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annotate src/pk/dsa/dsa_verify_key.c @ 191:1c15b283127b libtomcrypt-orig

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Import of libtomcrypt 1.02 with manual path rename rearrangement etc
author Matt Johnston <matt@ucc.asn.au>
date Fri, 06 May 2005 13:23:02 +0000
parents
children 39d5d58461d6
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191
1c15b283127b Import of libtomcrypt 1.02 with manual path rename rearrangement etc
Matt Johnston <matt@ucc.asn.au>
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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 "tomcrypt.h"
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12
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13 /**
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14 @file dsa_verify_key.c
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15 DSA implementation, verify a key, Tom St Denis
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16 */
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17
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18 #ifdef MDSA
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19
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20 /**
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21 Verify a DSA key for validity
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22 @param key The key to verify
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23 @param stat [out] Result of test, 1==valid, 0==invalid
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24 @return CRYPT_OK if successful
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25 */
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26 int dsa_verify_key(dsa_key *key, int *stat)
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27 {
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28 mp_int tmp, tmp2;
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29 int res, err;
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30
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31 LTC_ARGCHK(key != NULL);
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32 LTC_ARGCHK(stat != NULL);
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33
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34 /* default to an invalid key */
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35 *stat = 0;
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36
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37 /* first make sure key->q and key->p are prime */
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38 if ((err = is_prime(&key->q, &res)) != CRYPT_OK) {
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39 return err;
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40 }
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41 if (res == 0) {
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42 return CRYPT_OK;
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43 }
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44
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45
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46 if ((err = is_prime(&key->p, &res)) != CRYPT_OK) {
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47 return err;
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48 }
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49 if (res == 0) {
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50 return CRYPT_OK;
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51 }
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52
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53 /* now make sure that g is not -1, 0 or 1 and <p */
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54 if (mp_cmp_d(&key->g, 0) == MP_EQ || mp_cmp_d(&key->g, 1) == MP_EQ) {
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55 return CRYPT_OK;
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56 }
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57 if ((err = mp_init_multi(&tmp, &tmp2, NULL)) != MP_OKAY) { goto error; }
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58 if ((err = mp_sub_d(&key->p, 1, &tmp)) != MP_OKAY) { goto error; }
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59 if (mp_cmp(&tmp, &key->g) == MP_EQ || mp_cmp(&key->g, &key->p) != MP_LT) {
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60 err = CRYPT_OK;
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61 goto done;
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62 }
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63
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64 /* 1 < y < p-1 */
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65 if (!(mp_cmp_d(&key->y, 1) == MP_GT && mp_cmp(&key->y, &tmp) == MP_LT)) {
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66 err = CRYPT_OK;
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67 goto done;
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68 }
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69
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70 /* now we have to make sure that g^q = 1, and that p-1/q gives 0 remainder */
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71 if ((err = mp_div(&tmp, &key->q, &tmp, &tmp2)) != MP_OKAY) { goto error; }
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72 if (mp_iszero(&tmp2) != MP_YES) {
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73 err = CRYPT_OK;
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74 goto done;
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75 }
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76
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77 if ((err = mp_exptmod(&key->g, &key->q, &key->p, &tmp)) != MP_OKAY) { goto error; }
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78 if (mp_cmp_d(&tmp, 1) != MP_EQ) {
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79 err = CRYPT_OK;
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80 goto done;
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81 }
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82
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83 /* now we have to make sure that y^q = 1, this makes sure y \in g^x mod p */
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84 if ((err = mp_exptmod(&key->y, &key->q, &key->p, &tmp)) != MP_OKAY) { goto error; }
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85 if (mp_cmp_d(&tmp, 1) != MP_EQ) {
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86 err = CRYPT_OK;
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87 goto done;
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88 }
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89
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90 /* at this point we are out of tests ;-( */
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91 err = CRYPT_OK;
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92 *stat = 1;
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93 goto done;
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94 error: err = mpi_to_ltc_error(err);
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95 done : mp_clear_multi(&tmp, &tmp2, NULL);
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96 return err;
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97 }
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98 #endif