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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 /* OAEP Padding for PKCS #1 -- 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_oaep_decode(const unsigned char *msg, unsigned long msglen, |
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18 const unsigned char *lparam, unsigned long lparamlen, |
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19 unsigned long modulus_bitlen, int hash_idx, |
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20 unsigned char *out, unsigned long *outlen, |
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21 int *res) |
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22 { |
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23 unsigned char DB[1024], seed[MAXBLOCKSIZE], mask[sizeof(DB)]; |
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24 unsigned long hLen, x, y, modulus_len; |
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25 int err; |
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26 |
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27 _ARGCHK(msg != NULL); |
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28 _ARGCHK(out != NULL); |
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29 _ARGCHK(outlen != NULL); |
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30 _ARGCHK(res != NULL); |
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31 |
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32 /* default to invalid packet */ |
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33 *res = 0; |
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34 |
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35 /* test valid hash */ |
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36 if ((err = hash_is_valid(hash_idx)) != CRYPT_OK) { |
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37 return err; |
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38 } |
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39 hLen = hash_descriptor[hash_idx].hashsize; |
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40 modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0); |
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41 |
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42 /* test message size */ |
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43 if (modulus_len >= sizeof(DB) || msglen != modulus_len) { |
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44 return CRYPT_PK_INVALID_SIZE; |
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45 } |
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46 |
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47 /* ok so it's now in the form |
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48 |
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49 0x00 || maskedseed || maskedDB |
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50 |
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51 1 || hLen || modulus_len - hLen - 1 |
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52 |
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53 */ |
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54 |
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55 /* must have leading 0x00 byte */ |
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56 if (msg[0] != 0x00) { |
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57 return CRYPT_OK; |
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58 } |
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59 |
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60 /* now read the masked seed */ |
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61 for (x = 1, y = 0; y < hLen; y++) { |
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62 seed[y] = msg[x++]; |
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63 } |
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64 |
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65 /* now read the masked DB */ |
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66 for (y = 0; y < modulus_len - hLen - 1; y++) { |
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67 DB[y] = msg[x++]; |
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68 } |
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69 |
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70 /* compute MGF1 of maskedDB (hLen) */ |
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71 if ((err = pkcs_1_mgf1(DB, modulus_len - hLen - 1, hash_idx, mask, hLen)) != CRYPT_OK) { |
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72 return err; |
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73 } |
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74 |
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75 /* XOR against seed */ |
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76 for (y = 0; y < hLen; y++) { |
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77 seed[y] ^= mask[y]; |
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78 } |
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79 |
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80 /* compute MGF1 of seed (k - hlen - 1) */ |
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81 if ((err = pkcs_1_mgf1(seed, hLen, hash_idx, mask, modulus_len - hLen - 1)) != CRYPT_OK) { |
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82 return err; |
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83 } |
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84 |
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85 /* xor against DB */ |
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86 for (y = 0; y < (modulus_len - hLen - 1); y++) { |
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87 DB[y] ^= mask[y]; |
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88 } |
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89 |
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90 /* now DB == lhash || PS || 0x01 || M, PS == k - mlen - 2hlen - 2 zeroes */ |
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91 |
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92 /* compute lhash and store it in seed [reuse temps!] */ |
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93 x = sizeof(seed); |
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94 if (lparam != NULL) { |
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95 if ((err = hash_memory(hash_idx, lparam, lparamlen, seed, &x)) != CRYPT_OK) { |
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96 return err; |
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97 } |
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98 } else { |
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99 /* can't pass hash_memory a NULL so use DB with zero length */ |
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100 if ((err = hash_memory(hash_idx, DB, 0, seed, &x)) != CRYPT_OK) { |
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101 return err; |
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102 } |
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103 } |
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104 |
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105 /* compare the lhash'es */ |
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106 if (memcmp(seed, DB, hLen) != 0) { |
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107 return CRYPT_OK; |
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108 } |
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109 |
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110 /* now zeroes before a 0x01 */ |
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111 for (x = hLen; x < (modulus_len - hLen - 1) && DB[x] == 0x00; x++) { |
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112 /* step... */ |
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113 } |
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114 |
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115 /* error out if wasn't 0x01 */ |
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116 if (x == (modulus_len - hLen - 1) || DB[x] != 0x01) { |
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117 return CRYPT_OK; |
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118 } |
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119 |
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120 /* rest is the message (and skip 0x01) */ |
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121 if (msglen - ++x > *outlen) { |
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122 return CRYPT_BUFFER_OVERFLOW; |
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123 } |
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124 |
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125 /* copy message */ |
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126 *outlen = (modulus_len - hLen - 1) - x; |
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127 for (y = 0; x != (modulus_len - hLen - 1); ) { |
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128 out[y++] = DB[x++]; |
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129 } |
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130 |
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131 #ifdef CLEAN_STACK |
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132 zeromem(DB, sizeof(DB)); |
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133 zeromem(seed, sizeof(seed)); |
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134 zeromem(mask, sizeof(mask)); |
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135 #endif |
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136 |
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137 /* valid packet */ |
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138 *res = 1; |
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139 |
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140 return CRYPT_OK; |
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141 } |
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142 |
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143 #endif /* PKCS_1 */ |
