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comparison dsa_verify_key.c @ 3:7faae8f46238 libtomcrypt-orig

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Branch renaming
author Matt Johnston <matt@ucc.asn.au>
date Mon, 31 May 2004 18:25:41 +0000
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-1:000000000000 3:7faae8f46238
1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis
2 *
3 * LibTomCrypt is a library that provides various cryptographic
4 * algorithms in a highly modular and flexible manner.
5 *
6 * The library is free for all purposes without any express
7 * guarantee it works.
8 *
9 * Tom St Denis, [email protected], http://libtomcrypt.org
10 */
11 #include "mycrypt.h"
12
13 #ifdef MDSA
14
15 int dsa_verify_key(dsa_key *key, int *stat)
16 {
17 mp_int tmp, tmp2;
18 int res, err;
19
20 _ARGCHK(key != NULL);
21 _ARGCHK(stat != NULL);
22
23 *stat = 0;
24
25 /* first make sure key->q and key->p are prime */
26 if ((err = is_prime(&key->q, &res)) != CRYPT_OK) {
27 return err;
28 }
29 if (res == 0) {
30 return CRYPT_OK;
31 }
32
33
34 if ((err = is_prime(&key->p, &res)) != CRYPT_OK) {
35 return err;
36 }
37 if (res == 0) {
38 return CRYPT_OK;
39 }
40
41 /* now make sure that g is not -1, 0 or 1 and <p */
42 if (mp_cmp_d(&key->g, 0) == MP_EQ || mp_cmp_d(&key->g, 1) == MP_EQ) {
43 return CRYPT_OK;
44 }
45 if ((err = mp_init_multi(&tmp, &tmp2, NULL)) != MP_OKAY) { goto error; }
46 if ((err = mp_sub_d(&key->p, 1, &tmp)) != MP_OKAY) { goto error; }
47 if (mp_cmp(&tmp, &key->g) == MP_EQ || mp_cmp(&key->g, &key->p) != MP_LT) {
48 err = CRYPT_OK;
49 goto done;
50 }
51
52 /* 1 < y < p-1 */
53 if (!(mp_cmp_d(&key->y, 1) == MP_GT && mp_cmp(&key->y, &tmp) == MP_LT)) {
54 err = CRYPT_OK;
55 goto done;
56 }
57
58 /* now we have to make sure that g^q = 1, and that p-1/q gives 0 remainder */
59 if ((err = mp_div(&tmp, &key->q, &tmp, &tmp2)) != MP_OKAY) { goto error; }
60 if (mp_iszero(&tmp2) != MP_YES) {
61 err = CRYPT_OK;
62 goto done;
63 }
64
65 if ((err = mp_exptmod(&key->g, &key->q, &key->p, &tmp)) != MP_OKAY) { goto error; }
66 if (mp_cmp_d(&tmp, 1) != MP_EQ) {
67 err = CRYPT_OK;
68 goto done;
69 }
70
71 /* now we have to make sure that y^q = 1, this makes sure y \in g^x mod p */
72 if ((err = mp_exptmod(&key->y, &key->q, &key->p, &tmp)) != MP_OKAY) { goto error; }
73 if (mp_cmp_d(&tmp, 1) != MP_EQ) {
74 err = CRYPT_OK;
75 goto done;
76 }
77
78 /* at this point we are out of tests ;-( */
79 err = CRYPT_OK;
80 *stat = 1;
81 goto done;
82 error: err = mpi_to_ltc_error(err);
83 done : mp_clear_multi(&tmp, &tmp2, NULL);
84 return err;
85 }
86 #endif