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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_encode.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 encode. |
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21 * |
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22 * \param msg The data to encode |
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23 * \param msglen The length of the data to encode (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 prng An active PRNG state (only for LTC_PKCS_1_EME) |
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27 * \param prng_idx The index of the PRNG desired (only for LTC_PKCS_1_EME) |
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28 * \param out [out] The destination for the encoded data |
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29 * \param outlen [in/out] The max size and resulting size of the encoded data |
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30 * |
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31 * \return CRYPT_OK if successful |
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32 */ |
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33 int pkcs_1_v1_5_encode(const unsigned char *msg, |
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34 unsigned long msglen, |
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35 int block_type, |
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36 unsigned long modulus_bitlen, |
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37 prng_state *prng, |
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38 int prng_idx, |
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39 unsigned char *out, |
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40 unsigned long *outlen) |
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41 { |
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42 unsigned long modulus_len, ps_len, i; |
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43 unsigned char *ps; |
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44 int result; |
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45 |
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46 /* valid block_type? */ |
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47 if ((block_type != LTC_PKCS_1_EMSA) && |
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48 (block_type != LTC_PKCS_1_EME)) { |
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49 return CRYPT_PK_INVALID_PADDING; |
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50 } |
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51 |
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52 if (block_type == LTC_PKCS_1_EME) { /* encryption padding, we need a valid PRNG */ |
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53 if ((result = prng_is_valid(prng_idx)) != CRYPT_OK) { |
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54 return result; |
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55 } |
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56 } |
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57 |
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58 modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0); |
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59 |
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60 /* test message size */ |
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61 if ((msglen + 11) > modulus_len) { |
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62 return CRYPT_PK_INVALID_SIZE; |
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63 } |
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64 |
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65 if (*outlen < modulus_len) { |
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66 *outlen = modulus_len; |
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67 result = CRYPT_BUFFER_OVERFLOW; |
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68 goto bail; |
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69 } |
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70 |
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71 /* generate an octets string PS */ |
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72 ps = &out[2]; |
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73 ps_len = modulus_len - msglen - 3; |
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74 |
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75 if (block_type == LTC_PKCS_1_EME) { |
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76 /* now choose a random ps */ |
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77 if (prng_descriptor[prng_idx].read(ps, ps_len, prng) != ps_len) { |
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78 result = CRYPT_ERROR_READPRNG; |
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79 goto bail; |
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80 } |
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81 |
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82 /* transform zero bytes (if any) to non-zero random bytes */ |
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83 for (i = 0; i < ps_len; i++) { |
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84 while (ps[i] == 0) { |
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85 if (prng_descriptor[prng_idx].read(&ps[i], 1, prng) != 1) { |
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86 result = CRYPT_ERROR_READPRNG; |
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87 goto bail; |
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88 } |
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89 } |
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90 } |
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91 } else { |
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92 XMEMSET(ps, 0xFF, ps_len); |
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93 } |
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94 |
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95 /* create string of length modulus_len */ |
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96 out[0] = 0x00; |
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97 out[1] = (unsigned char)block_type; /* block_type 1 or 2 */ |
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98 out[2 + ps_len] = 0x00; |
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99 XMEMCPY(&out[2 + ps_len + 1], msg, msglen); |
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100 *outlen = modulus_len; |
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101 |
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102 result = CRYPT_OK; |
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103 bail: |
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104 return result; |
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105 } /* pkcs_1_v1_5_encode */ |
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106 |
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107 #endif /* #ifdef PKCS_1 */ |
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108 |
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109 /* $Source: /cvs/libtom/libtomcrypt/src/pk/pkcs1/pkcs_1_v1_5_encode.c,v $ */ |
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110 /* $Revision: 1.2 $ */ |
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111 /* $Date: 2006/11/01 09:12:06 $ */ |
