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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 #include "mycrypt.h" |
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12 |
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13 #ifdef MDSA |
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14 |
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15 int dsa_verify_key(dsa_key *key, int *stat) |
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16 { |
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17 mp_int tmp, tmp2; |
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18 int res, err; |
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19 |
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20 _ARGCHK(key != NULL); |
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21 _ARGCHK(stat != NULL); |
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22 |
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23 *stat = 0; |
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24 |
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25 /* first make sure key->q and key->p are prime */ |
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26 if ((err = is_prime(&key->q, &res)) != CRYPT_OK) { |
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27 return err; |
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28 } |
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29 if (res == 0) { |
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30 return CRYPT_OK; |
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31 } |
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32 |
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33 |
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34 if ((err = is_prime(&key->p, &res)) != CRYPT_OK) { |
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35 return err; |
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36 } |
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37 if (res == 0) { |
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38 return CRYPT_OK; |
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39 } |
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40 |
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41 /* now make sure that g is not -1, 0 or 1 and <p */ |
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42 if (mp_cmp_d(&key->g, 0) == MP_EQ || mp_cmp_d(&key->g, 1) == MP_EQ) { |
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43 return CRYPT_OK; |
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44 } |
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45 if ((err = mp_init_multi(&tmp, &tmp2, NULL)) != MP_OKAY) { goto error; } |
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46 if ((err = mp_sub_d(&key->p, 1, &tmp)) != MP_OKAY) { goto error; } |
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47 if (mp_cmp(&tmp, &key->g) == MP_EQ || mp_cmp(&key->g, &key->p) != MP_LT) { |
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48 err = CRYPT_OK; |
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49 goto done; |
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50 } |
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51 |
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52 /* 1 < y < p-1 */ |
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53 if (!(mp_cmp_d(&key->y, 1) == MP_GT && mp_cmp(&key->y, &tmp) == MP_LT)) { |
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54 err = CRYPT_OK; |
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55 goto done; |
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56 } |
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57 |
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58 /* now we have to make sure that g^q = 1, and that p-1/q gives 0 remainder */ |
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59 if ((err = mp_div(&tmp, &key->q, &tmp, &tmp2)) != MP_OKAY) { goto error; } |
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60 if (mp_iszero(&tmp2) != MP_YES) { |
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61 err = CRYPT_OK; |
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62 goto done; |
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63 } |
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64 |
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65 if ((err = mp_exptmod(&key->g, &key->q, &key->p, &tmp)) != MP_OKAY) { goto error; } |
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66 if (mp_cmp_d(&tmp, 1) != MP_EQ) { |
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67 err = CRYPT_OK; |
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68 goto done; |
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69 } |
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70 |
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71 /* now we have to make sure that y^q = 1, this makes sure y \in g^x mod p */ |
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72 if ((err = mp_exptmod(&key->y, &key->q, &key->p, &tmp)) != MP_OKAY) { goto error; } |
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73 if (mp_cmp_d(&tmp, 1) != MP_EQ) { |
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74 err = CRYPT_OK; |
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75 goto done; |
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76 } |
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77 |
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78 /* at this point we are out of tests ;-( */ |
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79 err = CRYPT_OK; |
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80 *stat = 1; |
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81 goto done; |
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82 error: err = mpi_to_ltc_error(err); |
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83 done : mp_clear_multi(&tmp, &tmp2, NULL); |
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84 return err; |
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85 } |
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86 #endif |
