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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 /** @file pkcs_1_v1_5_decode.c |
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14 * |
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15 * PKCS #1 v1.5 Padding. (Andreas Lange) |
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16 */ |
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17 |
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18 #ifdef PKCS_1 |
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19 |
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20 /** @brief PKCS #1 v1.5 decode. |
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21 * |
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22 * @param msg The encoded data to decode |
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23 * @param msglen The length of the encoded data (octets) |
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24 * @param block_type Block type to use in padding (\sa ltc_pkcs_1_v1_5_blocks) |
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25 * @param modulus_bitlen The bit length of the RSA modulus |
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26 * @param out [out] Destination of decoding |
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27 * @param outlen [in/out] The max size and resulting size of the decoding |
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28 * @param is_valid [out] Boolean whether the padding was valid |
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29 * |
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30 * @return CRYPT_OK if successful (even if invalid) |
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31 */ |
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32 int pkcs_1_v1_5_decode(const unsigned char *msg, |
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33 unsigned long msglen, |
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34 int block_type, |
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35 unsigned long modulus_bitlen, |
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36 unsigned char *out, |
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37 unsigned long *outlen, |
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38 int *is_valid) |
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39 { |
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40 unsigned long modulus_len, ps_len, i; |
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41 int result; |
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42 |
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43 /* default to invalid packet */ |
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44 *is_valid = 0; |
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45 |
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46 modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0); |
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47 |
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48 /* test message size */ |
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49 |
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50 if ((msglen > modulus_len) || (modulus_len < 11)) { |
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51 return CRYPT_PK_INVALID_SIZE; |
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52 } |
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53 |
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54 /* separate encoded message */ |
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55 |
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56 if ((msg[0] != 0x00) || (msg[1] != (unsigned char)block_type)) { |
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57 result = CRYPT_INVALID_PACKET; |
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58 goto bail; |
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59 } |
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60 |
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61 if (block_type == LTC_PKCS_1_EME) { |
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62 for (i = 2; i < modulus_len; i++) { |
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63 /* separator */ |
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64 if (msg[i] == 0x00) { break; } |
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65 } |
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66 ps_len = i++ - 2; |
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67 |
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68 if ((i >= modulus_len) || (ps_len < 8)) { |
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69 /* There was no octet with hexadecimal value 0x00 to separate ps from m, |
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70 * or the length of ps is less than 8 octets. |
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71 */ |
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72 result = CRYPT_INVALID_PACKET; |
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73 goto bail; |
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74 } |
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75 } else { |
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76 for (i = 2; i < modulus_len - 1; i++) { |
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77 if (msg[i] != 0xFF) { break; } |
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78 } |
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79 |
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80 /* separator check */ |
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81 if (msg[i] != 0) { |
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82 /* There was no octet with hexadecimal value 0x00 to separate ps from m. */ |
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83 result = CRYPT_INVALID_PACKET; |
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84 goto bail; |
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85 } |
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86 |
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87 ps_len = i - 2; |
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88 } |
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89 |
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90 if (*outlen < (msglen - (2 + ps_len + 1))) { |
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91 *outlen = msglen - (2 + ps_len + 1); |
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92 result = CRYPT_BUFFER_OVERFLOW; |
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93 goto bail; |
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94 } |
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95 |
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96 *outlen = (msglen - (2 + ps_len + 1)); |
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97 XMEMCPY(out, &msg[2 + ps_len + 1], *outlen); |
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98 |
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99 /* valid packet */ |
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100 *is_valid = 1; |
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101 result = CRYPT_OK; |
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102 bail: |
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103 return result; |
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104 } /* pkcs_1_v1_5_decode */ |
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105 |
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106 #endif /* #ifdef PKCS_1 */ |
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107 |
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108 /* $Source: /cvs/libtom/libtomcrypt/src/pk/pkcs1/pkcs_1_v1_5_decode.c,v $ */ |
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109 /* $Revision: 1.5 $ */ |
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110 /* $Date: 2006/12/16 17:41:21 $ */ |
