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annotate pkcs_1_pss_decode.c @ 0:d7da3b1e1540 libtomcrypt

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put back the 0.95 makefile which was inadvertently merged over
author Matt Johnston <matt@ucc.asn.au>
date Mon, 31 May 2004 18:21:40 +0000
parents
children 6362d3854bb4
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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))) != 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 /* DB = PS || 0x01 || salt, PS == modulus_len - saltlen - hLen - 2 zero bytes */
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78
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79 /* check for zeroes and 0x01 */
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80 for (x = 0; x < modulus_len - saltlen - hLen - 2; x++) {
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81 if (DB[x] != 0x00) {
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82 return CRYPT_OK;
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83 }
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84 }
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85
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86 if (DB[x++] != 0x01) {
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87 return CRYPT_OK;
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88 }
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89
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90 /* M = (eight) 0x00 || msghash || salt, mask = H(M) */
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91 hash_descriptor[hash_idx].init(&md);
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92 zeromem(mask, 8);
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93 if ((err = hash_descriptor[hash_idx].process(&md, mask, 8)) != CRYPT_OK) {
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94 return err;
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95 }
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96 if ((err = hash_descriptor[hash_idx].process(&md, msghash, msghashlen)) != 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, DB+x, saltlen)) != 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].done(&md, mask)) != CRYPT_OK) {
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103 return err;
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104 }
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105
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106 /* mask == hash means valid signature */
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107 if (memcmp(mask, hash, hLen) == 0) {
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108 *res = 1;
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109 }
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110
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111 #ifdef CLEAN_STACK
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112 zeromem(DB, sizeof(DB));
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113 zeromem(mask, sizeof(mask));
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114 zeromem(salt, sizeof(salt));
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115 zeromem(hash, sizeof(hash));
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116 #endif
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117
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118 return CRYPT_OK;
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119 }
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120
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121 #endif /* PKCS_1 */