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1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis |
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2 * |
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3 * LibTomCrypt is a library that provides various cryptographic |
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4 * algorithms in a highly modular and flexible manner. |
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5 * |
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6 * The library is free for all purposes without any express |
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7 * guarantee it works. |
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8 * |
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9 * Tom St Denis, [email protected], http://libtomcrypt.org |
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10 */ |
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11 #include "mycrypt.h" |
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12 |
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13 /* PKCS #1 PSS Signature Padding -- Tom St Denis */ |
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14 |
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15 #ifdef PKCS_1 |
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16 |
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17 int pkcs_1_pss_decode(const unsigned char *msghash, unsigned long msghashlen, |
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18 const unsigned char *sig, unsigned long siglen, |
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19 unsigned long saltlen, int hash_idx, |
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20 unsigned long modulus_bitlen, int *res) |
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21 { |
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22 unsigned char DB[1024], mask[sizeof(DB)], salt[sizeof(DB)], hash[sizeof(DB)]; |
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23 unsigned long x, y, hLen, modulus_len; |
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24 int err; |
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25 hash_state md; |
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26 |
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27 _ARGCHK(msghash != NULL); |
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28 _ARGCHK(res != NULL); |
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29 |
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30 /* default to invalid */ |
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31 *res = 0; |
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32 |
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33 /* ensure hash is valid */ |
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34 if ((err = hash_is_valid(hash_idx)) != CRYPT_OK) { |
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35 return err; |
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36 } |
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37 |
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38 hLen = hash_descriptor[hash_idx].hashsize; |
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39 modulus_len = (modulus_bitlen>>3) + (modulus_bitlen & 7 ? 1 : 0); |
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40 |
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41 /* check sizes */ |
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42 if ((saltlen > sizeof(salt)) || (modulus_len > sizeof(DB)) || |
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43 (modulus_len < hLen + saltlen + 2) || (siglen != modulus_len)) { |
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44 return CRYPT_INVALID_ARG; |
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45 } |
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46 |
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47 /* ensure the 0xBC byte */ |
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48 if (sig[siglen-1] != 0xBC) { |
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49 return CRYPT_OK; |
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50 } |
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51 |
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52 /* copy out the DB */ |
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53 for (x = 0; x < modulus_len - hLen - 1; x++) { |
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54 DB[x] = sig[x]; |
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55 } |
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56 |
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57 /* copy out the hash */ |
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58 for (y = 0; y < hLen; y++) { |
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59 hash[y] = sig[x++]; |
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60 } |
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61 |
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62 /* check the MSB */ |
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63 if ((sig[0] & ~(0xFF >> ((modulus_len<<3) - (modulus_bitlen-1)))) != 0) { |
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64 return CRYPT_OK; |
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65 } |
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66 |
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67 /* generate mask of length modulus_len - hLen - 1 from hash */ |
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68 if ((err = pkcs_1_mgf1(hash, hLen, hash_idx, mask, modulus_len - hLen - 1)) != CRYPT_OK) { |
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69 return err; |
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70 } |
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71 |
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72 /* xor against DB */ |
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73 for (y = 0; y < (modulus_len - hLen - 1); y++) { |
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74 DB[y] ^= mask[y]; |
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75 } |
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76 |
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77 /* now clear the first byte [make sure smaller than modulus] */ |
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78 DB[0] &= 0xFF >> ((modulus_len<<3) - (modulus_bitlen-1)); |
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79 |
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80 /* DB = PS || 0x01 || salt, PS == modulus_len - saltlen - hLen - 2 zero bytes */ |
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81 |
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82 /* check for zeroes and 0x01 */ |
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83 for (x = 0; x < modulus_len - saltlen - hLen - 2; x++) { |
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84 if (DB[x] != 0x00) { |
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85 return CRYPT_OK; |
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86 } |
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87 } |
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88 |
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89 if (DB[x++] != 0x01) { |
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90 return CRYPT_OK; |
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91 } |
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92 |
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93 /* M = (eight) 0x00 || msghash || salt, mask = H(M) */ |
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94 hash_descriptor[hash_idx].init(&md); |
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95 zeromem(mask, 8); |
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96 if ((err = hash_descriptor[hash_idx].process(&md, mask, 8)) != CRYPT_OK) { |
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97 return err; |
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98 } |
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99 if ((err = hash_descriptor[hash_idx].process(&md, msghash, msghashlen)) != CRYPT_OK) { |
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100 return err; |
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101 } |
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102 if ((err = hash_descriptor[hash_idx].process(&md, DB+x, saltlen)) != CRYPT_OK) { |
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103 return err; |
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104 } |
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105 if ((err = hash_descriptor[hash_idx].done(&md, mask)) != CRYPT_OK) { |
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106 return err; |
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107 } |
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108 |
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109 /* mask == hash means valid signature */ |
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110 if (memcmp(mask, hash, hLen) == 0) { |
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111 *res = 1; |
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112 } |
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113 |
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114 #ifdef CLEAN_STACK |
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115 zeromem(DB, sizeof(DB)); |
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116 zeromem(mask, sizeof(mask)); |
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117 zeromem(salt, sizeof(salt)); |
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118 zeromem(hash, sizeof(hash)); |
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119 #endif |
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120 |
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121 return CRYPT_OK; |
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122 } |
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123 |
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124 #endif /* PKCS_1 */ |
