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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 katja_exptmod.c |
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15 Katja PKCS-style exptmod, Tom St Denis |
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16 */ |
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17 |
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18 #ifdef MKAT |
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19 |
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20 /** |
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21 Compute an RSA modular exponentiation |
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22 @param in The input data to send into RSA |
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23 @param inlen The length of the input (octets) |
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24 @param out [out] The destination |
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25 @param outlen [in/out] The max size and resulting size of the output |
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26 @param which Which exponent to use, e.g. PK_PRIVATE or PK_PUBLIC |
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27 @param key The RSA key to use |
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28 @return CRYPT_OK if successful |
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29 */ |
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30 int katja_exptmod(const unsigned char *in, unsigned long inlen, |
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31 unsigned char *out, unsigned long *outlen, int which, |
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32 katja_key *key) |
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33 { |
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34 void *tmp, *tmpa, *tmpb; |
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35 unsigned long x; |
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36 int err; |
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37 |
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38 LTC_ARGCHK(in != NULL); |
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39 LTC_ARGCHK(out != NULL); |
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40 LTC_ARGCHK(outlen != NULL); |
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41 LTC_ARGCHK(key != NULL); |
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42 |
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43 /* is the key of the right type for the operation? */ |
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44 if (which == PK_PRIVATE && (key->type != PK_PRIVATE)) { |
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45 return CRYPT_PK_NOT_PRIVATE; |
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46 } |
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47 |
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48 /* must be a private or public operation */ |
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49 if (which != PK_PRIVATE && which != PK_PUBLIC) { |
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50 return CRYPT_PK_INVALID_TYPE; |
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51 } |
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52 |
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53 /* init and copy into tmp */ |
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54 if ((err = mp_init_multi(&tmp, &tmpa, &tmpb, NULL)) != CRYPT_OK) { return err; } |
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55 if ((err = mp_read_unsigned_bin(tmp, (unsigned char *)in, (int)inlen)) != CRYPT_OK) { goto error; } |
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56 |
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57 /* sanity check on the input */ |
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58 if (mp_cmp(key->N, tmp) == LTC_MP_LT) { |
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59 err = CRYPT_PK_INVALID_SIZE; |
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60 goto done; |
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61 } |
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62 |
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63 /* are we using the private exponent and is the key optimized? */ |
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64 if (which == PK_PRIVATE) { |
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65 /* tmpa = tmp^dP mod p */ |
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66 if ((err = mp_exptmod(tmp, key->dP, key->p, tmpa)) != CRYPT_OK) { goto error; } |
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67 |
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68 /* tmpb = tmp^dQ mod q */ |
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69 if ((err = mp_exptmod(tmp, key->dQ, key->q, tmpb)) != CRYPT_OK) { goto error; } |
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70 |
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71 /* tmp = (tmpa - tmpb) * qInv (mod p) */ |
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72 if ((err = mp_sub(tmpa, tmpb, tmp)) != CRYPT_OK) { goto error; } |
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73 if ((err = mp_mulmod(tmp, key->qP, key->p, tmp)) != CRYPT_OK) { goto error; } |
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74 |
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75 /* tmp = tmpb + q * tmp */ |
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76 if ((err = mp_mul(tmp, key->q, tmp)) != CRYPT_OK) { goto error; } |
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77 if ((err = mp_add(tmp, tmpb, tmp)) != CRYPT_OK) { goto error; } |
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78 } else { |
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79 /* exptmod it */ |
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80 if ((err = mp_exptmod(tmp, key->N, key->N, tmp)) != CRYPT_OK) { goto error; } |
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81 } |
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82 |
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83 /* read it back */ |
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84 x = (unsigned long)mp_unsigned_bin_size(key->N); |
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85 if (x > *outlen) { |
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86 *outlen = x; |
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87 err = CRYPT_BUFFER_OVERFLOW; |
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88 goto done; |
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89 } |
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90 |
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91 /* this should never happen ... */ |
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92 if (mp_unsigned_bin_size(tmp) > mp_unsigned_bin_size(key->N)) { |
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93 err = CRYPT_ERROR; |
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94 goto done; |
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95 } |
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96 *outlen = x; |
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97 |
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98 /* convert it */ |
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99 zeromem(out, x); |
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100 if ((err = mp_to_unsigned_bin(tmp, out+(x-mp_unsigned_bin_size(tmp)))) != CRYPT_OK) { goto error; } |
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101 |
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102 /* clean up and return */ |
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103 err = CRYPT_OK; |
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104 goto done; |
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105 error: |
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106 done: |
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107 mp_clear_multi(tmp, tmpa, tmpb, NULL); |
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108 return err; |
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109 } |
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110 |
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111 #endif |
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112 |
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113 /* $Source: /cvs/libtom/libtomcrypt/src/pk/katja/katja_exptmod.c,v $ */ |
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114 /* $Revision: 1.5 $ */ |
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115 /* $Date: 2006/06/16 21:53:41 $ */ |
