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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_encode(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, prng_state *prng, |
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20 int prng_idx, int hash_idx, |
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21 unsigned char *out, unsigned long *outlen) |
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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 |
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31 /* test valid hash */ |
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32 if ((err = hash_is_valid(hash_idx)) != CRYPT_OK) { |
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33 return err; |
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34 } |
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35 |
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36 /* valid prng */ |
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37 if ((err = prng_is_valid(prng_idx)) != CRYPT_OK) { |
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38 return err; |
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39 } |
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40 |
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41 hLen = hash_descriptor[hash_idx].hashsize; |
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42 modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0); |
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43 |
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44 /* test message size */ |
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45 if (modulus_len >= sizeof(DB) || msglen > (modulus_len - 2*hLen - 2)) { |
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46 return CRYPT_PK_INVALID_SIZE; |
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47 } |
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48 |
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49 /* get lhash */ |
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50 // DB == lhash || PS || 0x01 || M, PS == k - mlen - 2hlen - 2 zeroes |
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51 x = sizeof(DB); |
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52 if (lparam != NULL) { |
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53 if ((err = hash_memory(hash_idx, lparam, lparamlen, DB, &x)) != CRYPT_OK) { |
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54 return err; |
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55 } |
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56 } else { |
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57 /* can't pass hash_memory a NULL so use DB with zero length */ |
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58 if ((err = hash_memory(hash_idx, DB, 0, DB, &x)) != CRYPT_OK) { |
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59 return err; |
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60 } |
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61 } |
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62 |
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63 /* append PS then 0x01 (to lhash) */ |
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64 x = hLen; |
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65 y = modulus_len - msglen - 2*hLen - 2; |
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66 while (y--) { |
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67 DB[x++] = 0x00; |
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68 } |
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69 DB[x++] = 0x01; |
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70 |
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71 /* message */ |
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72 y = msglen; |
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73 while (y--) { |
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74 DB[x++] = *msg++; |
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75 } |
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76 |
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77 /* now choose a random seed */ |
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78 if (prng_descriptor[prng_idx].read(seed, hLen, prng) != hLen) { |
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79 return CRYPT_ERROR_READPRNG; |
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80 } |
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81 |
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82 /* compute MGF1 of seed (k - hlen - 1) */ |
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83 if ((err = pkcs_1_mgf1(seed, hLen, hash_idx, mask, modulus_len - hLen - 1)) != CRYPT_OK) { |
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84 return err; |
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85 } |
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86 |
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87 /* xor against DB */ |
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88 for (y = 0; y < (modulus_len - hLen - 1); y++) { |
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89 DB[y] ^= mask[y]; |
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90 } |
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91 |
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92 /* compute MGF1 of maskedDB (hLen) */ |
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93 if ((err = pkcs_1_mgf1(DB, modulus_len - hLen - 1, hash_idx, mask, hLen)) != CRYPT_OK) { |
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94 return err; |
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95 } |
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96 |
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97 /* XOR against seed */ |
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98 for (y = 0; y < hLen; y++) { |
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99 seed[y] ^= mask[y]; |
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100 } |
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101 |
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102 /* create string of length modulus_len */ |
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103 if (*outlen < modulus_len) { |
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104 return CRYPT_BUFFER_OVERFLOW; |
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105 } |
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106 |
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107 /* start output which is 0x00 || maskedSeed || maskedDB */ |
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108 x = 0; |
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109 out[x++] = 0x00; |
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110 for (y = 0; y < hLen; y++) { |
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111 out[x++] = seed[y]; |
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112 } |
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113 for (y = 0; y < modulus_len - hLen - 1; y++) { |
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114 out[x++] = DB[y]; |
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115 } |
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116 *outlen = x; |
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117 |
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118 #ifdef CLEAN_STACK |
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119 zeromem(DB, sizeof(DB)); |
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120 zeromem(seed, sizeof(seed)); |
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121 zeromem(mask, sizeof(mask)); |
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122 #endif |
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123 |
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124 return CRYPT_OK; |
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125 } |
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126 |
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127 #endif /* PKCS_1 */ |
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128 |
