src/lib/crypt_ops/crypto_s2k.c

   1 /* Copyright (c) 2001, Matej Pfajfar.
   2  * Copyright (c) 2001-2004, Roger Dingledine.
   3  * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
   4  * Copyright (c) 2007-2019, The Tor Project, Inc. */
   5 /* See LICENSE for licensing information */
   6
   7 /**
   8  * \file crypto_s2k.c
   9  *
  10  * \brief Functions for deriving keys from human-readable passphrases.
  11  */
  12
  13 #define CRYPTO_S2K_PRIVATE
  14
  15 #include "lib/crypt_ops/crypto_cipher.h"
  16 #include "lib/crypt_ops/crypto_digest.h"
  17 #include "lib/crypt_ops/crypto_hkdf.h"
  18 #include "lib/crypt_ops/crypto_rand.h"
  19 #include "lib/crypt_ops/crypto_s2k.h"
  20 #include "lib/crypt_ops/crypto_util.h"
  21 #include "lib/ctime/di_ops.h"
  22 #include "lib/log/util_bug.h"
  23 #include "lib/intmath/cmp.h"
  24
  25 #ifdef ENABLE_OPENSSL
  26 #include <openssl/evp.h>
  27 #endif
  28 #ifdef ENABLE_NSS
  29 #include <pk11pub.h>
  30 #endif
  31
  32 #if defined(HAVE_LIBSCRYPT_H) && defined(HAVE_LIBSCRYPT_SCRYPT)
  33 #define HAVE_SCRYPT
  34 #include <libscrypt.h>
  35 #endif
  36
  37 #include <string.h>
  38
  39 /* Encoded secrets take the form:
  40
  41      u8 type;
  42      u8 salt_and_parameters[depends on type];
  43      u8 key[depends on type];
  44
  45    As a special case, if the encoded secret is exactly 29 bytes long,
  46    type 0 is understood.
  47
  48    Recognized types are:
  49        00 -- RFC2440. salt_and_parameters is 9 bytes. key is 20 bytes.
  50                 salt_and_parameters is 8 bytes random salt,
  51                 1 byte iteration info.
  52        01 -- PKBDF2_SHA1. salt_and_parameters is 17 bytes. key is 20 bytes.
  53                 salt_and_parameters is 16 bytes random salt,
  54                 1 byte iteration info.
  55        02 -- SCRYPT_SALSA208_SHA256. salt_and_parameters is 18 bytes. key is
  56              32 bytes.
  57                 salt_and_parameters is 18 bytes random salt, 2 bytes iteration
  58                 info.
  59 */
  60
  61 #define S2K_TYPE_RFC2440 0
  62 #define S2K_TYPE_PBKDF2  1
  63 #define S2K_TYPE_SCRYPT  2
  64
  65 #define PBKDF2_SPEC_LEN 17
  66 #define PBKDF2_KEY_LEN 20
  67
  68 #define SCRYPT_SPEC_LEN 18
  69 #define SCRYPT_KEY_LEN 32
  70
  71 /** Given an algorithm ID (one of S2K_TYPE_*), return the length of the
  72  * specifier part of it, without the prefix type byte.  Return -1 if it is not
  73  * a valid algorithm ID. */
  74 static int
  75 secret_to_key_spec_len(uint8_t type)
  76 {
  77   switch (type) {
  78     case S2K_TYPE_RFC2440:
  79       return S2K_RFC2440_SPECIFIER_LEN;
  80     case S2K_TYPE_PBKDF2:
  81       return PBKDF2_SPEC_LEN;
  82     case S2K_TYPE_SCRYPT:
  83       return SCRYPT_SPEC_LEN;
  84     default:
  85       return -1;
  86   }
  87 }
  88
  89 /** Given an algorithm ID (one of S2K_TYPE_*), return the length of the
  90  * its preferred output. */
  91 static int
  92 secret_to_key_key_len(uint8_t type)
  93 {
  94   switch (type) {
  95     case S2K_TYPE_RFC2440:
  96       return DIGEST_LEN;
  97     case S2K_TYPE_PBKDF2:
  98       return DIGEST_LEN;
  99     case S2K_TYPE_SCRYPT:
 100       return DIGEST256_LEN;
 101     // LCOV_EXCL_START
 102     default:
 103       tor_fragile_assert();
 104       return -1;
 105     // LCOV_EXCL_STOP
 106   }
 107 }
 108
 109 /** Given a specifier in <b>spec_and_key</b> of length
 110  * <b>spec_and_key_len</b>, along with its prefix algorithm ID byte, and along
 111  * with a key if <b>key_included</b> is true, check whether the whole
 112  * specifier-and-key is of valid length, and return the algorithm type if it
 113  * is.  Set *<b>legacy_out</b> to 1 iff this is a legacy password hash or
 114  * legacy specifier.  Return an error code on failure.
 115  */
 116 static int
 117 secret_to_key_get_type(const uint8_t *spec_and_key, size_t spec_and_key_len,
 118                        int key_included, int *legacy_out)
 119 {
 120   size_t legacy_len = S2K_RFC2440_SPECIFIER_LEN;
 121   uint8_t type;
 122   int total_len;
 123
 124   if (key_included)
 125     legacy_len += DIGEST_LEN;
 126
 127   if (spec_and_key_len == legacy_len) {
 128     *legacy_out = 1;
 129     return S2K_TYPE_RFC2440;
 130   }
 131
 132   *legacy_out = 0;
 133   if (spec_and_key_len == 0)
 134     return S2K_BAD_LEN;
 135
 136   type = spec_and_key[0];
 137   total_len = secret_to_key_spec_len(type);
 138   if (total_len < 0)
 139     return S2K_BAD_ALGORITHM;
 140   if (key_included) {
 141     int keylen = secret_to_key_key_len(type);
 142     if (keylen < 0)
 143       return S2K_BAD_ALGORITHM;
 144     total_len += keylen;
 145   }
 146
 147   if ((size_t)total_len + 1 == spec_and_key_len)
 148     return type;
 149   else
 150     return S2K_BAD_LEN;
 151 }
 152
 153 /**
 154  * Write a new random s2k specifier of type <b>type</b>, without prefixing
 155  * type byte, to <b>spec_out</b>, which must have enough room.  May adjust
 156  * parameter choice based on <b>flags</b>.
 157  */
 158 static int
 159 make_specifier(uint8_t *spec_out, uint8_t type, unsigned flags)
 160 {
 161   int speclen = secret_to_key_spec_len(type);
 162   if (speclen < 0)
 163       return S2K_BAD_ALGORITHM;
 164
 165   crypto_rand((char*)spec_out, speclen);
 166   switch (type) {
 167     case S2K_TYPE_RFC2440:
 168       /* Hash 64 k of data. */
 169       spec_out[S2K_RFC2440_SPECIFIER_LEN-1] = 96;
 170       break;
 171     case S2K_TYPE_PBKDF2:
 172       /* 131 K iterations */
 173       spec_out[PBKDF2_SPEC_LEN-1] = 17;
 174       break;
 175     case S2K_TYPE_SCRYPT:
 176       if (flags & S2K_FLAG_LOW_MEM) {
 177         /* N = 1<<12 */
 178         spec_out[SCRYPT_SPEC_LEN-2] = 12;
 179       } else {
 180         /* N = 1<<15 */
 181         spec_out[SCRYPT_SPEC_LEN-2] = 15;
 182       }
 183       /* r = 8; p = 2. */
 184       spec_out[SCRYPT_SPEC_LEN-1] = (3u << 4) | (1u << 0);
 185       break;
 186     // LCOV_EXCL_START - we should have returned above.
 187     default:
 188       tor_fragile_assert();
 189       return S2K_BAD_ALGORITHM;
 190     // LCOV_EXCL_STOP
 191   }
 192
 193   return speclen;
 194 }
 195
 196 /** Implement RFC2440-style iterated-salted S2K conversion: convert the
 197  * <b>secret_len</b>-byte <b>secret</b> into a <b>key_out_len</b> byte
 198  * <b>key_out</b>.  As in RFC2440, the first 8 bytes of s2k_specifier
 199  * are a salt; the 9th byte describes how much iteration to do.
 200  * If <b>key_out_len</b> &gt; DIGEST_LEN, use HDKF to expand the result.
 201  */
 202 void
 203 secret_to_key_rfc2440(char *key_out, size_t key_out_len, const char *secret,
 204               size_t secret_len, const char *s2k_specifier)
 205 {
 206   crypto_digest_t *d;
 207   uint8_t c;
 208   size_t count, tmplen;
 209   char *tmp;
 210   uint8_t buf[DIGEST_LEN];
 211   tor_assert(key_out_len < SIZE_T_CEILING);
 212
 213 #define EXPBIAS 6
 214   c = s2k_specifier[8];
 215   count = ((uint32_t)16 + (c & 15)) << ((c >> 4) + EXPBIAS);
 216 #undef EXPBIAS
 217
 218   d = crypto_digest_new();
 219   tmplen = 8+secret_len;
 220   tmp = tor_malloc(tmplen);
 221   memcpy(tmp,s2k_specifier,8);
 222   memcpy(tmp+8,secret,secret_len);
 223   secret_len += 8;
 224   while (count) {
 225     if (count >= secret_len) {
 226       crypto_digest_add_bytes(d, tmp, secret_len);
 227       count -= secret_len;
 228     } else {
 229       crypto_digest_add_bytes(d, tmp, count);
 230       count = 0;
 231     }
 232   }
 233   crypto_digest_get_digest(d, (char*)buf, sizeof(buf));
 234
 235   if (key_out_len <= sizeof(buf)) {
 236     memcpy(key_out, buf, key_out_len);
 237   } else {
 238     crypto_expand_key_material_rfc5869_sha256(buf, DIGEST_LEN,
 239                                            (const uint8_t*)s2k_specifier, 8,
 240                                            (const uint8_t*)"EXPAND", 6,
 241                                            (uint8_t*)key_out, key_out_len);
 242   }
 243   memwipe(tmp, 0, tmplen);
 244   memwipe(buf, 0, sizeof(buf));
 245   tor_free(tmp);
 246   crypto_digest_free(d);
 247 }
 248
 249 /**
 250  * Helper: given a valid specifier without prefix type byte in <b>spec</b>,
 251  * whose length must be correct, and given a secret passphrase <b>secret</b>
 252  * of length <b>secret_len</b>, compute the key and store it into
 253  * <b>key_out</b>, which must have enough room for secret_to_key_key_len(type)
 254  * bytes.  Return the number of bytes written on success and an error code
 255  * on failure.
 256  */
 257 STATIC int
 258 secret_to_key_compute_key(uint8_t *key_out, size_t key_out_len,
 259                           const uint8_t *spec, size_t spec_len,
 260                           const char *secret, size_t secret_len,
 261                           int type)
 262 {
 263   int rv;
 264   if (key_out_len > INT_MAX)
 265     return S2K_BAD_LEN;
 266
 267   switch (type) {
 268     case S2K_TYPE_RFC2440:
 269       secret_to_key_rfc2440((char*)key_out, key_out_len, secret, secret_len,
 270                             (const char*)spec);
 271       return (int)key_out_len;
 272
 273     case S2K_TYPE_PBKDF2: {
 274       uint8_t log_iters;
 275       if (spec_len < 1 || secret_len > INT_MAX || spec_len > INT_MAX)
 276         return S2K_BAD_LEN;
 277       log_iters = spec[spec_len-1];
 278       if (log_iters > 31)
 279         return S2K_BAD_PARAMS;
 280 #ifdef ENABLE_OPENSSL
 281       rv = PKCS5_PBKDF2_HMAC_SHA1(secret, (int)secret_len,
 282                                   spec, (int)spec_len-1,
 283                                   (1<<log_iters),
 284                                   (int)key_out_len, key_out);
 285       if (rv < 0)
 286         return S2K_FAILED;
 287       return (int)key_out_len;
 288 #else /* !defined(ENABLE_OPENSSL) */
 289       SECItem passItem = { .type = siBuffer,
 290                            .data = (unsigned char *) secret,
 291                            .len = (int)secret_len };
 292       SECItem saltItem = { .type = siBuffer,
 293                            .data = (unsigned char *) spec,
 294                            .len = (int)spec_len - 1 };
 295       SECAlgorithmID *alg = NULL;
 296       PK11SymKey *key = NULL;
 297
 298       rv = S2K_FAILED;
 299       alg = PK11_CreatePBEV2AlgorithmID(
 300                   SEC_OID_PKCS5_PBKDF2, SEC_OID_HMAC_SHA1, SEC_OID_HMAC_SHA1,
 301                   (int)key_out_len, (1<<log_iters), &saltItem);
 302       if (alg == NULL)
 303         return S2K_FAILED;
 304
 305       key = PK11_PBEKeyGen(NULL /* slot */,
 306                            alg,
 307                            &passItem,
 308                            false,
 309                            NULL);
 310
 311       SECStatus st = PK11_ExtractKeyValue(key);
 312       if (st != SECSuccess)
 313         goto nss_pbkdf_err;
 314
 315       const SECItem *iptr = PK11_GetKeyData(key);
 316       if (iptr == NULL)
 317         goto nss_pbkdf_err;
 318
 319       rv = MIN((int)iptr->len, (int)key_out_len);
 320       memcpy(key_out, iptr->data, rv);
 321
 322     nss_pbkdf_err:
 323       if (key)
 324         PK11_FreeSymKey(key);
 325       if (alg)
 326         SECOID_DestroyAlgorithmID(alg, PR_TRUE);
 327       return rv;
 328 #endif /* defined(ENABLE_OPENSSL) */
 329     }
 330
 331     case S2K_TYPE_SCRYPT: {
 332 #ifdef HAVE_SCRYPT
 333       uint8_t log_N, log_r, log_p;
 334       uint64_t N;
 335       uint32_t r, p;
 336       if (spec_len < 2)
 337         return S2K_BAD_LEN;
 338       log_N = spec[spec_len-2];
 339       log_r = (spec[spec_len-1]) >> 4;
 340       log_p = (spec[spec_len-1]) & 15;
 341       if (log_N > 63)
 342         return S2K_BAD_PARAMS;
 343       N = ((uint64_t)1) << log_N;
 344       r = 1u << log_r;
 345       p = 1u << log_p;
 346       rv = libscrypt_scrypt((const uint8_t*)secret, secret_len,
 347                             spec, spec_len-2, N, r, p, key_out, key_out_len);
 348       if (rv != 0)
 349         return S2K_FAILED;
 350       return (int)key_out_len;
 351 #else /* !defined(HAVE_SCRYPT) */
 352       return S2K_NO_SCRYPT_SUPPORT;
 353 #endif /* defined(HAVE_SCRYPT) */
 354     }
 355     default:
 356       return S2K_BAD_ALGORITHM;
 357   }
 358 }
 359
 360 /**
 361  * Given a specifier previously constructed with secret_to_key_make_specifier
 362  * in <b>spec</b> of length <b>spec_len</b>, and a secret password in
 363  * <b>secret</b> of length <b>secret_len</b>, generate <b>key_out_len</b>
 364  * bytes of cryptographic material in <b>key_out</b>.  The native output of
 365  * the secret-to-key function will be truncated if key_out_len is short, and
 366  * expanded with HKDF if key_out_len is long.  Returns S2K_OKAY on success,
 367  * and an error code on failure.
 368  */
 369 int
 370 secret_to_key_derivekey(uint8_t *key_out, size_t key_out_len,
 371                         const uint8_t *spec, size_t spec_len,
 372                         const char *secret, size_t secret_len)
 373 {
 374   int legacy_format = 0;
 375   int type = secret_to_key_get_type(spec, spec_len, 0, &legacy_format);
 376   int r;
 377
 378   if (type < 0)
 379     return type;
 380 #ifndef HAVE_SCRYPT
 381   if (type == S2K_TYPE_SCRYPT)
 382     return S2K_NO_SCRYPT_SUPPORT;
 383 #endif
 384
 385   if (! legacy_format) {
 386     ++spec;
 387     --spec_len;
 388   }
 389
 390   r = secret_to_key_compute_key(key_out, key_out_len, spec, spec_len,
 391                                 secret, secret_len, type);
 392   if (r < 0)
 393     return r;
 394   else
 395     return S2K_OKAY;
 396 }
 397
 398 /**
 399  * Construct a new s2k algorithm specifier and salt in <b>buf</b>, according
 400  * to the bitwise-or of some S2K_FLAG_* options in <b>flags</b>.  Up to
 401  * <b>buf_len</b> bytes of storage may be used in <b>buf</b>.  Return the
 402  * number of bytes used on success and an error code on failure.
 403  */
 404 int
 405 secret_to_key_make_specifier(uint8_t *buf, size_t buf_len, unsigned flags)
 406 {
 407   int rv;
 408   int spec_len;
 409 #ifdef HAVE_SCRYPT
 410   uint8_t type = S2K_TYPE_SCRYPT;
 411 #else
 412   uint8_t type = S2K_TYPE_RFC2440;
 413 #endif
 414
 415   if (flags & S2K_FLAG_NO_SCRYPT)
 416     type = S2K_TYPE_RFC2440;
 417   if (flags & S2K_FLAG_USE_PBKDF2)
 418     type = S2K_TYPE_PBKDF2;
 419
 420   spec_len = secret_to_key_spec_len(type);
 421
 422   if ((int)buf_len < spec_len + 1)
 423     return S2K_TRUNCATED;
 424
 425   buf[0] = type;
 426   rv = make_specifier(buf+1, type, flags);
 427   if (rv < 0)
 428     return rv;
 429   else
 430     return rv + 1;
 431 }
 432
 433 /**
 434  * Hash a passphrase from <b>secret</b> of length <b>secret_len</b>, according
 435  * to the bitwise-or of some S2K_FLAG_* options in <b>flags</b>, and store the
 436  * hash along with salt and hashing parameters into <b>buf</b>.  Up to
 437  * <b>buf_len</b> bytes of storage may be used in <b>buf</b>.  Set
 438  * *<b>len_out</b> to the number of bytes used and return S2K_OKAY on success;
 439  * and return an error code on failure.
 440  */
 441 int
 442 secret_to_key_new(uint8_t *buf,
 443                   size_t buf_len,
 444                   size_t *len_out,
 445                   const char *secret, size_t secret_len,
 446                   unsigned flags)
 447 {
 448   int key_len;
 449   int spec_len;
 450   int type;
 451   int rv;
 452
 453   spec_len = secret_to_key_make_specifier(buf, buf_len, flags);
 454
 455   if (spec_len < 0)
 456     return spec_len;
 457
 458   type = buf[0];
 459   key_len = secret_to_key_key_len(type);
 460
 461   if (key_len < 0)
 462     return key_len;
 463
 464   if ((int)buf_len < key_len + spec_len)
 465     return S2K_TRUNCATED;
 466
 467   rv = secret_to_key_compute_key(buf + spec_len, key_len,
 468                                  buf + 1, spec_len-1,
 469                                  secret, secret_len, type);
 470   if (rv < 0)
 471     return rv;
 472
 473   *len_out = spec_len + key_len;
 474
 475   return S2K_OKAY;
 476 }
 477
 478 /**
 479  * Given a hashed passphrase in <b>spec_and_key</b> of length
 480  * <b>spec_and_key_len</b> as generated by secret_to_key_new(), verify whether
 481  * it is a hash of the passphrase <b>secret</b> of length <b>secret_len</b>.
 482  * Return S2K_OKAY on a match, S2K_BAD_SECRET on a well-formed hash that
 483  * doesn't match this secret, and another error code on other errors.
 484  */
 485 int
 486 secret_to_key_check(const uint8_t *spec_and_key, size_t spec_and_key_len,
 487                     const char *secret, size_t secret_len)
 488 {
 489   int is_legacy = 0;
 490   int type = secret_to_key_get_type(spec_and_key, spec_and_key_len,
 491                                     1, &is_legacy);
 492   uint8_t buf[32];
 493   int spec_len;
 494   int key_len;
 495   int rv;
 496
 497   if (type < 0)
 498     return type;
 499
 500   if (! is_legacy) {
 501     spec_and_key++;
 502     spec_and_key_len--;
 503   }
 504
 505   spec_len = secret_to_key_spec_len(type);
 506   key_len = secret_to_key_key_len(type);
 507   tor_assert(spec_len > 0);
 508   tor_assert(key_len > 0);
 509   tor_assert(key_len <= (int) sizeof(buf));
 510   tor_assert((int)spec_and_key_len == spec_len + key_len);
 511   rv = secret_to_key_compute_key(buf, key_len,
 512                                  spec_and_key, spec_len,
 513                                  secret, secret_len, type);
 514   if (rv < 0)
 515     goto done;
 516
 517   if (tor_memeq(buf, spec_and_key + spec_len, key_len))
 518     rv = S2K_OKAY;
 519   else
 520     rv = S2K_BAD_SECRET;
 521
 522  done:
 523   memwipe(buf, 0, sizeof(buf));
 524   return rv;
 525 }