mdw@git.distorted.org.uk Git - secnet/blob - rsa.c

   1 /* This file is part of secnet, and is distributed under the terms of
   2    the GNU General Public License version 2 or later.
   3
   4    Copyright (C) 1995-2002 Stephen Early
   5    Copyright (C) 2001 Simon Tatham
   6    Copyright (C) 2002 Ian Jackson
   7    */
   8
   9 #include <stdio.h>
  10 #include <string.h>
  11 #include <gmp.h>
  12 #include "secnet.h"
  13 #include "util.h"
  14
  15 #define AUTHFILE_ID_STRING "SSH PRIVATE KEY FILE FORMAT 1.1\n"
  16
  17 #define mpp(s,n) do { char *p = mpz_get_str(NULL,16,n); printf("%s 0x%sL\n", s, p); free(p); } while (0)
  18
  19 struct rsapriv {
  20     closure_t cl;
  21     struct rsaprivkey_if ops;
  22     struct cloc loc;
  23     MP_INT n;
  24     MP_INT p, dp;
  25     MP_INT q, dq;
  26     MP_INT w;
  27 };
  28 struct rsapub {
  29     closure_t cl;
  30     struct rsapubkey_if ops;
  31     struct cloc loc;
  32     MP_INT e;
  33     MP_INT n;
  34 };
  35 /* Sign data. NB data must be smaller than modulus */
  36
  37 #define RSA_MAX_MODBYTES 2048
  38 /* The largest modulus I've seen is 15360 bits, which works out at 1920
  39  * bytes.  Using keys this big is quite implausible, but it doesn't cost us
  40  * much to support them.
  41  */
  42
  43 static const char *hexchars="0123456789abcdef";
  44
  45 static void emsa_pkcs1(MP_INT *n, MP_INT *m,
  46                        const uint8_t *data, int32_t datalen)
  47 {
  48     char buff[2*RSA_MAX_MODBYTES + 1];
  49     int msize, i;
  50
  51     /* RSA PKCS#1 v1.5 signature padding:
  52      *
  53      * <------------ msize hex digits ---------->
  54      *
  55      * 00 01 ff ff .... ff ff 00 vv vv vv .... vv
  56      *
  57      *                           <--- datalen -->
  58      *                                 bytes
  59      *                         = datalen*2 hex digits
  60      *
  61      * NB that according to PKCS#1 v1.5 we're supposed to include a
  62      * hash function OID in the data.  We don't do that (because we
  63      * don't have the hash function OID to hand here), thus violating
  64      * the spec in a way that affects interop but not security.
  65      *
  66      * -iwj 17.9.2002
  67      */
  68
  69     msize=mpz_sizeinbase(n, 16);
  70
  71     if (datalen*2+6>=msize) {
  72         fatal("rsa_sign: message too big");
  73     }
  74
  75     strcpy(buff,"0001");
  76
  77     for (i=0; i<datalen; i++) {
  78         buff[msize+(-datalen+i)*2]=hexchars[(data[i]&0xf0)>>4];
  79         buff[msize+(-datalen+i)*2+1]=hexchars[data[i]&0xf];
  80     }
  81
  82     buff[msize-datalen*2-2]= '0';
  83     buff[msize-datalen*2-1]= '0';
  84
  85     for (i=4; i<msize-datalen*2-2; i++)
  86        buff[i]='f';
  87
  88     buff[msize]=0;
  89
  90     mpz_set_str(m, buff, 16);
  91 }
  92
  93 static string_t rsa_sign(void *sst, uint8_t *data, int32_t datalen)
  94 {
  95     struct rsapriv *st=sst;
  96     MP_INT a, b, u, v, tmp, tmp2;
  97     string_t signature;
  98
  99     mpz_init(&a);
 100     mpz_init(&b);
 101
 102     /* Construct the message representative. */
 103     emsa_pkcs1(&st->n, &a, data, datalen);
 104
 105     /*
 106      * Produce an RSA signature (a^d mod n) using the Chinese
 107      * Remainder Theorem. We compute:
 108      *
 109      *   u = a^dp mod p    (== a^d mod p, since dp == d mod (p-1))
 110      *   v = a^dq mod q    (== a^d mod q, similarly)
 111      *
 112      * We also know w == iqmp * q, which has the property that w ==
 113      * 0 mod q and w == 1 mod p. So (1-w) has the reverse property
 114      * (congruent to 0 mod p and to 1 mod q). Hence we now compute
 115      *
 116      *   b = w * u + (1-w) * v
 117      *     = w * (u-v) + v
 118      *
 119      * so that b is congruent to a^d both mod p and mod q. Hence b,
 120      * reduced mod n, is the required signature.
 121      */
 122     mpz_init(&tmp);
 123     mpz_init(&tmp2);
 124     mpz_init(&u);
 125     mpz_init(&v);
 126
 127     mpz_powm(&u, &a, &st->dp, &st->p);
 128     mpz_powm(&v, &a, &st->dq, &st->q);
 129     mpz_sub(&tmp, &u, &v);
 130     mpz_mul(&tmp2, &tmp, &st->w);
 131     mpz_add(&tmp, &tmp2, &v);
 132     mpz_mod(&b, &tmp, &st->n);
 133
 134     mpz_clear(&tmp);
 135     mpz_clear(&tmp2);
 136     mpz_clear(&u);
 137     mpz_clear(&v);
 138
 139     signature=write_mpstring(&b);
 140
 141     mpz_clear(&b);
 142     mpz_clear(&a);
 143     return signature;
 144 }
 145
 146 static rsa_checksig_fn rsa_sig_check;
 147 static bool_t rsa_sig_check(void *sst, uint8_t *data, int32_t datalen,
 148                             cstring_t signature)
 149 {
 150     struct rsapub *st=sst;
 151     MP_INT a, b, c;
 152     bool_t ok;
 153
 154     mpz_init(&a);
 155     mpz_init(&b);
 156     mpz_init(&c);
 157
 158     emsa_pkcs1(&st->n, &a, data, datalen);
 159
 160     mpz_set_str(&b, signature, 16);
 161
 162     mpz_powm(&c, &b, &st->e, &st->n);
 163
 164     ok=(mpz_cmp(&a, &c)==0);
 165
 166     mpz_clear(&c);
 167     mpz_clear(&b);
 168     mpz_clear(&a);
 169
 170     return ok;
 171 }
 172
 173 static list_t *rsapub_apply(closure_t *self, struct cloc loc, dict_t *context,
 174                             list_t *args)
 175 {
 176     struct rsapub *st;
 177     item_t *i;
 178     string_t e,n;
 179
 180     st=safe_malloc(sizeof(*st),"rsapub_apply");
 181     st->cl.description="rsapub";
 182     st->cl.type=CL_RSAPUBKEY;
 183     st->cl.apply=NULL;
 184     st->cl.interface=&st->ops;
 185     st->ops.st=st;
 186     st->ops.check=rsa_sig_check;
 187     st->loc=loc;
 188
 189     i=list_elem(args,0);
 190     if (i) {
 191         if (i->type!=t_string) {
 192             cfgfatal(i->loc,"rsa-public","first argument must be a string\n");
 193         }
 194         e=i->data.string;
 195         if (mpz_init_set_str(&st->e,e,10)!=0) {
 196             cfgfatal(i->loc,"rsa-public","encryption key \"%s\" is not a "
 197                      "decimal number string\n",e);
 198         }
 199     } else {
 200         cfgfatal(loc,"rsa-public","you must provide an encryption key\n");
 201     }
 202
 203     i=list_elem(args,1);
 204     if (i) {
 205         if (i->type!=t_string) {
 206             cfgfatal(i->loc,"rsa-public","second argument must be a string\n");
 207         }
 208         n=i->data.string;
 209         if (mpz_init_set_str(&st->n,n,10)!=0) {
 210             cfgfatal(i->loc,"rsa-public","modulus \"%s\" is not a decimal "
 211                      "number string\n",n);
 212         }
 213     } else {
 214         cfgfatal(loc,"rsa-public","you must provide a modulus\n");
 215     }
 216     return new_closure(&st->cl);
 217 }
 218
 219 static uint32_t keyfile_get_int(struct cloc loc, FILE *f)
 220 {
 221     uint32_t r;
 222     r=fgetc(f)<<24;
 223     r|=fgetc(f)<<16;
 224     r|=fgetc(f)<<8;
 225     r|=fgetc(f);
 226     cfgfile_postreadcheck(loc,f);
 227     return r;
 228 }
 229
 230 static uint16_t keyfile_get_short(struct cloc loc, FILE *f)
 231 {
 232     uint16_t r;
 233     r=fgetc(f)<<8;
 234     r|=fgetc(f);
 235     cfgfile_postreadcheck(loc,f);
 236     return r;
 237 }
 238
 239 static list_t *rsapriv_apply(closure_t *self, struct cloc loc, dict_t *context,
 240                              list_t *args)
 241 {
 242     struct rsapriv *st;
 243     FILE *f;
 244     cstring_t filename;
 245     item_t *i;
 246     long length;
 247     uint8_t *b, *c;
 248     int cipher_type;
 249     MP_INT e,d,iqmp,tmp,tmp2,tmp3;
 250     bool_t valid;
 251
 252     st=safe_malloc(sizeof(*st),"rsapriv_apply");
 253     st->cl.description="rsapriv";
 254     st->cl.type=CL_RSAPRIVKEY;
 255     st->cl.apply=NULL;
 256     st->cl.interface=&st->ops;
 257     st->ops.st=st;
 258     st->ops.sign=rsa_sign;
 259     st->loc=loc;
 260
 261     /* Argument is filename pointing to SSH1 private key file */
 262     i=list_elem(args,0);
 263     if (i) {
 264         if (i->type!=t_string) {
 265             cfgfatal(i->loc,"rsa-public","first argument must be a string\n");
 266         }
 267         filename=i->data.string;
 268     } else {
 269         filename=NULL; /* Make compiler happy */
 270         cfgfatal(loc,"rsa-private","you must provide a filename\n");
 271     }
 272
 273     f=fopen(filename,"rb");
 274     if (!f) {
 275         if (just_check_config) {
 276             Message(M_WARNING,"rsa-private (%s:%d): cannot open keyfile "
 277                     "\"%s\"; assuming it's valid while we check the "
 278                     "rest of the configuration\n",loc.file,loc.line,filename);
 279             goto assume_valid;
 280         } else {
 281             fatal_perror("rsa-private (%s:%d): cannot open file \"%s\"",
 282                          loc.file,loc.line,filename);
 283         }
 284     }
 285
 286     /* Check that the ID string is correct */
 287     length=strlen(AUTHFILE_ID_STRING)+1;
 288     b=safe_malloc(length,"rsapriv_apply");
 289     if (fread(b,length,1,f)!=1 || memcmp(b,AUTHFILE_ID_STRING,length)!=0) {
 290         cfgfatal_maybefile(f,loc,"rsa-private","failed to read magic ID"
 291                            " string from SSH1 private keyfile \"%s\"\n",
 292                            filename);
 293     }
 294     free(b);
 295
 296     cipher_type=fgetc(f);
 297     keyfile_get_int(loc,f); /* "Reserved data" */
 298     if (cipher_type != 0) {
 299         cfgfatal(loc,"rsa-private","we don't support encrypted keyfiles\n");
 300     }
 301
 302     /* Read the public key */
 303     keyfile_get_int(loc,f); /* Not sure what this is */
 304     length=(keyfile_get_short(loc,f)+7)/8;
 305     if (length>RSA_MAX_MODBYTES) {
 306         cfgfatal(loc,"rsa-private","implausible length %ld for modulus\n",
 307                  length);
 308     }
 309     b=safe_malloc(length,"rsapriv_apply");
 310     if (fread(b,length,1,f) != 1) {
 311         cfgfatal_maybefile(f,loc,"rsa-private","error reading modulus\n");
 312     }
 313     mpz_init(&st->n);
 314     read_mpbin(&st->n,b,length);
 315     free(b);
 316     length=(keyfile_get_short(loc,f)+7)/8;
 317     if (length>RSA_MAX_MODBYTES) {
 318         cfgfatal(loc,"rsa-private","implausible length %ld for e\n",length);
 319     }
 320     b=safe_malloc(length,"rsapriv_apply");
 321     if (fread(b,length,1,f)!=1) {
 322         cfgfatal_maybefile(f,loc,"rsa-private","error reading e\n");
 323     }
 324     mpz_init(&e);
 325     read_mpbin(&e,b,length);
 326     free(b);
 327
 328     length=keyfile_get_int(loc,f);
 329     if (length>1024) {
 330         cfgfatal(loc,"rsa-private","implausibly long (%ld) key comment\n",
 331                  length);
 332     }
 333     c=safe_malloc(length+1,"rsapriv_apply");
 334     if (fread(c,length,1,f)!=1) {
 335         cfgfatal_maybefile(f,loc,"rsa-private","error reading key comment\n");
 336     }
 337     c[length]=0;
 338
 339     /* Check that the next two pairs of characters are identical - the
 340        keyfile is not encrypted, so they should be */
 341
 342     if (keyfile_get_short(loc,f) != keyfile_get_short(loc,f)) {
 343         cfgfatal(loc,"rsa-private","corrupt keyfile\n");
 344     }
 345
 346     /* Read d */
 347     length=(keyfile_get_short(loc,f)+7)/8;
 348     if (length>RSA_MAX_MODBYTES) {
 349         cfgfatal(loc,"rsa-private","implausibly long (%ld) decryption key\n",
 350                  length);
 351     }
 352     b=safe_malloc(length,"rsapriv_apply");
 353     if (fread(b,length,1,f)!=1) {
 354         cfgfatal_maybefile(f,loc,"rsa-private",
 355                            "error reading decryption key\n");
 356     }
 357     mpz_init(&d);
 358     read_mpbin(&d,b,length);
 359     free(b);
 360     /* Read iqmp (inverse of q mod p) */
 361     length=(keyfile_get_short(loc,f)+7)/8;
 362     if (length>RSA_MAX_MODBYTES) {
 363         cfgfatal(loc,"rsa-private","implausibly long (%ld)"
 364                  " iqmp auxiliary value\n", length);
 365     }
 366     b=safe_malloc(length,"rsapriv_apply");
 367     if (fread(b,length,1,f)!=1) {
 368         cfgfatal_maybefile(f,loc,"rsa-private",
 369                            "error reading decryption key\n");
 370     }
 371     mpz_init(&iqmp);
 372     read_mpbin(&iqmp,b,length);
 373     free(b);
 374     /* Read q (the smaller of the two primes) */
 375     length=(keyfile_get_short(loc,f)+7)/8;
 376     if (length>RSA_MAX_MODBYTES) {
 377         cfgfatal(loc,"rsa-private","implausibly long (%ld) q value\n",
 378                  length);
 379     }
 380     b=safe_malloc(length,"rsapriv_apply");
 381     if (fread(b,length,1,f)!=1) {
 382         cfgfatal_maybefile(f,loc,"rsa-private",
 383                            "error reading q value\n");
 384     }
 385     mpz_init(&st->q);
 386     read_mpbin(&st->q,b,length);
 387     free(b);
 388     /* Read p (the larger of the two primes) */
 389     length=(keyfile_get_short(loc,f)+7)/8;
 390     if (length>RSA_MAX_MODBYTES) {
 391         cfgfatal(loc,"rsa-private","implausibly long (%ld) p value\n",
 392                  length);
 393     }
 394     b=safe_malloc(length,"rsapriv_apply");
 395     if (fread(b,length,1,f)!=1) {
 396         cfgfatal_maybefile(f,loc,"rsa-private",
 397                            "error reading p value\n");
 398     }
 399     mpz_init(&st->p);
 400     read_mpbin(&st->p,b,length);
 401     free(b);
 402
 403     if (fclose(f)!=0) {
 404         fatal_perror("rsa-private (%s:%d): fclose",loc.file,loc.line);
 405     }
 406
 407     /*
 408      * Now verify the validity of the key, and set up the auxiliary
 409      * values for fast CRT signing.
 410      */
 411     valid=False;
 412     i=list_elem(args,1);
 413     mpz_init(&tmp);
 414     mpz_init(&tmp2);
 415     mpz_init(&tmp3);
 416     if (i && i->type==t_bool && i->data.bool==False) {
 417         Message(M_INFO,"rsa-private (%s:%d): skipping RSA key validity "
 418                 "check\n",loc.file,loc.line);
 419     } else {
 420         /* Verify that p*q is equal to n. */
 421         mpz_mul(&tmp, &st->p, &st->q);
 422         if (mpz_cmp(&tmp, &st->n) != 0)
 423             goto done_checks;
 424
 425         /*
 426          * Verify that d*e is congruent to 1 mod (p-1), and mod
 427          * (q-1). This is equivalent to it being congruent to 1 mod
 428          * lambda(n) = lcm(p-1,q-1).  The usual `textbook' condition,
 429          * that d e == 1 (mod (p-1)(q-1)) is sufficient, but not
 430          * actually necessary.
 431          */
 432         mpz_mul(&tmp, &d, &e);
 433         mpz_sub_ui(&tmp2, &st->p, 1);
 434         mpz_mod(&tmp3, &tmp, &tmp2);
 435         if (mpz_cmp_si(&tmp3, 1) != 0)
 436             goto done_checks;
 437         mpz_sub_ui(&tmp2, &st->q, 1);
 438         mpz_mod(&tmp3, &tmp, &tmp2);
 439         if (mpz_cmp_si(&tmp3, 1) != 0)
 440             goto done_checks;
 441
 442         /* Verify that q*iqmp is congruent to 1 mod p. */
 443         mpz_mul(&tmp, &st->q, &iqmp);
 444         mpz_mod(&tmp2, &tmp, &st->p);
 445         if (mpz_cmp_si(&tmp2, 1) != 0)
 446             goto done_checks;
 447     }
 448     /* Now we know the key is valid (or we don't care). */
 449     valid = True;
 450
 451     /*
 452      * Now we compute auxiliary values dp, dq and w to allow us
 453      * to use the CRT optimisation when signing.
 454      *
 455      *   dp == d mod (p-1)      so that a^dp == a^d mod p, for all a
 456      *   dq == d mod (q-1)      similarly mod q
 457      *   w == iqmp * q          so that w == 0 mod q, and w == 1 mod p
 458      */
 459     mpz_init(&st->dp);
 460     mpz_init(&st->dq);
 461     mpz_init(&st->w);
 462     mpz_sub_ui(&tmp, &st->p, 1);
 463     mpz_mod(&st->dp, &d, &tmp);
 464     mpz_sub_ui(&tmp, &st->q, 1);
 465     mpz_mod(&st->dq, &d, &tmp);
 466     mpz_mul(&st->w, &iqmp, &st->q);
 467
 468 done_checks:
 469     if (!valid) {
 470         cfgfatal(loc,"rsa-private","file \"%s\" does not contain a "
 471                  "valid RSA key!\n",filename);
 472     }
 473     mpz_clear(&tmp);
 474     mpz_clear(&tmp2);
 475     mpz_clear(&tmp3);
 476
 477     free(c);
 478     mpz_clear(&e);
 479     mpz_clear(&d);
 480     mpz_clear(&iqmp);
 481
 482 assume_valid:
 483     return new_closure(&st->cl);
 484 }
 485
 486 void rsa_module(dict_t *dict)
 487 {
 488     add_closure(dict,"rsa-private",rsapriv_apply);
 489     add_closure(dict,"rsa-public",rsapub_apply);
 490 }