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)
48 #define FREE(b) ({ free((b)); (b)=0; })
51 void (*verror)(struct load_ctx *l,
52 FILE *maybe_f, bool_t unsup,
53 const char *message, va_list args);
54 bool_t (*postreadcheck)(struct load_ctx *l, FILE *f);
65 static void verror_tryload(struct load_ctx *l,
66 FILE *maybe_f, bool_t unsup,
67 const char *message, va_list args)
69 int class=unsup ? M_DEBUG : M_ERR;
70 slilog_part(l->u.tryload.log,class,"%s: ",l->what);
71 vslilog(l->u.tryload.log,class,message,args);
74 static void verror_cfgfatal(struct load_ctx *l,
75 FILE *maybe_f, bool_t unsup,
76 const char *message, va_list args)
78 vcfgfatal_maybefile(maybe_f,*l->loc,l->what,message,args);
83 struct sigprivkey_if ops;
85 struct rsacommon common;
93 struct sigpubkey_if ops;
95 struct rsacommon common;
99 /* Sign data. NB data must be smaller than modulus */
101 #define RSA_MAX_MODBYTES 2048
102 /* The largest modulus I've seen is 15360 bits, which works out at 1920
103 * bytes. Using keys this big is quite implausible, but it doesn't cost us
104 * much to support them.
107 static const char *hexchars="0123456789abcdef";
109 static void rsa_sethash(struct rsacommon *c, struct hash_if *hash,
110 const struct hash_if **in_ops)
113 c->hashbuf=safe_malloc(hash->hlen, "generate_msg");
116 static void rsa_pub_sethash(void *sst, struct hash_if *hash)
118 struct rsapub *st=sst;
119 rsa_sethash(&st->common, hash, &st->ops.hash);
121 static void rsa_priv_sethash(void *sst, struct hash_if *hash)
123 struct rsapriv *st=sst;
124 rsa_sethash(&st->common, hash, &st->ops.hash);
126 static void rsacommon_dispose(struct rsacommon *c)
131 static void emsa_pkcs1(MP_INT *n, MP_INT *m,
132 const uint8_t *data, int32_t datalen)
134 char buff[2*RSA_MAX_MODBYTES + 1];
137 /* RSA PKCS#1 v1.5 signature padding:
139 * <------------ msize hex digits ---------->
141 * 00 01 ff ff .... ff ff 00 vv vv vv .... vv
145 * = datalen*2 hex digits
147 * NB that according to PKCS#1 v1.5 we're supposed to include a
148 * hash function OID in the data. We don't do that (because we
149 * don't have the hash function OID to hand here), thus violating
150 * the spec in a way that affects interop but not security.
155 msize=mpz_sizeinbase(n, 16);
157 if (datalen*2+6>=msize) {
158 fatal("rsa: message too big");
163 for (i=0; i<datalen; i++) {
164 buff[msize+(-datalen+i)*2]=hexchars[(data[i]&0xf0)>>4];
165 buff[msize+(-datalen+i)*2+1]=hexchars[data[i]&0xf];
168 buff[msize-datalen*2-2]= '0';
169 buff[msize-datalen*2-1]= '0';
171 for (i=4; i<msize-datalen*2-2; i++)
176 mpz_set_str(m, buff, 16);
179 static bool_t rsa_sign(void *sst, uint8_t *data, int32_t datalen,
180 struct buffer_if *msg)
182 struct rsapriv *st=sst;
183 MP_INT a, b, u, v, tmp, tmp2;
184 string_t signature = 0;
190 hash_hash(st->ops.hash,data,datalen,st->common.hashbuf);
191 /* Construct the message representative. */
192 emsa_pkcs1(&st->n, &a, st->common.hashbuf, st->ops.hash->hlen);
195 * Produce an RSA signature (a^d mod n) using the Chinese
196 * Remainder Theorem. We compute:
198 * u = a^dp mod p (== a^d mod p, since dp == d mod (p-1))
199 * v = a^dq mod q (== a^d mod q, similarly)
201 * We also know w == iqmp * q, which has the property that w ==
202 * 0 mod q and w == 1 mod p. So (1-w) has the reverse property
203 * (congruent to 0 mod p and to 1 mod q). Hence we now compute
205 * b = w * u + (1-w) * v
208 * so that b is congruent to a^d both mod p and mod q. Hence b,
209 * reduced mod n, is the required signature.
216 mpz_powm_sec(&u, &a, &st->dp, &st->p);
217 mpz_powm_sec(&v, &a, &st->dq, &st->q);
218 mpz_sub(&tmp, &u, &v);
219 mpz_mul(&tmp2, &tmp, &st->w);
220 mpz_add(&tmp, &tmp2, &v);
221 mpz_mod(&b, &tmp, &st->n);
228 signature=write_mpstring(&b);
230 uint8_t *op = buf_append(msg,2);
231 if (!op) { ok=False; goto out; }
232 size_t l = strlen(signature);
235 op = buf_append(msg,l);
236 if (!op) { ok=False; goto out; }
237 memcpy(op, signature, l);
248 static bool_t rsa_sig_unpick(void *sst, struct buffer_if *msg,
249 struct alg_msg_data *sig)
251 uint8_t *lp = buf_unprepend(msg, 2);
252 if (!lp) return False;
253 sig->len = get_uint16(lp);
254 sig->start = buf_unprepend(msg, sig->len);
255 if (!sig->start) return False;
257 /* In `rsa_sig_check' below, we assume that we can write a nul
258 * terminator following the signature. Make sure there's enough space.
260 if (msg->start >= msg->base + msg->alloclen)
266 static sig_checksig_fn rsa_sig_check;
267 static bool_t rsa_sig_check(void *sst, uint8_t *data, int32_t datalen,
268 const struct alg_msg_data *sig)
270 struct rsapub *st=sst;
278 hash_hash(st->ops.hash,data,datalen,st->common.hashbuf);
279 emsa_pkcs1(&st->n, &a, st->common.hashbuf, st->ops.hash->hlen);
281 /* Terminate signature with a '0' - already checked that this will fit */
282 int save = sig->start[sig->len];
283 sig->start[sig->len] = 0;
284 mpz_set_str(&b, sig->start, 16);
285 sig->start[sig->len] = save;
287 mpz_powm(&c, &b, &st->e, &st->n);
289 ok=(mpz_cmp(&a, &c)==0);
298 static void rsapub_dispose(void *sst) {
299 struct rsapub *st=sst;
303 rsacommon_dispose(&st->common);
307 static list_t *rsapub_apply(closure_t *self, struct cloc loc, dict_t *context,
315 st->cl.description="rsapub";
316 st->cl.type=CL_SIGPUBKEY;
318 st->cl.interface=&st->ops;
320 st->ops.sethash=rsa_pub_sethash;
321 st->common.hashbuf=NULL;
322 st->ops.unpick=rsa_sig_unpick;
323 st->ops.check=rsa_sig_check;
325 st->ops.dispose=rsapub_dispose;
330 if (i->type!=t_string) {
331 cfgfatal(i->loc,"rsa-public","first argument must be a string\n");
334 if (mpz_init_set_str(&st->e,e,10)!=0) {
335 cfgfatal(i->loc,"rsa-public","encryption key \"%s\" is not a "
336 "decimal number string\n",e);
339 cfgfatal(loc,"rsa-public","you must provide an encryption key\n");
341 if (mpz_sizeinbase(&st->e, 256) > RSA_MAX_MODBYTES) {
342 cfgfatal(loc, "rsa-public", "implausibly large public exponent\n");
347 if (i->type!=t_string) {
348 cfgfatal(i->loc,"rsa-public","second argument must be a string\n");
351 if (mpz_init_set_str(&st->n,n,10)!=0) {
352 cfgfatal(i->loc,"rsa-public","modulus \"%s\" is not a decimal "
353 "number string\n",n);
356 cfgfatal(loc,"rsa-public","you must provide a modulus\n");
358 if (mpz_sizeinbase(&st->n, 256) > RSA_MAX_MODBYTES) {
359 cfgfatal(loc, "rsa-public", "implausibly large modulus\n");
361 return new_closure(&st->cl);
364 static void load_error(struct load_ctx *l, FILE *maybe_f,
365 bool_t unsup, const char *fmt, ...)
369 l->verror(l,maybe_f,unsup,fmt,al);
373 #define LDFATAL(...) ({ load_error(l,0,0,__VA_ARGS__); goto error_out; })
374 #define LDUNSUP(...) ({ load_error(l,0,1,__VA_ARGS__); goto error_out; })
375 #define LDFATAL_FILE(...) ({ load_error(l,f,0,__VA_ARGS__); goto error_out; })
376 #define LDUNSUP_FILE(...) ({ load_error(l,f,1,__VA_ARGS__); goto error_out; })
377 #define KEYFILE_GET(is) ({ \
378 uint##is##_t keyfile_get_tmp=keyfile_get_##is(l,f); \
379 if (!l->postreadcheck(l,f)) goto error_out; \
383 static uint32_t keyfile_get_32(struct load_ctx *l, FILE *f)
393 static uint16_t keyfile_get_16(struct load_ctx *l, FILE *f)
401 static void rsapriv_dispose(void *sst)
403 struct rsapriv *st=sst;
405 mpz_clear(&st->p); mpz_clear(&st->dp);
406 mpz_clear(&st->q); mpz_clear(&st->dq);
408 rsacommon_dispose(&st->common);
412 static struct rsapriv *rsa_loadpriv_core(struct load_ctx *l,
413 FILE *f, struct cloc loc,
414 bool_t do_validity_check)
416 struct rsapriv *st=0;
420 MP_INT e,d,iqmp,tmp,tmp2,tmp3;
431 st->cl.description="rsapriv";
432 st->cl.type=CL_SIGPRIVKEY;
434 st->cl.interface=&st->ops;
436 st->ops.sethash=rsa_priv_sethash;
437 st->common.hashbuf=NULL;
438 st->ops.sign=rsa_sign;
440 st->ops.dispose=rsapriv_dispose;
450 assert(just_check_config);
454 /* Check that the ID string is correct */
455 length=strlen(AUTHFILE_ID_STRING)+1;
456 b=safe_malloc(length,"rsapriv_apply");
457 if (fread(b,length,1,f)!=1 || memcmp(b,AUTHFILE_ID_STRING,length)!=0) {
458 LDUNSUP_FILE("failed to read magic ID"
459 " string from SSH1 private keyfile\n");
463 cipher_type=fgetc(f);
464 KEYFILE_GET(32); /* "Reserved data" */
465 if (cipher_type != 0) {
466 LDUNSUP("we don't support encrypted keyfiles\n");
469 /* Read the public key */
470 KEYFILE_GET(32); /* Not sure what this is */
471 length=(KEYFILE_GET(16)+7)/8;
472 if (length>RSA_MAX_MODBYTES) {
473 LDFATAL("implausible length %ld for modulus\n",
476 b=safe_malloc(length,"rsapriv_apply");
477 if (fread(b,length,1,f) != 1) {
478 LDFATAL_FILE("error reading modulus\n");
480 read_mpbin(&st->n,b,length);
482 length=(KEYFILE_GET(16)+7)/8;
483 if (length>RSA_MAX_MODBYTES) {
484 LDFATAL("implausible length %ld for e\n",length);
486 b=safe_malloc(length,"rsapriv_apply");
487 if (fread(b,length,1,f)!=1) {
488 LDFATAL_FILE("error reading e\n");
490 read_mpbin(&e,b,length);
493 length=KEYFILE_GET(32);
495 LDFATAL("implausibly long (%ld) key comment\n",
498 c=safe_malloc(length+1,"rsapriv_apply");
499 if (fread(c,length,1,f)!=1) {
500 LDFATAL_FILE("error reading key comment\n");
504 /* Check that the next two pairs of characters are identical - the
505 keyfile is not encrypted, so they should be */
507 if (KEYFILE_GET(16) != KEYFILE_GET(16)) {
508 LDFATAL("corrupt keyfile\n");
512 length=(KEYFILE_GET(16)+7)/8;
513 if (length>RSA_MAX_MODBYTES) {
514 LDFATAL("implausibly long (%ld) decryption key\n",
517 b=safe_malloc(length,"rsapriv_apply");
518 if (fread(b,length,1,f)!=1) {
519 LDFATAL_FILE("error reading decryption key\n");
521 read_mpbin(&d,b,length);
523 /* Read iqmp (inverse of q mod p) */
524 length=(KEYFILE_GET(16)+7)/8;
525 if (length>RSA_MAX_MODBYTES) {
526 LDFATAL("implausibly long (%ld)"
527 " iqmp auxiliary value\n", length);
529 b=safe_malloc(length,"rsapriv_apply");
530 if (fread(b,length,1,f)!=1) {
531 LDFATAL_FILE("error reading decryption key\n");
533 read_mpbin(&iqmp,b,length);
535 /* Read q (the smaller of the two primes) */
536 length=(KEYFILE_GET(16)+7)/8;
537 if (length>RSA_MAX_MODBYTES) {
538 LDFATAL("implausibly long (%ld) q value\n",
541 b=safe_malloc(length,"rsapriv_apply");
542 if (fread(b,length,1,f)!=1) {
543 LDFATAL_FILE("error reading q value\n");
545 read_mpbin(&st->q,b,length);
547 /* Read p (the larger of the two primes) */
548 length=(KEYFILE_GET(16)+7)/8;
549 if (length>RSA_MAX_MODBYTES) {
550 LDFATAL("implausibly long (%ld) p value\n",
553 b=safe_malloc(length,"rsapriv_apply");
554 if (fread(b,length,1,f)!=1) {
555 LDFATAL_FILE("error reading p value\n");
557 read_mpbin(&st->p,b,length);
561 fatal_perror("rsa-private (%s:%d): ferror",loc.file,loc.line);
565 * Now verify the validity of the key, and set up the auxiliary
566 * values for fast CRT signing.
569 if (do_validity_check) {
570 /* Verify that p*q is equal to n. */
571 mpz_mul(&tmp, &st->p, &st->q);
572 if (mpz_cmp(&tmp, &st->n) != 0)
576 * Verify that d*e is congruent to 1 mod (p-1), and mod
577 * (q-1). This is equivalent to it being congruent to 1 mod
578 * lambda(n) = lcm(p-1,q-1). The usual `textbook' condition,
579 * that d e == 1 (mod (p-1)(q-1)) is sufficient, but not
580 * actually necessary.
582 mpz_mul(&tmp, &d, &e);
583 mpz_sub_ui(&tmp2, &st->p, 1);
584 mpz_mod(&tmp3, &tmp, &tmp2);
585 if (mpz_cmp_si(&tmp3, 1) != 0)
587 mpz_sub_ui(&tmp2, &st->q, 1);
588 mpz_mod(&tmp3, &tmp, &tmp2);
589 if (mpz_cmp_si(&tmp3, 1) != 0)
592 /* Verify that q*iqmp is congruent to 1 mod p. */
593 mpz_mul(&tmp, &st->q, &iqmp);
594 mpz_mod(&tmp2, &tmp, &st->p);
595 if (mpz_cmp_si(&tmp2, 1) != 0)
598 /* Now we know the key is valid (or we don't care). */
602 * Now we compute auxiliary values dp, dq and w to allow us
603 * to use the CRT optimisation when signing.
605 * dp == d mod (p-1) so that a^dp == a^d mod p, for all a
606 * dq == d mod (q-1) similarly mod q
607 * w == iqmp * q so that w == 0 mod q, and w == 1 mod p
609 mpz_sub_ui(&tmp, &st->p, 1);
610 mpz_mod(&st->dp, &d, &tmp);
611 mpz_sub_ui(&tmp, &st->q, 1);
612 mpz_mod(&st->dq, &d, &tmp);
613 mpz_mul(&st->w, &iqmp, &st->q);
617 LDFATAL("file does not contain a "
636 if (st) rsapriv_dispose(st);
641 static bool_t postreadcheck_tryload(struct load_ctx *l, FILE *f)
644 if (feof(f)) { load_error(l,0,0,"eof mid-integer"); return False; }
648 bool_t rsa1_loadpriv(const struct sigscheme_info *algo,
649 struct buffer_if *privkeydata,
650 struct sigprivkey_if **sigpriv_r,
651 struct log_if *log, struct cloc loc)
654 struct rsapriv *st=0;
656 f=fmemopen(privkeydata->start,privkeydata->size,"r");
658 slilog(log,M_ERR,"failed to fmemopen private key file\n");
662 struct load_ctx l[1];
663 l->what="rsa1priv load";
664 l->verror=verror_tryload;
665 l->postreadcheck=postreadcheck_tryload;
667 l->u.tryload.log=log;
669 st=rsa_loadpriv_core(l,f,loc,False);
670 if (!st) goto error_out;
674 if (st) { free(st); st=0; }
677 if (!st) return False;
682 static bool_t postreadcheck_apply(struct load_ctx *l, FILE *f)
684 cfgfile_postreadcheck(*l->loc,f);
688 static list_t *rsapriv_apply(closure_t *self, struct cloc loc, dict_t *context,
695 struct load_ctx l[1];
697 l->what="rsa-private";
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);