| 1 | /* |
| 2 | * rsa.c: implementation of RSA with PKCS#1 padding |
| 3 | */ |
| 4 | /* |
| 5 | * This file is Free Software. It was originally written for secnet. |
| 6 | * |
| 7 | * Copyright 1995-2003 Stephen Early |
| 8 | * Copyright 2002-2014 Ian Jackson |
| 9 | * Copyright 2001 Simon Tatham |
| 10 | * Copyright 2013 Mark Wooding |
| 11 | * |
| 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 |
| 15 | * later version. |
| 16 | * |
| 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 |
| 20 | * version. |
| 21 | * |
| 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. |
| 26 | * |
| 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. |
| 30 | */ |
| 31 | |
| 32 | |
| 33 | #include <stdio.h> |
| 34 | #include <string.h> |
| 35 | #include <gmp.h> |
| 36 | #include "secnet.h" |
| 37 | #include "util.h" |
| 38 | |
| 39 | #define AUTHFILE_ID_STRING "SSH PRIVATE KEY FILE FORMAT 1.1\n" |
| 40 | |
| 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) |
| 42 | |
| 43 | struct rsapriv { |
| 44 | closure_t cl; |
| 45 | struct rsaprivkey_if ops; |
| 46 | struct cloc loc; |
| 47 | MP_INT n; |
| 48 | MP_INT p, dp; |
| 49 | MP_INT q, dq; |
| 50 | MP_INT w; |
| 51 | }; |
| 52 | struct rsapub { |
| 53 | closure_t cl; |
| 54 | struct rsapubkey_if ops; |
| 55 | struct cloc loc; |
| 56 | MP_INT e; |
| 57 | MP_INT n; |
| 58 | }; |
| 59 | /* Sign data. NB data must be smaller than modulus */ |
| 60 | |
| 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. |
| 65 | */ |
| 66 | |
| 67 | static const char *hexchars="0123456789abcdef"; |
| 68 | |
| 69 | static void emsa_pkcs1(MP_INT *n, MP_INT *m, |
| 70 | const uint8_t *data, int32_t datalen) |
| 71 | { |
| 72 | char buff[2*RSA_MAX_MODBYTES + 1]; |
| 73 | int msize, i; |
| 74 | |
| 75 | /* RSA PKCS#1 v1.5 signature padding: |
| 76 | * |
| 77 | * <------------ msize hex digits ----------> |
| 78 | * |
| 79 | * 00 01 ff ff .... ff ff 00 vv vv vv .... vv |
| 80 | * |
| 81 | * <--- datalen --> |
| 82 | * bytes |
| 83 | * = datalen*2 hex digits |
| 84 | * |
| 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. |
| 89 | * |
| 90 | * -iwj 17.9.2002 |
| 91 | */ |
| 92 | |
| 93 | msize=mpz_sizeinbase(n, 16); |
| 94 | |
| 95 | if (datalen*2+6>=msize) { |
| 96 | fatal("rsa_sign: message too big"); |
| 97 | } |
| 98 | |
| 99 | strcpy(buff,"0001"); |
| 100 | |
| 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]; |
| 104 | } |
| 105 | |
| 106 | buff[msize-datalen*2-2]= '0'; |
| 107 | buff[msize-datalen*2-1]= '0'; |
| 108 | |
| 109 | for (i=4; i<msize-datalen*2-2; i++) |
| 110 | buff[i]='f'; |
| 111 | |
| 112 | buff[msize]=0; |
| 113 | |
| 114 | mpz_set_str(m, buff, 16); |
| 115 | } |
| 116 | |
| 117 | static string_t rsa_sign(void *sst, uint8_t *data, int32_t datalen) |
| 118 | { |
| 119 | struct rsapriv *st=sst; |
| 120 | MP_INT a, b, u, v, tmp, tmp2; |
| 121 | string_t signature; |
| 122 | |
| 123 | mpz_init(&a); |
| 124 | mpz_init(&b); |
| 125 | |
| 126 | /* Construct the message representative. */ |
| 127 | emsa_pkcs1(&st->n, &a, data, datalen); |
| 128 | |
| 129 | /* |
| 130 | * Produce an RSA signature (a^d mod n) using the Chinese |
| 131 | * Remainder Theorem. We compute: |
| 132 | * |
| 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) |
| 135 | * |
| 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 |
| 139 | * |
| 140 | * b = w * u + (1-w) * v |
| 141 | * = w * (u-v) + v |
| 142 | * |
| 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. |
| 145 | */ |
| 146 | mpz_init(&tmp); |
| 147 | mpz_init(&tmp2); |
| 148 | mpz_init(&u); |
| 149 | mpz_init(&v); |
| 150 | |
| 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); |
| 157 | |
| 158 | mpz_clear(&tmp); |
| 159 | mpz_clear(&tmp2); |
| 160 | mpz_clear(&u); |
| 161 | mpz_clear(&v); |
| 162 | |
| 163 | signature=write_mpstring(&b); |
| 164 | |
| 165 | mpz_clear(&b); |
| 166 | mpz_clear(&a); |
| 167 | return signature; |
| 168 | } |
| 169 | |
| 170 | static rsa_checksig_fn rsa_sig_check; |
| 171 | static bool_t rsa_sig_check(void *sst, uint8_t *data, int32_t datalen, |
| 172 | cstring_t signature) |
| 173 | { |
| 174 | struct rsapub *st=sst; |
| 175 | MP_INT a, b, c; |
| 176 | bool_t ok; |
| 177 | |
| 178 | mpz_init(&a); |
| 179 | mpz_init(&b); |
| 180 | mpz_init(&c); |
| 181 | |
| 182 | emsa_pkcs1(&st->n, &a, data, datalen); |
| 183 | |
| 184 | mpz_set_str(&b, signature, 16); |
| 185 | |
| 186 | mpz_powm(&c, &b, &st->e, &st->n); |
| 187 | |
| 188 | ok=(mpz_cmp(&a, &c)==0); |
| 189 | |
| 190 | mpz_clear(&c); |
| 191 | mpz_clear(&b); |
| 192 | mpz_clear(&a); |
| 193 | |
| 194 | return ok; |
| 195 | } |
| 196 | |
| 197 | static list_t *rsapub_apply(closure_t *self, struct cloc loc, dict_t *context, |
| 198 | list_t *args) |
| 199 | { |
| 200 | struct rsapub *st; |
| 201 | item_t *i; |
| 202 | string_t e,n; |
| 203 | |
| 204 | NEW(st); |
| 205 | st->cl.description="rsapub"; |
| 206 | st->cl.type=CL_RSAPUBKEY; |
| 207 | st->cl.apply=NULL; |
| 208 | st->cl.interface=&st->ops; |
| 209 | st->ops.st=st; |
| 210 | st->ops.check=rsa_sig_check; |
| 211 | st->loc=loc; |
| 212 | |
| 213 | i=list_elem(args,0); |
| 214 | if (i) { |
| 215 | if (i->type!=t_string) { |
| 216 | cfgfatal(i->loc,"rsa-public","first argument must be a string\n"); |
| 217 | } |
| 218 | e=i->data.string; |
| 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); |
| 222 | } |
| 223 | } else { |
| 224 | cfgfatal(loc,"rsa-public","you must provide an encryption key\n"); |
| 225 | } |
| 226 | if (mpz_sizeinbase(&st->e, 256) > RSA_MAX_MODBYTES) { |
| 227 | cfgfatal(loc, "rsa-public", "implausibly large public exponent\n"); |
| 228 | } |
| 229 | |
| 230 | i=list_elem(args,1); |
| 231 | if (i) { |
| 232 | if (i->type!=t_string) { |
| 233 | cfgfatal(i->loc,"rsa-public","second argument must be a string\n"); |
| 234 | } |
| 235 | n=i->data.string; |
| 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); |
| 239 | } |
| 240 | } else { |
| 241 | cfgfatal(loc,"rsa-public","you must provide a modulus\n"); |
| 242 | } |
| 243 | if (mpz_sizeinbase(&st->n, 256) > RSA_MAX_MODBYTES) { |
| 244 | cfgfatal(loc, "rsa-public", "implausibly large modulus\n"); |
| 245 | } |
| 246 | return new_closure(&st->cl); |
| 247 | } |
| 248 | |
| 249 | static uint32_t keyfile_get_int(struct cloc loc, FILE *f) |
| 250 | { |
| 251 | uint32_t r; |
| 252 | r=fgetc(f)<<24; |
| 253 | r|=fgetc(f)<<16; |
| 254 | r|=fgetc(f)<<8; |
| 255 | r|=fgetc(f); |
| 256 | cfgfile_postreadcheck(loc,f); |
| 257 | return r; |
| 258 | } |
| 259 | |
| 260 | static uint16_t keyfile_get_short(struct cloc loc, FILE *f) |
| 261 | { |
| 262 | uint16_t r; |
| 263 | r=fgetc(f)<<8; |
| 264 | r|=fgetc(f); |
| 265 | cfgfile_postreadcheck(loc,f); |
| 266 | return r; |
| 267 | } |
| 268 | |
| 269 | static list_t *rsapriv_apply(closure_t *self, struct cloc loc, dict_t *context, |
| 270 | list_t *args) |
| 271 | { |
| 272 | struct rsapriv *st; |
| 273 | FILE *f; |
| 274 | cstring_t filename; |
| 275 | item_t *i; |
| 276 | long length; |
| 277 | uint8_t *b, *c; |
| 278 | int cipher_type; |
| 279 | MP_INT e,d,iqmp,tmp,tmp2,tmp3; |
| 280 | bool_t valid; |
| 281 | |
| 282 | NEW(st); |
| 283 | st->cl.description="rsapriv"; |
| 284 | st->cl.type=CL_RSAPRIVKEY; |
| 285 | st->cl.apply=NULL; |
| 286 | st->cl.interface=&st->ops; |
| 287 | st->ops.st=st; |
| 288 | st->ops.sign=rsa_sign; |
| 289 | st->loc=loc; |
| 290 | |
| 291 | /* Argument is filename pointing to SSH1 private key file */ |
| 292 | i=list_elem(args,0); |
| 293 | if (i) { |
| 294 | if (i->type!=t_string) { |
| 295 | cfgfatal(i->loc,"rsa-private","first argument must be a string\n"); |
| 296 | } |
| 297 | filename=i->data.string; |
| 298 | } else { |
| 299 | filename=NULL; /* Make compiler happy */ |
| 300 | cfgfatal(loc,"rsa-private","you must provide a filename\n"); |
| 301 | } |
| 302 | |
| 303 | f=fopen(filename,"rb"); |
| 304 | if (!f) { |
| 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); |
| 309 | goto assume_valid; |
| 310 | } else { |
| 311 | fatal_perror("rsa-private (%s:%d): cannot open file \"%s\"", |
| 312 | loc.file,loc.line,filename); |
| 313 | } |
| 314 | } |
| 315 | |
| 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", |
| 322 | filename); |
| 323 | } |
| 324 | free(b); |
| 325 | |
| 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"); |
| 330 | } |
| 331 | |
| 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", |
| 337 | length); |
| 338 | } |
| 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"); |
| 342 | } |
| 343 | mpz_init(&st->n); |
| 344 | read_mpbin(&st->n,b,length); |
| 345 | free(b); |
| 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); |
| 349 | } |
| 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"); |
| 353 | } |
| 354 | mpz_init(&e); |
| 355 | read_mpbin(&e,b,length); |
| 356 | free(b); |
| 357 | |
| 358 | length=keyfile_get_int(loc,f); |
| 359 | if (length>1024) { |
| 360 | cfgfatal(loc,"rsa-private","implausibly long (%ld) key comment\n", |
| 361 | length); |
| 362 | } |
| 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"); |
| 366 | } |
| 367 | c[length]=0; |
| 368 | |
| 369 | /* Check that the next two pairs of characters are identical - the |
| 370 | keyfile is not encrypted, so they should be */ |
| 371 | |
| 372 | if (keyfile_get_short(loc,f) != keyfile_get_short(loc,f)) { |
| 373 | cfgfatal(loc,"rsa-private","corrupt keyfile\n"); |
| 374 | } |
| 375 | |
| 376 | /* Read d */ |
| 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", |
| 380 | length); |
| 381 | } |
| 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"); |
| 386 | } |
| 387 | mpz_init(&d); |
| 388 | read_mpbin(&d,b,length); |
| 389 | free(b); |
| 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); |
| 395 | } |
| 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"); |
| 400 | } |
| 401 | mpz_init(&iqmp); |
| 402 | read_mpbin(&iqmp,b,length); |
| 403 | free(b); |
| 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", |
| 408 | length); |
| 409 | } |
| 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"); |
| 414 | } |
| 415 | mpz_init(&st->q); |
| 416 | read_mpbin(&st->q,b,length); |
| 417 | free(b); |
| 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", |
| 422 | length); |
| 423 | } |
| 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"); |
| 428 | } |
| 429 | mpz_init(&st->p); |
| 430 | read_mpbin(&st->p,b,length); |
| 431 | free(b); |
| 432 | |
| 433 | if (fclose(f)!=0) { |
| 434 | fatal_perror("rsa-private (%s:%d): fclose",loc.file,loc.line); |
| 435 | } |
| 436 | |
| 437 | /* |
| 438 | * Now verify the validity of the key, and set up the auxiliary |
| 439 | * values for fast CRT signing. |
| 440 | */ |
| 441 | valid=False; |
| 442 | i=list_elem(args,1); |
| 443 | mpz_init(&tmp); |
| 444 | mpz_init(&tmp2); |
| 445 | mpz_init(&tmp3); |
| 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); |
| 449 | } else { |
| 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) |
| 453 | goto done_checks; |
| 454 | |
| 455 | /* |
| 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. |
| 461 | */ |
| 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) |
| 466 | goto done_checks; |
| 467 | mpz_sub_ui(&tmp2, &st->q, 1); |
| 468 | mpz_mod(&tmp3, &tmp, &tmp2); |
| 469 | if (mpz_cmp_si(&tmp3, 1) != 0) |
| 470 | goto done_checks; |
| 471 | |
| 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) |
| 476 | goto done_checks; |
| 477 | } |
| 478 | /* Now we know the key is valid (or we don't care). */ |
| 479 | valid = True; |
| 480 | |
| 481 | /* |
| 482 | * Now we compute auxiliary values dp, dq and w to allow us |
| 483 | * to use the CRT optimisation when signing. |
| 484 | * |
| 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 |
| 488 | */ |
| 489 | mpz_init(&st->dp); |
| 490 | mpz_init(&st->dq); |
| 491 | mpz_init(&st->w); |
| 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); |
| 497 | |
| 498 | done_checks: |
| 499 | if (!valid) { |
| 500 | cfgfatal(loc,"rsa-private","file \"%s\" does not contain a " |
| 501 | "valid RSA key!\n",filename); |
| 502 | } |
| 503 | mpz_clear(&tmp); |
| 504 | mpz_clear(&tmp2); |
| 505 | mpz_clear(&tmp3); |
| 506 | |
| 507 | free(c); |
| 508 | mpz_clear(&e); |
| 509 | mpz_clear(&d); |
| 510 | mpz_clear(&iqmp); |
| 511 | |
| 512 | assume_valid: |
| 513 | return new_closure(&st->cl); |
| 514 | } |
| 515 | |
| 516 | void rsa_module(dict_t *dict) |
| 517 | { |
| 518 | add_closure(dict,"rsa-private",rsapriv_apply); |
| 519 | add_closure(dict,"rsa-public",rsapub_apply); |
| 520 | } |