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 struct rsapriv_load_ctx {
49 void (*verror)(struct rsapriv_load_ctx *l,
50 FILE *maybe_f, bool_t unsup,
51 const char *message, va_list args);
52 bool_t (*postreadcheck)(struct rsapriv_load_ctx *l, FILE *f);
64 static void verror_tryload(struct rsapriv_load_ctx *l,
65 FILE *maybe_f, bool_t unsup,
66 const char *message, va_list args)
68 int class=unsup ? M_DEBUG : M_ERR;
69 slilog_part(l->u.tryload.log,class,"rsa1priv load: ");
70 vslilog(l->u.tryload.log,class,message,args);
73 static void verror_cfgfatal(struct rsapriv_load_ctx *l,
74 FILE *maybe_f, bool_t unsup,
75 const char *message, va_list args)
77 vcfgfatal_maybefile(maybe_f,l->u.apply.loc,"rsa-private",message,args);
82 struct sigprivkey_if ops;
84 struct rsacommon common;
92 struct sigpubkey_if ops;
94 struct rsacommon common;
98 /* Sign data. NB data must be smaller than modulus */
100 #define RSA_MAX_MODBYTES 2048
101 /* The largest modulus I've seen is 15360 bits, which works out at 1920
102 * bytes. Using keys this big is quite implausible, but it doesn't cost us
103 * much to support them.
106 static const char *hexchars="0123456789abcdef";
108 static void rsa_sethash(struct rsacommon *c, struct hash_if *hash,
109 const struct hash_if **in_ops)
112 c->hashbuf=safe_malloc(hash->hlen, "generate_msg");
115 static void rsa_pub_sethash(void *sst, struct hash_if *hash)
117 struct rsapub *st=sst;
118 rsa_sethash(&st->common, hash, &st->ops.hash);
120 static void rsa_priv_sethash(void *sst, struct hash_if *hash)
122 struct rsapriv *st=sst;
123 rsa_sethash(&st->common, hash, &st->ops.hash);
125 static void rsacommon_dispose(struct rsacommon *c)
130 static void emsa_pkcs1(MP_INT *n, MP_INT *m,
131 const uint8_t *data, int32_t datalen)
133 char buff[2*RSA_MAX_MODBYTES + 1];
136 /* RSA PKCS#1 v1.5 signature padding:
138 * <------------ msize hex digits ---------->
140 * 00 01 ff ff .... ff ff 00 vv vv vv .... vv
144 * = datalen*2 hex digits
146 * NB that according to PKCS#1 v1.5 we're supposed to include a
147 * hash function OID in the data. We don't do that (because we
148 * don't have the hash function OID to hand here), thus violating
149 * the spec in a way that affects interop but not security.
154 msize=mpz_sizeinbase(n, 16);
156 if (datalen*2+6>=msize) {
157 fatal("rsa: message too big");
162 for (i=0; i<datalen; i++) {
163 buff[msize+(-datalen+i)*2]=hexchars[(data[i]&0xf0)>>4];
164 buff[msize+(-datalen+i)*2+1]=hexchars[data[i]&0xf];
167 buff[msize-datalen*2-2]= '0';
168 buff[msize-datalen*2-1]= '0';
170 for (i=4; i<msize-datalen*2-2; i++)
175 mpz_set_str(m, buff, 16);
178 static bool_t rsa_sign(void *sst, uint8_t *data, int32_t datalen,
179 struct buffer_if *msg)
181 struct rsapriv *st=sst;
182 MP_INT a, b, u, v, tmp, tmp2;
183 string_t signature = 0;
189 hash_hash(st->ops.hash,data,datalen,st->common.hashbuf);
190 /* Construct the message representative. */
191 emsa_pkcs1(&st->n, &a, st->common.hashbuf, st->ops.hash->hlen);
194 * Produce an RSA signature (a^d mod n) using the Chinese
195 * Remainder Theorem. We compute:
197 * u = a^dp mod p (== a^d mod p, since dp == d mod (p-1))
198 * v = a^dq mod q (== a^d mod q, similarly)
200 * We also know w == iqmp * q, which has the property that w ==
201 * 0 mod q and w == 1 mod p. So (1-w) has the reverse property
202 * (congruent to 0 mod p and to 1 mod q). Hence we now compute
204 * b = w * u + (1-w) * v
207 * so that b is congruent to a^d both mod p and mod q. Hence b,
208 * reduced mod n, is the required signature.
215 mpz_powm_sec(&u, &a, &st->dp, &st->p);
216 mpz_powm_sec(&v, &a, &st->dq, &st->q);
217 mpz_sub(&tmp, &u, &v);
218 mpz_mul(&tmp2, &tmp, &st->w);
219 mpz_add(&tmp, &tmp2, &v);
220 mpz_mod(&b, &tmp, &st->n);
227 signature=write_mpstring(&b);
229 uint8_t *op = buf_append(msg,2);
230 if (!op) { ok=False; goto out; }
231 size_t l = strlen(signature);
234 op = buf_append(msg,l);
235 if (!op) { ok=False; goto out; }
236 memcpy(op, signature, l);
247 static bool_t rsa_sig_unpick(void *sst, struct buffer_if *msg,
248 struct alg_msg_data *sig)
250 uint8_t *lp = buf_unprepend(msg, 2);
251 if (!lp) return False;
252 sig->len = get_uint16(lp);
253 sig->start = buf_unprepend(msg, sig->len);
254 if (!sig->start) return False;
256 /* In `rsa_sig_check' below, we assume that we can write a nul
257 * terminator following the signature. Make sure there's enough space.
259 if (msg->start >= msg->base + msg->alloclen)
265 static sig_checksig_fn rsa_sig_check;
266 static bool_t rsa_sig_check(void *sst, uint8_t *data, int32_t datalen,
267 const struct alg_msg_data *sig)
269 struct rsapub *st=sst;
277 hash_hash(st->ops.hash,data,datalen,st->common.hashbuf);
278 emsa_pkcs1(&st->n, &a, st->common.hashbuf, st->ops.hash->hlen);
280 /* Terminate signature with a '0' - already checked that this will fit */
281 int save = sig->start[sig->len];
282 sig->start[sig->len] = 0;
283 mpz_set_str(&b, sig->start, 16);
284 sig->start[sig->len] = save;
286 mpz_powm(&c, &b, &st->e, &st->n);
288 ok=(mpz_cmp(&a, &c)==0);
297 static void rsapub_dispose(void *sst) {
298 struct rsapub *st=sst;
302 rsacommon_dispose(&st->common);
306 static list_t *rsapub_apply(closure_t *self, struct cloc loc, dict_t *context,
314 st->cl.description="rsapub";
315 st->cl.type=CL_SIGPUBKEY;
317 st->cl.interface=&st->ops;
319 st->ops.sethash=rsa_pub_sethash;
320 st->common.hashbuf=NULL;
321 st->ops.unpick=rsa_sig_unpick;
322 st->ops.check=rsa_sig_check;
324 st->ops.dispose=rsapub_dispose;
329 if (i->type!=t_string) {
330 cfgfatal(i->loc,"rsa-public","first argument must be a string\n");
333 if (mpz_init_set_str(&st->e,e,10)!=0) {
334 cfgfatal(i->loc,"rsa-public","encryption key \"%s\" is not a "
335 "decimal number string\n",e);
338 cfgfatal(loc,"rsa-public","you must provide an encryption key\n");
340 if (mpz_sizeinbase(&st->e, 256) > RSA_MAX_MODBYTES) {
341 cfgfatal(loc, "rsa-public", "implausibly large public exponent\n");
346 if (i->type!=t_string) {
347 cfgfatal(i->loc,"rsa-public","second argument must be a string\n");
350 if (mpz_init_set_str(&st->n,n,10)!=0) {
351 cfgfatal(i->loc,"rsa-public","modulus \"%s\" is not a decimal "
352 "number string\n",n);
355 cfgfatal(loc,"rsa-public","you must provide a modulus\n");
357 if (mpz_sizeinbase(&st->n, 256) > RSA_MAX_MODBYTES) {
358 cfgfatal(loc, "rsa-public", "implausibly large modulus\n");
360 return new_closure(&st->cl);
363 static void load_error(struct rsapriv_load_ctx *l, FILE *maybe_f,
364 bool_t unsup, const char *fmt, ...)
368 l->verror(l,maybe_f,unsup,fmt,al);
372 #define LDFATAL(...) ({ load_error(l,0,0,__VA_ARGS__); goto error_out; })
373 #define LDUNSUP(...) ({ load_error(l,0,1,__VA_ARGS__); goto error_out; })
374 #define LDFATAL_FILE(...) ({ load_error(l,f,0,__VA_ARGS__); goto error_out; })
375 #define LDUNSUP_FILE(...) ({ load_error(l,f,1,__VA_ARGS__); goto error_out; })
376 #define FREE(b) ({ free((b)); (b)=0; })
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 rsapriv_load_ctx *l, FILE *f)
393 static uint16_t keyfile_get_16(struct rsapriv_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 rsapriv_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 rsapriv_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,
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");
663 loc.file="dynamically loaded";
666 struct rsapriv_load_ctx l[1];
667 l->verror=verror_tryload;
668 l->postreadcheck=postreadcheck_tryload;
669 l->u.tryload.log=log;
671 st=rsa_loadpriv_core(l,f,loc,False);
672 if (!st) goto error_out;
676 if (st) { free(st); st=0; }
679 if (!st) return False;
684 static bool_t postreadcheck_apply(struct rsapriv_load_ctx *l, FILE *f)
686 cfgfile_postreadcheck(l->u.apply.loc,f);
690 static list_t *rsapriv_apply(closure_t *self, struct cloc loc, dict_t *context,
697 struct rsapriv_load_ctx l[1];
699 l->verror=verror_cfgfatal;
700 l->postreadcheck=postreadcheck_apply;
703 /* Argument is filename pointing to SSH1 private key file */
706 if (i->type!=t_string) {
707 cfgfatal(i->loc,"rsa-private","first argument must be a string\n");
709 filename=i->data.string;
711 filename=NULL; /* Make compiler happy */
712 cfgfatal(i->loc,"rsa-private","you must provide a filename\n");
715 f=fopen(filename,"rb");
717 if (just_check_config) {
718 Message(M_WARNING,"rsa-private (%s:%d): cannot open keyfile "
719 "\"%s\"; assuming it's valid while we check the "
720 "rest of the configuration\n",loc.file,loc.line,filename);
722 fatal_perror("rsa-private (%s:%d): cannot open file \"%s\"",
723 loc.file,loc.line,filename);
727 bool_t do_validity_check=True;
729 if (i && i->type==t_bool && i->data.bool==False) {
730 Message(M_INFO,"rsa-private (%s:%d): skipping RSA key validity "
731 "check\n",loc.file,loc.line);
732 do_validity_check=False;
735 st=rsa_loadpriv_core(l,f,loc,do_validity_check);
737 return new_closure(&st->cl);
740 void rsa_module(dict_t *dict)
742 add_closure(dict,"rsa-private",rsapriv_apply);
743 add_closure(dict,"rsa-public",rsapub_apply);