void rsapub_dispose(void *sst) {
296 struct rsapub *st=sst;
300 rsacommon_dispose(&st->common);
304 static list_t *rsapub_apply(closure_t *self, struct cloc loc, dict_t *context,
312 st->cl.description="rsapub";
313 st->cl.type=CL_SIGPUBKEY;
315 st->cl.interface=&st->ops;
317 st->ops.sethash=rsa_pub_sethash;
318 st->common.hashbuf=NULL;
319 st->ops.unpick=rsa_sig_unpick;
320 st->ops.check=rsa_sig_check;
322 st->ops.dispose=rsapub_dispose;
327 if (i->type!=t_string) {
328 cfgfatal(i->loc,"rsa-public","first argument must be a string\n");
331 if (mpz_init_set_str(&st->e,e,10)!=0) {
332 cfgfatal(i->loc,"rsa-public","encryption key \"%s\" is not a "
333 "decimal number string\n",e);
336 cfgfatal(loc,"rsa-public","you must provide an encryption key\n");
338 if (mpz_sizeinbase(&st->e, 256) > RSA_MAX_MODBYTES) {
339 cfgfatal(loc, "rsa-public", "implausibly large public exponent\n");
344 if (i->type!=t_string) {
345 cfgfatal(i->loc,"rsa-public","second argument must be a string\n");
348 if (mpz_init_set_str(&st->n,n,10)!=0) {
349 cfgfatal(i->loc,"rsa-public","modulus \"%s\" is not a decimal "
350 "number string\n",n);
353 cfgfatal(loc,"rsa-public","you must provide a modulus\n");
355 if (mpz_sizeinbase(&st->n, 256) > RSA_MAX_MODBYTES) {
356 cfgfatal(loc, "rsa-public", "implausibly large modulus\n");
358 return new_closure(&st->cl);
361 static void load_error(struct load_ctx *l, FILE *maybe_f,
362 bool_t unsup, const char *fmt, ...)
366 l->verror(l,maybe_f,unsup,fmt,al);
370 #define LDFATAL(...) ({ load_error(l,0,0,__VA_ARGS__); goto error_out; })
371 #define LDUNSUP(...) ({ load_error(l,0,1,__VA_ARGS__); goto error_out; })
372 #define LDFATAL_FILE(...) ({ load_error(l,f,0,__VA_ARGS__); goto error_out; })
373 #define LDUNSUP_FILE(...) ({ load_error(l,f,1,__VA_ARGS__); goto error_out; })
374 #define FREE(b) ({ free((b)); (b)=0; })
375 #define KEYFILE_GET(is) ({ \
376 uint##is##_t keyfile_get_tmp=keyfile_get_##is(l,f); \
377 if (!l->postreadcheck(l,f)) goto error_out; \
381 static uint32_t keyfile_get_32(struct load_ctx *l, FILE *f)
391 static uint16_t keyfile_get_16(struct load_ctx *l, FILE *f)
399 static void rsapriv_dispose(void *sst)
401 struct rsapriv *st=sst;
403 mpz_clear(&st->p); mpz_clear(&st->dp);
404 mpz_clear(&st->q); mpz_clear(&st->dq);
406 rsacommon_dispose(&st->common);
410 static struct rsapriv *rsa_loadpriv_core(struct load_ctx *l,
411 FILE *f, struct cloc loc,
412 bool_t do_validity_check)
414 struct rsapriv *st=0;
418 MP_INT e,d,iqmp,tmp,tmp2,tmp3;
429 st->cl.description="rsapriv";
430 st->cl.type=CL_SIGPRIVKEY;
432 st->cl.interface=&st->ops;
434 st->ops.sethash=rsa_priv_sethash;
435 st->common.hashbuf=NULL;
436 st->ops.sign=rsa_sign;
438 st->ops.dispose=rsapriv_dispose;
448 assert(just_check_config);
452 /* Check that the ID string is correct */
453 length=strlen(AUTHFILE_ID_STRING)+1;
454 b=safe_malloc(length,"rsapriv_apply");
455 if (fread(b,length,1,f)!=1 || memcmp(b,AUTHFILE_ID_STRING,length)!=0) {
456 LDUNSUP_FILE("failed to read magic ID"
457 " string from SSH1 private keyfile\n");
461 cipher_type=fgetc(f);
462 KEYFILE_GET(32); /* "Reserved data" */
463 if (cipher_type != 0) {
464 LDUNSUP("we don't support encrypted keyfiles\n");
467 /* Read the public key */
468 KEYFILE_GET(32); /* Not sure what this is */
469 length=(KEYFILE_GET(16)+7)/8;
470 if (length>RSA_MAX_MODBYTES) {
471 LDFATAL("implausible length %ld for modulus\n",
474 b=safe_malloc(length,"rsapriv_apply");
475 if (fread(b,length,1,f) != 1) {
476 LDFATAL_FILE("error reading modulus\n");
478 read_mpbin(&st->n,b,length);
480 length=(KEYFILE_GET(16)+7)/8;
481 if (length>RSA_MAX_MODBYTES) {
482 LDFATAL("implausible length %ld for e\n",length);
484 b=safe_malloc(length,"rsapriv_apply");
485 if (fread(b,length,1,f)!=1) {
486 LDFATAL_FILE("error reading e\n");
488 read_mpbin(&e,b,length);
491 length=KEYFILE_GET(32);
493 LDFATAL("implausibly long (%ld) key comment\n",
496 c=safe_malloc(length+1,"rsapriv_apply");
497 if (fread(c,length,1,f)!=1) {
498 LDFATAL_FILE("error reading key comment\n");
502 /* Check that the next two pairs of characters are identical - the
503 keyfile is not encrypted, so they should be */
505 if (KEYFILE_GET(16) != KEYFILE_GET(16)) {
506 LDFATAL("corrupt keyfile\n");
510 length=(KEYFILE_GET(16)+7)/8;
511 if (length>RSA_MAX_MODBYTES) {
512 LDFATAL("implausibly long (%ld) decryption key\n",
515 b=safe_malloc(length,"rsapriv_apply");
516 if (fread(b,length,1,f)!=1) {
517 LDFATAL_FILE("error reading decryption key\n");
519 read_mpbin(&d,b,length);
521 /* Read iqmp (inverse of q mod p) */
522 length=(KEYFILE_GET(16)+7)/8;
523 if (length>RSA_MAX_MODBYTES) {
524 LDFATAL("implausibly long (%ld)"
525 " iqmp auxiliary value\n", length);
527 b=safe_malloc(length,"rsapriv_apply");
528 if (fread(b,length,1,f)!=1) {
529 LDFATAL_FILE("error reading decryption key\n");
531 read_mpbin(&iqmp,b,length);
533 /* Read q (the smaller of the two primes) */
534 length=(KEYFILE_GET(16)+7)/8;
535 if (length>RSA_MAX_MODBYTES) {
536 LDFATAL("implausibly long (%ld) q value\n",
539 b=safe_malloc(length,"rsapriv_apply");
540 if (fread(b,length,1,f)!=1) {
541 LDFATAL_FILE("error reading q value\n");
543 read_mpbin(&st->q,b,length);
545 /* Read p (the larger of the two primes) */
546 length=(KEYFILE_GET(16)+7)/8;
547 if (length>RSA_MAX_MODBYTES) {
548 LDFATAL("implausibly long (%ld) p value\n",
551 b=safe_malloc(length,"rsapriv_apply");
552 if (fread(b,length,1,f)!=1) {
553 LDFATAL_FILE("error reading p value\n");
555 read_mpbin(&st->p,b,length);
559 fatal_perror("rsa-private (%s:%d): ferror",loc.file,loc.line);
563 * Now verify the validity of the key, and set up the auxiliary
564 * values for fast CRT signing.
567 if (do_validity_check) {
568 /* Verify that p*q is equal to n. */
569 mpz_mul(&tmp, &st->p, &st->q);
570 if (mpz_cmp(&tmp, &st->n) != 0)
574 * Verify that d*e is congruent to 1 mod (p-1), and mod
575 * (q-1). This is equivalent to it being congruent to 1 mod
576 * lambda(n) = lcm(p-1,q-1). The usual `textbook' condition,
577 * that d e == 1 (mod (p-1)(q-1)) is sufficient, but not
578 * actually necessary.
580 mpz_mul(&tmp, &d, &e);
581 mpz_sub_ui(&tmp2, &st->p, 1);
582 mpz_mod(&tmp3, &tmp, &tmp2);
583 if (mpz_cmp_si(&tmp3, 1) != 0)
585 mpz_sub_ui(&tmp2, &st->q, 1);
586 mpz_mod(&tmp3, &tmp, &tmp2);
587 if (mpz_cmp_si(&tmp3, 1) != 0)
590 /* Verify that q*iqmp is congruent to 1 mod p. */
591 mpz_mul(&tmp, &st->q, &iqmp);
592 mpz_mod(&tmp2, &tmp, &st->p);
593 if (mpz_cmp_si(&tmp2, 1) != 0)
596 /* Now we know the key is valid (or we don't care). */
600 * Now we compute auxiliary values dp, dq and w to allow us
601 * to use the CRT optimisation when signing.
603 * dp == d mod (p-1) so that a^dp == a^d mod p, for all a
604 * dq == d mod (q-1) similarly mod q
605 * w == iqmp * q so that w == 0 mod q, and w == 1 mod p
607 mpz_sub_ui(&tmp, &st->p, 1);
608 mpz_mod(&st->dp, &d, &tmp);
609 mpz_sub_ui(&tmp, &st->q, 1);
610 mpz_mod(&st->dq, &d, &tmp);
611 mpz_mul(&st->w, &iqmp, &st->q);
615 LDFATAL("file does not contain a "
634 if (st) rsapriv_dispose(st);
639 static bool_t postreadcheck_tryload(struct load_ctx *l, FILE *f)
642 if (feof(f)) { load_error(l,0,0,"eof mid-integer"); return False; }
646 bool_t rsa1_loadpriv(const struct sigscheme_info *algo,
647 struct buffer_if *privkeydata,
648 struct sigprivkey_if **sigpriv_r,
652 struct rsapriv *st=0;
654 f=fmemopen(privkeydata->start,privkeydata->size,"r");
656 slilog(log,M_ERR,"failed to fmemopen private key file\n");
661 loc.file="dynamically loaded";
664 struct load_ctx l[1];
665 l->verror=verror_tryload;
666 l->postreadcheck=postreadcheck_tryload;
668 l->u.tryload.log=log;
670 st=rsa_loadpriv_core(l,f,loc,False);
671 if (!st) goto error_out;
675 if (st) { free(st); st=0; }
678 if (!st) return False;
683 static bool_t postreadcheck_apply(struct load_ctx *l, FILE *f)
685 cfgfile_postreadcheck(*l->loc,f);
689 static list_t *rsapriv_apply(closure_t *self, struct cloc loc, dict_t *context,
696 struct load_ctx l[1];
698 l->verror=verror_cfgfatal;
699 l->postreadcheck=postreadcheck_apply;
702 /* Argument is filename pointing to SSH1 private key file */
705 if (i->type!=t_string) {
706 cfgfatal(i->loc,"rsa-private","first argument must be a string\n");
708 filename=i->data.string;
710 filename=NULL; /* Make compiler happy */
711 cfgfatal(i->loc,"rsa-private","you must provide a filename\n");
714 f=fopen(filename,"rb");
716 if (just_check_config) {
717 Message(M_WARNING,"rsa-private (%s:%d): cannot open keyfile "
718 "\"%s\"; assuming it's valid while we check the "
719 "rest of the configuration\n",loc.file,loc.line,filename);
721 fatal_perror("rsa-private (%s:%d): cannot open file \"%s\"",
722 loc.file,loc.line,filename);
726 bool_t do_validity_check=True;
728 if (i && i->type==t_bool && i->data.bool==False) {
729 Message(M_INFO,"rsa-private (%s:%d): skipping RSA key validity "
730 "check\n",loc.file,loc.line);
731 do_validity_check=False;
734 st=rsa_loadpriv_core(l,f,loc,do_validity_check);
736 return new_closure(&st->cl);
739 void rsa_module(dict_t *dict)
741 add_closure(dict,"rsa-private",rsapriv_apply);
742 add_closure(dict,"rsa-public",rsapub_apply);