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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 |
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12 /* RSA Code by Tom St Denis */ |
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13 #include "mycrypt.h" |
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14 |
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15 #ifdef MRSA |
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16 |
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143
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17 /* compute an RSA modular exponentiation */ |
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15
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18 int rsa_exptmod(const unsigned char *in, unsigned long inlen, |
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19 unsigned char *out, unsigned long *outlen, int which, |
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20 prng_state *prng, int prng_idx, |
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3
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21 rsa_key *key) |
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22 { |
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15
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23 mp_int tmp, tmpa, tmpb; |
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3
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24 unsigned long x; |
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15
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25 int err; |
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26 |
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27 _ARGCHK(in != NULL); |
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28 _ARGCHK(out != NULL); |
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29 _ARGCHK(outlen != NULL); |
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30 _ARGCHK(key != NULL); |
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15
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31 |
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143
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32 /* valid prng? */ |
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15
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33 if ((err = prng_is_valid(prng_idx)) != CRYPT_OK) { |
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34 return err; |
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35 } |
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36 |
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143
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37 /* is the key of the right type for the operation? */ |
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38 if (which == PK_PRIVATE && (key->type != PK_PRIVATE)) { |
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39 return CRYPT_PK_NOT_PRIVATE; |
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40 } |
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41 |
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42 /* must be a private or public operation */ |
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43 if (which != PK_PRIVATE && which != PK_PUBLIC) { |
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44 return CRYPT_PK_INVALID_TYPE; |
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45 } |
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46 |
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47 /* init and copy into tmp */ |
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143
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48 if ((err = mp_init_multi(&tmp, &tmpa, &tmpb, NULL)) != MP_OKAY) { return mpi_to_ltc_error(err); } |
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49 if ((err = mp_read_unsigned_bin(&tmp, (unsigned char *)in, (int)inlen)) != MP_OKAY) { goto error; } |
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50 |
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51 /* sanity check on the input */ |
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52 if (mp_cmp(&key->N, &tmp) == MP_LT) { |
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53 err = CRYPT_PK_INVALID_SIZE; |
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54 goto done; |
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55 } |
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56 |
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57 /* are we using the private exponent and is the key optimized? */ |
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143
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58 if (which == PK_PRIVATE) { |
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3
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59 /* tmpa = tmp^dP mod p */ |
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15
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60 if ((err = tim_exptmod(prng, prng_idx, &tmp, &key->e, &key->dP, &key->p, &tmpa)) != MP_OKAY) { goto error; } |
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61 |
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62 /* tmpb = tmp^dQ mod q */ |
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63 if ((err = tim_exptmod(prng, prng_idx, &tmp, &key->e, &key->dQ, &key->q, &tmpb)) != MP_OKAY) { goto error; } |
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64 |
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143
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65 /* tmp = (tmpa - tmpb) * qInv (mod p) */ |
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66 if ((err = mp_sub(&tmpa, &tmpb, &tmp)) != MP_OKAY) { goto error; } |
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67 if ((err = mp_mulmod(&tmp, &key->qP, &key->p, &tmp)) != MP_OKAY) { goto error; } |
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68 |
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69 /* tmp = tmpb + q * tmp */ |
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70 if ((err = mp_mul(&tmp, &key->q, &tmp)) != MP_OKAY) { goto error; } |
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71 if ((err = mp_add(&tmp, &tmpb, &tmp)) != MP_OKAY) { goto error; } |
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3
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72 } else { |
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73 /* exptmod it */ |
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143
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74 if ((err = mp_exptmod(&tmp, &key->e, &key->N, &tmp)) != MP_OKAY) { goto error; } |
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3
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75 } |
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76 |
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77 /* read it back */ |
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15
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78 x = (unsigned long)mp_unsigned_bin_size(&key->N); |
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3
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79 if (x > *outlen) { |
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80 err = CRYPT_BUFFER_OVERFLOW; |
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81 goto done; |
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82 } |
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83 *outlen = x; |
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84 |
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85 /* convert it */ |
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15
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86 zeromem(out, x); |
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87 if ((err = mp_to_unsigned_bin(&tmp, out+(x-mp_unsigned_bin_size(&tmp)))) != MP_OKAY) { goto error; } |
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88 |
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89 /* clean up and return */ |
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90 err = CRYPT_OK; |
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91 goto done; |
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92 error: |
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93 err = mpi_to_ltc_error(err); |
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94 done: |
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95 mp_clear_multi(&tmp, &tmpa, &tmpb, NULL); |
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96 return err; |
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97 } |
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98 |
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99 #endif |
