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.
39 #define AUTHFILE_ID_STRING "SSH PRIVATE KEY FILE FORMAT 1.1\n"
41 #define mpp(s,n) do { char *p = mpz_get_str(NULL,16,n); printf("%s 0x%sL\n", s, p); free(p); } while (0)
45 struct rsaprivkey_if ops
;
54 struct rsapubkey_if ops
;
59 /* Sign data. NB data must be smaller than modulus */
61 #define RSA_MAX_MODBYTES 2048
62 /* The largest modulus I've seen is 15360 bits, which works out at 1920
63 * bytes. Using keys this big is quite implausible, but it doesn't cost us
64 * much to support them.
67 static const char *hexchars
="0123456789abcdef";
69 static void emsa_pkcs1(MP_INT
*n
, MP_INT
*m
,
70 const uint8_t *data
, int32_t datalen
)
72 char buff
[2*RSA_MAX_MODBYTES
+ 1];
75 /* RSA PKCS#1 v1.5 signature padding:
77 * <------------ msize hex digits ---------->
79 * 00 01 ff ff .... ff ff 00 vv vv vv .... vv
83 * = datalen*2 hex digits
85 * NB that according to PKCS#1 v1.5 we're supposed to include a
86 * hash function OID in the data. We don't do that (because we
87 * don't have the hash function OID to hand here), thus violating
88 * the spec in a way that affects interop but not security.
93 msize
=mpz_sizeinbase(n
, 16);
95 if (datalen
*2+6>=msize
) {
96 fatal("rsa_sign: message too big");
101 for (i
=0; i
<datalen
; i
++) {
102 buff
[msize
+(-datalen
+i
)*2]=hexchars
[(data
[i
]&0xf0)>>4];
103 buff
[msize
+(-datalen
+i
)*2+1]=hexchars
[data
[i
]&0xf];
106 buff
[msize
-datalen
*2-2]= '0';
107 buff
[msize
-datalen
*2-1]= '0';
109 for (i
=4; i
<msize
-datalen
*2-2; i
++)
114 mpz_set_str(m
, buff
, 16);
117 static string_t
rsa_sign(void *sst
, uint8_t *data
, int32_t datalen
)
119 struct rsapriv
*st
=sst
;
120 MP_INT a
, b
, u
, v
, tmp
, tmp2
;
126 /* Construct the message representative. */
127 emsa_pkcs1(&st
->n
, &a
, data
, datalen
);
130 * Produce an RSA signature (a^d mod n) using the Chinese
131 * Remainder Theorem. We compute:
133 * u = a^dp mod p (== a^d mod p, since dp == d mod (p-1))
134 * v = a^dq mod q (== a^d mod q, similarly)
136 * We also know w == iqmp * q, which has the property that w ==
137 * 0 mod q and w == 1 mod p. So (1-w) has the reverse property
138 * (congruent to 0 mod p and to 1 mod q). Hence we now compute
140 * b = w * u + (1-w) * v
143 * so that b is congruent to a^d both mod p and mod q. Hence b,
144 * reduced mod n, is the required signature.
151 mpz_powm_sec(&u
, &a
, &st
->dp
, &st
->p
);
152 mpz_powm_sec(&v
, &a
, &st
->dq
, &st
->q
);
153 mpz_sub(&tmp
, &u
, &v
);
154 mpz_mul(&tmp2
, &tmp
, &st
->w
);
155 mpz_add(&tmp
, &tmp2
, &v
);
156 mpz_mod(&b
, &tmp
, &st
->n
);
163 signature
=write_mpstring(&b
);
170 static rsa_checksig_fn rsa_sig_check
;
171 static bool_t
rsa_sig_check(void *sst
, uint8_t *data
, int32_t datalen
,
174 struct rsapub
*st
=sst
;
182 emsa_pkcs1(&st
->n
, &a
, data
, datalen
);
184 mpz_set_str(&b
, signature
, 16);
186 mpz_powm(&c
, &b
, &st
->e
, &st
->n
);
188 ok
=(mpz_cmp(&a
, &c
)==0);
197 static list_t
*rsapub_apply(closure_t
*self
, struct cloc loc
, dict_t
*context
,
205 st
->cl
.description
="rsapub";
206 st
->cl
.type
=CL_RSAPUBKEY
;
208 st
->cl
.interface
=&st
->ops
;
210 st
->ops
.check
=rsa_sig_check
;
215 if (i
->type
!=t_string
) {
216 cfgfatal(i
->loc
,"rsa-public","first argument must be a string\n");
219 if (mpz_init_set_str(&st
->e
,e
,10)!=0) {
220 cfgfatal(i
->loc
,"rsa-public","encryption key \"%s\" is not a "
221 "decimal number string\n",e
);
224 cfgfatal(loc
,"rsa-public","you must provide an encryption key\n");
226 if (mpz_sizeinbase(&st
->e
, 256) > RSA_MAX_MODBYTES
) {
227 cfgfatal(loc
, "rsa-public", "implausibly large public exponent\n");
232 if (i
->type
!=t_string
) {
233 cfgfatal(i
->loc
,"rsa-public","second argument must be a string\n");
236 if (mpz_init_set_str(&st
->n
,n
,10)!=0) {
237 cfgfatal(i
->loc
,"rsa-public","modulus \"%s\" is not a decimal "
238 "number string\n",n
);
241 cfgfatal(loc
,"rsa-public","you must provide a modulus\n");
243 if (mpz_sizeinbase(&st
->n
, 256) > RSA_MAX_MODBYTES
) {
244 cfgfatal(loc
, "rsa-public", "implausibly large modulus\n");
246 return new_closure(&st
->cl
);
249 static uint32_t keyfile_get_int(struct cloc loc
, FILE *f
)
256 cfgfile_postreadcheck(loc
,f
);
260 static uint16_t keyfile_get_short(struct cloc loc
, FILE *f
)
265 cfgfile_postreadcheck(loc
,f
);
269 static list_t
*rsapriv_apply(closure_t
*self
, struct cloc loc
, dict_t
*context
,
279 MP_INT e
,d
,iqmp
,tmp
,tmp2
,tmp3
;
283 st
->cl
.description
="rsapriv";
284 st
->cl
.type
=CL_RSAPRIVKEY
;
286 st
->cl
.interface
=&st
->ops
;
288 st
->ops
.sign
=rsa_sign
;
291 /* Argument is filename pointing to SSH1 private key file */
294 if (i
->type
!=t_string
) {
295 cfgfatal(i
->loc
,"rsa-public","first argument must be a string\n");
297 filename
=i
->data
.string
;
299 filename
=NULL
; /* Make compiler happy */
300 cfgfatal(loc
,"rsa-private","you must provide a filename\n");
303 f
=fopen(filename
,"rb");
305 if (just_check_config
) {
306 Message(M_WARNING
,"rsa-private (%s:%d): cannot open keyfile "
307 "\"%s\"; assuming it's valid while we check the "
308 "rest of the configuration\n",loc
.file
,loc
.line
,filename
);
311 fatal_perror("rsa-private (%s:%d): cannot open file \"%s\"",
312 loc
.file
,loc
.line
,filename
);
316 /* Check that the ID string is correct */
317 length
=strlen(AUTHFILE_ID_STRING
)+1;
318 b
=safe_malloc(length
,"rsapriv_apply");
319 if (fread(b
,length
,1,f
)!=1 || memcmp(b
,AUTHFILE_ID_STRING
,length
)!=0) {
320 cfgfatal_maybefile(f
,loc
,"rsa-private","failed to read magic ID"
321 " string from SSH1 private keyfile \"%s\"\n",
326 cipher_type
=fgetc(f
);
327 keyfile_get_int(loc
,f
); /* "Reserved data" */
328 if (cipher_type
!= 0) {
329 cfgfatal(loc
,"rsa-private","we don't support encrypted keyfiles\n");
332 /* Read the public key */
333 keyfile_get_int(loc
,f
); /* Not sure what this is */
334 length
=(keyfile_get_short(loc
,f
)+7)/8;
335 if (length
>RSA_MAX_MODBYTES
) {
336 cfgfatal(loc
,"rsa-private","implausible length %ld for modulus\n",
339 b
=safe_malloc(length
,"rsapriv_apply");
340 if (fread(b
,length
,1,f
) != 1) {
341 cfgfatal_maybefile(f
,loc
,"rsa-private","error reading modulus\n");
344 read_mpbin(&st
->n
,b
,length
);
346 length
=(keyfile_get_short(loc
,f
)+7)/8;
347 if (length
>RSA_MAX_MODBYTES
) {
348 cfgfatal(loc
,"rsa-private","implausible length %ld for e\n",length
);
350 b
=safe_malloc(length
,"rsapriv_apply");
351 if (fread(b
,length
,1,f
)!=1) {
352 cfgfatal_maybefile(f
,loc
,"rsa-private","error reading e\n");
355 read_mpbin(&e
,b
,length
);
358 length
=keyfile_get_int(loc
,f
);
360 cfgfatal(loc
,"rsa-private","implausibly long (%ld) key comment\n",
363 c
=safe_malloc(length
+1,"rsapriv_apply");
364 if (fread(c
,length
,1,f
)!=1) {
365 cfgfatal_maybefile(f
,loc
,"rsa-private","error reading key comment\n");
369 /* Check that the next two pairs of characters are identical - the
370 keyfile is not encrypted, so they should be */
372 if (keyfile_get_short(loc
,f
) != keyfile_get_short(loc
,f
)) {
373 cfgfatal(loc
,"rsa-private","corrupt keyfile\n");
377 length
=(keyfile_get_short(loc
,f
)+7)/8;
378 if (length
>RSA_MAX_MODBYTES
) {
379 cfgfatal(loc
,"rsa-private","implausibly long (%ld) decryption key\n",
382 b
=safe_malloc(length
,"rsapriv_apply");
383 if (fread(b
,length
,1,f
)!=1) {
384 cfgfatal_maybefile(f
,loc
,"rsa-private",
385 "error reading decryption key\n");
388 read_mpbin(&d
,b
,length
);
390 /* Read iqmp (inverse of q mod p) */
391 length
=(keyfile_get_short(loc
,f
)+7)/8;
392 if (length
>RSA_MAX_MODBYTES
) {
393 cfgfatal(loc
,"rsa-private","implausibly long (%ld)"
394 " iqmp auxiliary value\n", length
);
396 b
=safe_malloc(length
,"rsapriv_apply");
397 if (fread(b
,length
,1,f
)!=1) {
398 cfgfatal_maybefile(f
,loc
,"rsa-private",
399 "error reading decryption key\n");
402 read_mpbin(&iqmp
,b
,length
);
404 /* Read q (the smaller of the two primes) */
405 length
=(keyfile_get_short(loc
,f
)+7)/8;
406 if (length
>RSA_MAX_MODBYTES
) {
407 cfgfatal(loc
,"rsa-private","implausibly long (%ld) q value\n",
410 b
=safe_malloc(length
,"rsapriv_apply");
411 if (fread(b
,length
,1,f
)!=1) {
412 cfgfatal_maybefile(f
,loc
,"rsa-private",
413 "error reading q value\n");
416 read_mpbin(&st
->q
,b
,length
);
418 /* Read p (the larger of the two primes) */
419 length
=(keyfile_get_short(loc
,f
)+7)/8;
420 if (length
>RSA_MAX_MODBYTES
) {
421 cfgfatal(loc
,"rsa-private","implausibly long (%ld) p value\n",
424 b
=safe_malloc(length
,"rsapriv_apply");
425 if (fread(b
,length
,1,f
)!=1) {
426 cfgfatal_maybefile(f
,loc
,"rsa-private",
427 "error reading p value\n");
430 read_mpbin(&st
->p
,b
,length
);
434 fatal_perror("rsa-private (%s:%d): fclose",loc
.file
,loc
.line
);
438 * Now verify the validity of the key, and set up the auxiliary
439 * values for fast CRT signing.
446 if (i
&& i
->type
==t_bool
&& i
->data
.bool==False
) {
447 Message(M_INFO
,"rsa-private (%s:%d): skipping RSA key validity "
448 "check\n",loc
.file
,loc
.line
);
450 /* Verify that p*q is equal to n. */
451 mpz_mul(&tmp
, &st
->p
, &st
->q
);
452 if (mpz_cmp(&tmp
, &st
->n
) != 0)
456 * Verify that d*e is congruent to 1 mod (p-1), and mod
457 * (q-1). This is equivalent to it being congruent to 1 mod
458 * lambda(n) = lcm(p-1,q-1). The usual `textbook' condition,
459 * that d e == 1 (mod (p-1)(q-1)) is sufficient, but not
460 * actually necessary.
462 mpz_mul(&tmp
, &d
, &e
);
463 mpz_sub_ui(&tmp2
, &st
->p
, 1);
464 mpz_mod(&tmp3
, &tmp
, &tmp2
);
465 if (mpz_cmp_si(&tmp3
, 1) != 0)
467 mpz_sub_ui(&tmp2
, &st
->q
, 1);
468 mpz_mod(&tmp3
, &tmp
, &tmp2
);
469 if (mpz_cmp_si(&tmp3
, 1) != 0)
472 /* Verify that q*iqmp is congruent to 1 mod p. */
473 mpz_mul(&tmp
, &st
->q
, &iqmp
);
474 mpz_mod(&tmp2
, &tmp
, &st
->p
);
475 if (mpz_cmp_si(&tmp2
, 1) != 0)
478 /* Now we know the key is valid (or we don't care). */
482 * Now we compute auxiliary values dp, dq and w to allow us
483 * to use the CRT optimisation when signing.
485 * dp == d mod (p-1) so that a^dp == a^d mod p, for all a
486 * dq == d mod (q-1) similarly mod q
487 * w == iqmp * q so that w == 0 mod q, and w == 1 mod p
492 mpz_sub_ui(&tmp
, &st
->p
, 1);
493 mpz_mod(&st
->dp
, &d
, &tmp
);
494 mpz_sub_ui(&tmp
, &st
->q
, 1);
495 mpz_mod(&st
->dq
, &d
, &tmp
);
496 mpz_mul(&st
->w
, &iqmp
, &st
->q
);
500 cfgfatal(loc
,"rsa-private","file \"%s\" does not contain a "
501 "valid RSA key!\n",filename
);
513 return new_closure(&st
->cl
);
516 void rsa_module(dict_t
*dict
)
518 add_closure(dict
,"rsa-private",rsapriv_apply
);
519 add_closure(dict
,"rsa-public",rsapub_apply
);