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comparison src/pk/dsa/dsa_verify_hash.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
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children 39d5d58461d6
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143:5d99163f7e32 191:1c15b283127b
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 "tomcrypt.h"
12
13 /**
14 @file dsa_verify_hash.c
15 DSA implementation, verify a signature, Tom St Denis
16 */
17
18
19 #ifdef MDSA
20
21 /**
22 Verify a DSA signature
23 @param sig The signature
24 @param siglen The length of the signature (octets)
25 @param hash The hash that was signed
26 @param hashlen The length of the hash that was signed
27 @param stat [out] The result of the signature verification, 1==valid, 0==invalid
28 @param key The corresponding public DH key
29 @return CRYPT_OK if successful (even if the signature is invalid)
30 */
31 int dsa_verify_hash(const unsigned char *sig, unsigned long siglen,
32 const unsigned char *hash, unsigned long hashlen,
33 int *stat, dsa_key *key)
34 {
35 mp_int r, s, w, v, u1, u2;
36 int err;
37
38 LTC_ARGCHK(sig != NULL);
39 LTC_ARGCHK(hash != NULL);
40 LTC_ARGCHK(stat != NULL);
41 LTC_ARGCHK(key != NULL);
42
43 /* default to invalid signature */
44 *stat = 0;
45
46 /* init our variables */
47 if ((err = mp_init_multi(&r, &s, &w, &v, &u1, &u2, NULL)) != MP_OKAY) {
48 return mpi_to_ltc_error(err);
49 }
50
51 /* read in r followed by s */
52 if ((err = der_get_multi_integer(sig, &siglen, &r, &s, NULL)) != CRYPT_OK) { goto done; }
53
54 /* neither r or s can be null */
55 if (mp_iszero(&r) == MP_YES || mp_iszero(&s) == MP_YES) {
56 err = CRYPT_INVALID_PACKET;
57 goto done;
58 }
59
60 /* w = 1/s mod q */
61 if ((err = mp_invmod(&s, &key->q, &w)) != MP_OKAY) { goto error; }
62
63 /* u1 = m * w mod q */
64 if ((err = mp_read_unsigned_bin(&u1, (unsigned char *)hash, hashlen)) != MP_OKAY) { goto error; }
65 if ((err = mp_mulmod(&u1, &w, &key->q, &u1)) != MP_OKAY) { goto error; }
66
67 /* u2 = r*w mod q */
68 if ((err = mp_mulmod(&r, &w, &key->q, &u2)) != MP_OKAY) { goto error; }
69
70 /* v = g^u1 * y^u2 mod p mod q */
71 if ((err = mp_exptmod(&key->g, &u1, &key->p, &u1)) != MP_OKAY) { goto error; }
72 if ((err = mp_exptmod(&key->y, &u2, &key->p, &u2)) != MP_OKAY) { goto error; }
73 if ((err = mp_mulmod(&u1, &u2, &key->p, &v)) != MP_OKAY) { goto error; }
74 if ((err = mp_mod(&v, &key->q, &v)) != MP_OKAY) { goto error; }
75
76 /* if r = v then we're set */
77 if (mp_cmp(&r, &v) == MP_EQ) {
78 *stat = 1;
79 }
80
81 err = CRYPT_OK;
82 goto done;
83
84 error : err = mpi_to_ltc_error(err);
85 done : mp_clear_multi(&r, &s, &w, &v, &u1, &u2, NULL);
86 return err;
87 }
88
89 #endif
90