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;
92 #define RSAPUB_BNS(each) \
93 each(0,e,"public exponent") \
98 struct sigpubkey_if ops;
100 struct rsacommon common;
104 /* Sign data. NB data must be smaller than modulus */
106 #define RSA_MAX_MODBYTES 2048
107 /* The largest modulus I've seen is 15360 bits, which works out at 1920
108 * bytes. Using keys this big is quite implausible, but it doesn't cost us
109 * much to support them.
112 static const char *hexchars="0123456789abcdef";
114 static void rsa_sethash(struct rsacommon *c, struct hash_if *hash,
115 const struct hash_if **in_ops)
118 c->hashbuf=safe_malloc(hash->hlen, "generate_msg");
121 static void rsa_pub_sethash(void *sst, struct hash_if *hash)
123 struct rsapub *st=sst;
124 rsa_sethash(&st->common, hash, &st->ops.hash);
126 static void rsa_priv_sethash(void *sst, struct hash_if *hash)
128 struct rsapriv *st=sst;
129 rsa_sethash(&st->common, hash, &st->ops.hash);
131 static void rsacommon_dispose(struct rsacommon *c)
136 static void emsa_pkcs1(MP_INT *n, MP_INT *m,
137 const uint8_t *data, int32_t datalen)
139 char buff[2*RSA_MAX_MODBYTES + 1];
142 /* RSA PKCS#1 v1.5 signature padding:
144 * <------------ msize hex digits ---------->
146 * 00 01 ff ff .... ff ff 00 vv vv vv .... vv
150 * = datalen*2 hex digits
152 * NB that according to PKCS#1 v1.5 we're supposed to include a
153 * hash function OID in the data. We don't do that (because we
154 * don't have the hash function OID to hand here), thus violating
155 * the spec in a way that affects interop but not security.
160 msize=mpz_sizeinbase(n, 16);
162 if (datalen*2+6>=msize) {
163 fatal("rsa: message too big");
168 for (i=0; i<datalen; i++) {
169 buff[msize+(-datalen+i)*2]=hexchars[(data[i]&0xf0)>>4];
170 buff[msize+(-datalen+i)*2+1]=hexchars[data[i]&0xf];
173 buff[msize-datalen*2-2]= '0';
174 buff[msize-datalen*2-1]= '0';
176 for (i=4; i<msize-datalen*2-2; i++)
181 mpz_set_str(m, buff, 16);
184 static bool_t rsa_sign(void *sst, uint8_t *data, int32_t datalen,
185 struct buffer_if *msg)
187 struct rsapriv *st=sst;
188 MP_INT a, b, u, v, tmp, tmp2;
189 string_t signature = 0;
195 hash_hash(st->ops.hash,data,datalen,st->common.hashbuf);
196 /* Construct the message representative. */
197 emsa_pkcs1(&st->n, &a, st->common.hashbuf, st->ops.hash->hlen);
200 * Produce an RSA signature (a^d mod n) using the Chinese
201 * Remainder Theorem. We compute:
203 * u = a^dp mod p (== a^d mod p, since dp == d mod (p-1))
204 * v = a^dq mod q (== a^d mod q, similarly)
206 * We also know w == iqmp * q, which has the property that w ==
207 * 0 mod q and w == 1 mod p. So (1-w) has the reverse property
208 * (congruent to 0 mod p and to 1 mod q). Hence we now compute
210 * b = w * u + (1-w) * v
213 * so that b is congruent to a^d both mod p and mod q. Hence b,
214 * reduced mod n, is the required signature.
221 mpz_powm_sec(&u, &a, &st->dp, &st->p);
222 mpz_powm_sec(&v, &a, &st->dq, &st->q);
223 mpz_sub(&tmp, &u, &v);
224 mpz_mul(&tmp2, &tmp, &st->w);
225 mpz_add(&tmp, &tmp2, &v);
226 mpz_mod(&b, &tmp, &st->n);
233 signature=write_mpstring(&b);
235 uint8_t *op = buf_append(msg,2);
236 if (!op) { ok=False; goto out; }
237 size_t l = strlen(signature);
240 op = buf_append(msg,l);
241 if (!op) { ok=False; goto out; }
242 memcpy(op, signature, l);
253 static bool_t rsa_sig_unpick(void *sst, struct buffer_if *msg,
254 struct alg_msg_data *sig)
256 uint8_t *lp = buf_unprepend(msg, 2);
257 if (!lp) return False;
258 sig->len = get_uint16(lp);
259 sig->start = buf_unprepend(msg, sig->len);
260 if (!sig->start) return False;
262 /* In `rsa_sig_check' below, we assume that we can write a nul
263 * terminator following the signature. Make sure there's enough space.
265 if (msg->start >= msg->base + msg->alloclen)
271 static sig_checksig_fn rsa_sig_check;
272 static bool_t rsa_sig_check(void *sst, uint8_t *data, int32_t datalen,
273 const struct alg_msg_data *sig)
275 struct rsapub *st=sst;
283 hash_hash(st->ops.hash,data,datalen,st->common.hashbuf);
284 emsa_pkcs1(&st->n, &a, st->common.hashbuf, st->ops.hash->hlen);
286 /* Terminate signature with a '0' - already checked that this will fit */
287 int save = sig->start[sig->len];
288 sig->start[sig->len] = 0;
289 mpz_set_str(&b, sig->start, 16);
290 sig->start[sig->len] = save;
292 mpz_powm(&c, &b, &st->e, &st->n);
294 ok=(mpz_cmp(&a, &c)==0);
303 static void rsapub_dispose(void *sst) {
304 struct rsapub *st=sst;
308 rsacommon_dispose(&st->common);
312 static list_t *rsapub_apply(closure_t *self, struct cloc loc, dict_t *context,
319 st->cl.description="rsapub";
320 st->cl.type=CL_SIGPUBKEY;
322 st->cl.interface=&st->ops;
324 st->ops.sethash=rsa_pub_sethash;
325 st->common.hashbuf=NULL;
326 st->ops.unpick=rsa_sig_unpick;
327 st->ops.check=rsa_sig_check;
329 st->ops.dispose=rsapub_dispose;
332 #define RSAPUB_APPLY_GETBN(ix,en,what) \
334 i=list_elem(args,ix); \
336 if (i->type!=t_string) { \
337 cfgfatal(i->loc,"rsa-public",what " must be a string\n"); \
340 if (mpz_init_set_str(&st->en,en,10)!=0) { \
341 cfgfatal(i->loc,"rsa-public", what " \"%s\" is not a " \
342 "decimal number string\n",en); \
345 cfgfatal(loc,"rsa-public","you must provide the " what "\n"); \
347 if (mpz_sizeinbase(&st->en, 256) > RSA_MAX_MODBYTES) { \
348 cfgfatal(loc, "rsa-public", "implausibly large " what "\n"); \
351 RSAPUB_BNS(RSAPUB_APPLY_GETBN)
353 return new_closure(&st->cl);
356 static void load_error(struct load_ctx *l, FILE *maybe_f,
357 bool_t unsup, const char *fmt, ...)
361 l->verror(l,maybe_f,unsup,fmt,al);
365 #define LDFATAL(...) ({ load_error(l,0,0,__VA_ARGS__); goto error_out; })
366 #define LDUNSUP(...) ({ load_error(l,0,1,__VA_ARGS__); goto error_out; })
367 #define LDFATAL_FILE(...) ({ load_error(l,f,0,__VA_ARGS__); goto error_out; })
368 #define LDUNSUP_FILE(...) ({ load_error(l,f,1,__VA_ARGS__); goto error_out; })
369 #define KEYFILE_GET(is) ({ \
370 uint##is##_t keyfile_get_tmp=keyfile_get_##is(l,f); \
371 if (!l->postreadcheck(l,f)) goto error_out; \
375 static uint32_t keyfile_get_32(struct load_ctx *l, FILE *f)
385 static uint16_t keyfile_get_16(struct load_ctx *l, FILE *f)
393 static void rsapriv_dispose(void *sst)
395 struct rsapriv *st=sst;
397 mpz_clear(&st->p); mpz_clear(&st->dp);
398 mpz_clear(&st->q); mpz_clear(&st->dq);
400 rsacommon_dispose(&st->common);
404 static struct rsapriv *rsa_loadpriv_core(struct load_ctx *l,
405 FILE *f, struct cloc loc,
406 bool_t do_validity_check)
408 struct rsapriv *st=0;
412 MP_INT e,d,iqmp,tmp,tmp2,tmp3;
423 st->cl.description="rsapriv";
424 st->cl.type=CL_SIGPRIVKEY;
426 st->cl.interface=&st->ops;
428 st->ops.sethash=rsa_priv_sethash;
429 st->common.hashbuf=NULL;
430 st->ops.sign=rsa_sign;
432 st->ops.dispose=rsapriv_dispose;
442 assert(just_check_config);
446 /* Check that the ID string is correct */
447 length=strlen(AUTHFILE_ID_STRING)+1;
448 b=safe_malloc(length,"rsapriv_apply");
449 if (fread(b,length,1,f)!=1 || memcmp(b,AUTHFILE_ID_STRING,length)!=0) {
450 LDUNSUP_FILE("failed to read magic ID"
451 " string from SSH1 private keyfile\n");
455 cipher_type=fgetc(f);
456 KEYFILE_GET(32); /* "Reserved data" */
457 if (cipher_type != 0) {
458 LDUNSUP("we don't support encrypted keyfiles\n");
461 /* Read the public key */
462 KEYFILE_GET(32); /* Not sure what this is */
463 length=(KEYFILE_GET(16)+7)/8;
464 if (length>RSA_MAX_MODBYTES) {
465 LDFATAL("implausible length %ld for modulus\n",
468 b=safe_malloc(length,"rsapriv_apply");
469 if (fread(b,length,1,f) != 1) {
470 LDFATAL_FILE("error reading modulus\n");
472 read_mpbin(&st->n,b,length);
474 length=(KEYFILE_GET(16)+7)/8;
475 if (length>RSA_MAX_MODBYTES) {
476 LDFATAL("implausible length %ld for e\n",length);
478 b=safe_malloc(length,"rsapriv_apply");
479 if (fread(b,length,1,f)!=1) {
480 LDFATAL_FILE("error reading e\n");
482 read_mpbin(&e,b,length);
485 length=KEYFILE_GET(32);
487 LDFATAL("implausibly long (%ld) key comment\n",
490 c=safe_malloc(length+1,"rsapriv_apply");
491 if (fread(c,length,1,f)!=1) {
492 LDFATAL_FILE("error reading key comment\n");
496 /* Check that the next two pairs of characters are identical - the
497 keyfile is not encrypted, so they should be */
499 if (KEYFILE_GET(16) != KEYFILE_GET(16)) {
500 LDFATAL("corrupt keyfile\n");
504 length=(KEYFILE_GET(16)+7)/8;
505 if (length>RSA_MAX_MODBYTES) {
506 LDFATAL("implausibly long (%ld) decryption key\n",
509 b=safe_malloc(length,"rsapriv_apply");
510 if (fread(b,length,1,f)!=1) {
511 LDFATAL_FILE("error reading decryption key\n");
513 read_mpbin(&d,b,length);
515 /* Read iqmp (inverse of q mod p) */
516 length=(KEYFILE_GET(16)+7)/8;
517 if (length>RSA_MAX_MODBYTES) {
518 LDFATAL("implausibly long (%ld)"
519 " iqmp auxiliary value\n", length);
521 b=safe_malloc(length,"rsapriv_apply");
522 if (fread(b,length,1,f)!=1) {
523 LDFATAL_FILE("error reading decryption key\n");
525 read_mpbin(&iqmp,b,length);
527 /* Read q (the smaller of the two primes) */
528 length=(KEYFILE_GET(16)+7)/8;
529 if (length>RSA_MAX_MODBYTES) {
530 LDFATAL("implausibly long (%ld) q value\n",
533 b=safe_malloc(length,"rsapriv_apply");
534 if (fread(b,length,1,f)!=1) {
535 LDFATAL_FILE("error reading q value\n");
537 read_mpbin(&st->q,b,length);
539 /* Read p (the larger of the two primes) */
540 length=(KEYFILE_GET(16)+7)/8;
541 if (length>RSA_MAX_MODBYTES) {
542 LDFATAL("implausibly long (%ld) p value\n",
545 b=safe_malloc(length,"rsapriv_apply");
546 if (fread(b,length,1,f)!=1) {
547 LDFATAL_FILE("error reading p value\n");
549 read_mpbin(&st->p,b,length);
553 fatal_perror("rsa-private (%s:%d): ferror",loc.file,loc.line);
557 * Now verify the validity of the key, and set up the auxiliary
558 * values for fast CRT signing.
561 if (do_validity_check) {
562 /* Verify that p*q is equal to n. */
563 mpz_mul(&tmp, &st->p, &st->q);
564 if (mpz_cmp(&tmp, &st->n) != 0)
568 * Verify that d*e is congruent to 1 mod (p-1), and mod
569 * (q-1). This is equivalent to it being congruent to 1 mod
570 * lambda(n) = lcm(p-1,q-1). The usual `textbook' condition,
571 * that d e == 1 (mod (p-1)(q-1)) is sufficient, but not
572 * actually necessary.
574 mpz_mul(&tmp, &d, &e);
575 mpz_sub_ui(&tmp2, &st->p, 1);
576 mpz_mod(&tmp3, &tmp, &tmp2);
577 if (mpz_cmp_si(&tmp3, 1) != 0)
579 mpz_sub_ui(&tmp2, &st->q, 1);
580 mpz_mod(&tmp3, &tmp, &tmp2);
581 if (mpz_cmp_si(&tmp3, 1) != 0)
584 /* Verify that q*iqmp is congruent to 1 mod p. */
585 mpz_mul(&tmp, &st->q, &iqmp);
586 mpz_mod(&tmp2, &tmp, &st->p);
587 if (mpz_cmp_si(&tmp2, 1) != 0)
590 /* Now we know the key is valid (or we don't care). */
594 * Now we compute auxiliary values dp, dq and w to allow us
595 * to use the CRT optimisation when signing.
597 * dp == d mod (p-1) so that a^dp == a^d mod p, for all a
598 * dq == d mod (q-1) similarly mod q
599 * w == iqmp * q so that w == 0 mod q, and w == 1 mod p
601 mpz_sub_ui(&tmp, &st->p, 1);
602 mpz_mod(&st->dp, &d, &tmp);
603 mpz_sub_ui(&tmp, &st->q, 1);
604 mpz_mod(&st->dq, &d, &tmp);
605 mpz_mul(&st->w, &iqmp, &st->q);
609 LDFATAL("file does not contain a "
628 if (st) rsapriv_dispose(st);
633 static bool_t postreadcheck_tryload(struct load_ctx *l, FILE *f)
636 if (feof(f)) { load_error(l,0,0,"eof mid-integer"); return False; }
640 bool_t rsa1_loadpriv(const struct sigscheme_info *algo,
641 struct buffer_if *privkeydata,
642 struct sigprivkey_if **sigpriv_r,
643 struct log_if *log, struct cloc loc)
646 struct rsapriv *st=0;
648 f=fmemopen(privkeydata->start,privkeydata->size,"r");
650 slilog(log,M_ERR,"failed to fmemopen private key file\n");
654 struct load_ctx l[1];
655 l->what="rsa1priv load";
656 l->verror=verror_tryload;
657 l->postreadcheck=postreadcheck_tryload;
659 l->u.tryload.log=log;
661 st=rsa_loadpriv_core(l,f,loc,False);
662 if (!st) goto error_out;
666 if (st) { free(st); st=0; }
669 if (!st) return False;
674 static bool_t postreadcheck_apply(struct load_ctx *l, FILE *f)
676 cfgfile_postreadcheck(*l->loc,f);
680 static list_t *rsapriv_apply(closure_t *self, struct cloc loc, dict_t *context,
687 struct load_ctx l[1];
689 l->what="rsa-private";
690 l->verror=verror_cfgfatal;
691 l->postreadcheck=postreadcheck_apply;
694 /* Argument is filename pointing to SSH1 private key file */
697 if (i->type!=t_string) {
698 cfgfatal(i->loc,"rsa-private","first argument must be a string\n");
700 filename=i->data.string;
702 filename=NULL; /* Make compiler happy */
703 cfgfatal(i->loc,"rsa-private","you must provide a filename\n");
706 f=fopen(filename,"rb");
708 if (just_check_config) {
709 Message(M_WARNING,"rsa-private (%s:%d): cannot open keyfile "
710 "\"%s\"; assuming it's valid while we check the "
711 "rest of the configuration\n",loc.file,loc.line,filename);
713 fatal_perror("rsa-private (%s:%d): cannot open file \"%s\"",
714 loc.file,loc.line,filename);
718 bool_t do_validity_check=True;
720 if (i && i->type==t_bool && i->data.bool==False) {
721 Message(M_INFO,"rsa-private (%s:%d): skipping RSA key validity "
722 "check\n",loc.file,loc.line);
723 do_validity_check=False;
726 st=rsa_loadpriv_core(l,f,loc,do_validity_check);
728 return new_closure(&st->cl);
731 void rsa_module(dict_t *dict)
733 add_closure(dict,"rsa-private",rsapriv_apply);
734 add_closure(dict,"rsa-public",rsapub_apply);