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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.com |
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10 */ |
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11 #include "tomcrypt.h" |
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12 |
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13 /** |
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14 @file dsa_decrypt_key.c |
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15 DSA Crypto, Tom St Denis |
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16 */ |
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17 |
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18 #ifdef MDSA |
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19 |
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20 /** |
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21 Decrypt an DSA encrypted key |
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22 @param in The ciphertext |
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23 @param inlen The length of the ciphertext (octets) |
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24 @param out [out] The plaintext |
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25 @param outlen [in/out] The max size and resulting size of the plaintext |
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26 @param key The corresponding private DSA key |
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27 @return CRYPT_OK if successful |
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28 */ |
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29 int dsa_decrypt_key(const unsigned char *in, unsigned long inlen, |
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30 unsigned char *out, unsigned long *outlen, |
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31 dsa_key *key) |
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32 { |
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33 unsigned char *skey, *expt; |
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34 void *g_pub; |
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35 unsigned long x, y, hashOID[32]; |
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36 int hash, err; |
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37 ltc_asn1_list decode[3]; |
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38 |
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39 LTC_ARGCHK(in != NULL); |
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40 LTC_ARGCHK(out != NULL); |
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41 LTC_ARGCHK(outlen != NULL); |
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42 LTC_ARGCHK(key != NULL); |
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43 |
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44 /* right key type? */ |
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45 if (key->type != PK_PRIVATE) { |
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46 return CRYPT_PK_NOT_PRIVATE; |
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47 } |
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48 |
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49 /* decode to find out hash */ |
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50 LTC_SET_ASN1(decode, 0, LTC_ASN1_OBJECT_IDENTIFIER, hashOID, sizeof(hashOID)/sizeof(hashOID[0])); |
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51 |
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52 if ((err = der_decode_sequence(in, inlen, decode, 1)) != CRYPT_OK) { |
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53 return err; |
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54 } |
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55 |
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56 hash = find_hash_oid(hashOID, decode[0].size); |
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57 if (hash_is_valid(hash) != CRYPT_OK) { |
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58 return CRYPT_INVALID_PACKET; |
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59 } |
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60 |
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61 /* we now have the hash! */ |
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62 |
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63 if ((err = mp_init(&g_pub)) != CRYPT_OK) { |
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64 return err; |
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65 } |
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66 |
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67 /* allocate memory */ |
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68 expt = XMALLOC(mp_unsigned_bin_size(key->p) + 1); |
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69 skey = XMALLOC(MAXBLOCKSIZE); |
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70 if (expt == NULL || skey == NULL) { |
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71 if (expt != NULL) { |
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72 XFREE(expt); |
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73 } |
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74 if (skey != NULL) { |
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75 XFREE(skey); |
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76 } |
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77 mp_clear(g_pub); |
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78 return CRYPT_MEM; |
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79 } |
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80 |
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81 LTC_SET_ASN1(decode, 1, LTC_ASN1_INTEGER, g_pub, 1UL); |
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82 LTC_SET_ASN1(decode, 2, LTC_ASN1_OCTET_STRING, skey, MAXBLOCKSIZE); |
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83 |
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84 /* read the structure in now */ |
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85 if ((err = der_decode_sequence(in, inlen, decode, 3)) != CRYPT_OK) { |
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86 goto LBL_ERR; |
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87 } |
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88 |
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89 /* make shared key */ |
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90 x = mp_unsigned_bin_size(key->p) + 1; |
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91 if ((err = dsa_shared_secret(key->x, g_pub, key, expt, &x)) != CRYPT_OK) { |
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92 goto LBL_ERR; |
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93 } |
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94 |
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95 y = MIN(mp_unsigned_bin_size(key->p) + 1, MAXBLOCKSIZE); |
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96 if ((err = hash_memory(hash, expt, x, expt, &y)) != CRYPT_OK) { |
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97 goto LBL_ERR; |
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98 } |
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99 |
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100 /* ensure the hash of the shared secret is at least as big as the encrypt itself */ |
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101 if (decode[2].size > y) { |
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102 err = CRYPT_INVALID_PACKET; |
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103 goto LBL_ERR; |
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104 } |
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105 |
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106 /* avoid buffer overflow */ |
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107 if (*outlen < decode[2].size) { |
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108 *outlen = decode[2].size; |
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109 err = CRYPT_BUFFER_OVERFLOW; |
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110 goto LBL_ERR; |
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111 } |
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112 |
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113 /* Decrypt the key */ |
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114 for (x = 0; x < decode[2].size; x++) { |
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115 out[x] = expt[x] ^ skey[x]; |
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116 } |
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117 *outlen = x; |
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118 |
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119 err = CRYPT_OK; |
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120 LBL_ERR: |
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121 #ifdef LTC_CLEAN_STACK |
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122 zeromem(expt, mp_unsigned_bin_size(key->p) + 1); |
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123 zeromem(skey, MAXBLOCKSIZE); |
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124 #endif |
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125 |
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126 XFREE(expt); |
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127 XFREE(skey); |
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128 |
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129 mp_clear(g_pub); |
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130 |
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131 return err; |
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132 } |
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133 |
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134 #endif |
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135 |
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136 /* $Source: /cvs/libtom/libtomcrypt/src/pk/dsa/dsa_decrypt_key.c,v $ */ |
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137 /* $Revision: 1.9 $ */ |
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138 /* $Date: 2006/12/04 03:18:43 $ */ |
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139 |
