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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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143
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22 unsigned char *DB, *mask, *salt, *hash; |
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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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143
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41 /* allocate ram for DB/mask/salt/hash of size modulus_len */ |
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42 DB = XMALLOC(modulus_len); |
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43 mask = XMALLOC(modulus_len); |
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44 salt = XMALLOC(modulus_len); |
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45 hash = XMALLOC(modulus_len); |
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46 if (DB == NULL || mask == NULL || salt == NULL || hash == NULL) { |
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47 if (DB != NULL) { |
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48 XFREE(DB); |
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49 } |
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50 if (mask != NULL) { |
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51 XFREE(mask); |
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52 } |
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53 if (salt != NULL) { |
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54 XFREE(salt); |
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55 } |
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56 if (hash != NULL) { |
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57 XFREE(hash); |
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58 } |
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59 return CRYPT_MEM; |
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60 } |
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61 |
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62 /* check sizes */ |
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143
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63 if ((saltlen > modulus_len) || |
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64 (modulus_len < hLen + saltlen + 2) || (siglen != modulus_len)) { |
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143
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65 err = CRYPT_INVALID_ARG; |
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66 goto __ERR; |
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67 } |
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68 |
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69 /* ensure the 0xBC byte */ |
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70 if (sig[siglen-1] != 0xBC) { |
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143
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71 err = CRYPT_OK; |
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72 goto __ERR; |
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73 } |
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74 |
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75 /* copy out the DB */ |
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76 for (x = 0; x < modulus_len - hLen - 1; x++) { |
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77 DB[x] = sig[x]; |
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78 } |
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79 |
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80 /* copy out the hash */ |
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81 for (y = 0; y < hLen; y++) { |
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82 hash[y] = sig[x++]; |
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83 } |
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84 |
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85 /* check the MSB */ |
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86 if ((sig[0] & ~(0xFF >> ((modulus_len<<3) - (modulus_bitlen-1)))) != 0) { |
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143
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87 err = CRYPT_OK; |
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88 goto __ERR; |
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89 } |
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90 |
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91 /* generate mask of length modulus_len - hLen - 1 from hash */ |
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92 if ((err = pkcs_1_mgf1(hash, hLen, hash_idx, mask, modulus_len - hLen - 1)) != CRYPT_OK) { |
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143
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93 goto __ERR; |
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94 } |
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95 |
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96 /* xor against DB */ |
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97 for (y = 0; y < (modulus_len - hLen - 1); y++) { |
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98 DB[y] ^= mask[y]; |
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99 } |
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100 |
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101 /* now clear the first byte [make sure smaller than modulus] */ |
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102 DB[0] &= 0xFF >> ((modulus_len<<3) - (modulus_bitlen-1)); |
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103 |
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104 /* DB = PS || 0x01 || salt, PS == modulus_len - saltlen - hLen - 2 zero bytes */ |
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105 |
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106 /* check for zeroes and 0x01 */ |
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107 for (x = 0; x < modulus_len - saltlen - hLen - 2; x++) { |
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108 if (DB[x] != 0x00) { |
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143
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109 err = CRYPT_OK; |
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110 goto __ERR; |
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111 } |
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112 } |
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113 |
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143
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114 /* check for the 0x01 */ |
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115 if (DB[x++] != 0x01) { |
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116 err = CRYPT_OK; |
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117 goto __ERR; |
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118 } |
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119 |
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120 /* M = (eight) 0x00 || msghash || salt, mask = H(M) */ |
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121 if ((err = hash_descriptor[hash_idx].init(&md)) != CRYPT_OK) { |
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122 goto __ERR; |
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123 } |
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124 zeromem(mask, 8); |
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125 if ((err = hash_descriptor[hash_idx].process(&md, mask, 8)) != CRYPT_OK) { |
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126 goto __ERR; |
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127 } |
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128 if ((err = hash_descriptor[hash_idx].process(&md, msghash, msghashlen)) != CRYPT_OK) { |
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129 goto __ERR; |
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130 } |
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131 if ((err = hash_descriptor[hash_idx].process(&md, DB+x, saltlen)) != CRYPT_OK) { |
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132 goto __ERR; |
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133 } |
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134 if ((err = hash_descriptor[hash_idx].done(&md, mask)) != CRYPT_OK) { |
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135 goto __ERR; |
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136 } |
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137 |
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138 /* mask == hash means valid signature */ |
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139 if (memcmp(mask, hash, hLen) == 0) { |
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140 *res = 1; |
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141 } |
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142 |
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143
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143 err = CRYPT_OK; |
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144 __ERR: |
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145 #ifdef CLEAN_STACK |
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143
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146 zeromem(DB, modulus_len); |
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147 zeromem(mask, modulus_len); |
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148 zeromem(salt, modulus_len); |
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149 zeromem(hash, modulus_len); |
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150 #endif |
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151 |
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143
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152 XFREE(hash); |
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153 XFREE(salt); |
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154 XFREE(mask); |
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155 XFREE(DB); |
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156 |
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157 return err; |
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158 } |
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159 |
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160 #endif /* PKCS_1 */ |
