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annotate dsa_verify_key.c @ 0:d7da3b1e1540 libtomcrypt

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put back the 0.95 makefile which was inadvertently merged over
author Matt Johnston <matt@ucc.asn.au>
date Mon, 31 May 2004 18:21:40 +0000
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d7da3b1e1540 put back the 0.95 makefile which was inadvertently merged over
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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