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comparison libtomcrypt/src/pk/dsa/dsa_verify_hash.c @ 285:1b9e69c058d2

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propagate from branch 'au.asn.ucc.matt.ltc.dropbear' (head 20dccfc09627970a312d77fb41dc2970b62689c3) to branch 'au.asn.ucc.matt.dropbear' (head fdf4a7a3b97ae5046139915de7e40399cceb2c01)
author Matt Johnston <matt@ucc.asn.au>
date Wed, 08 Mar 2006 13:23:58 +0000
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children 0cbe8f6dbf9e
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281:997e6f7dc01e 285:1b9e69c058d2
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 r DSA "r" parameter
24 @param s DSA "s" parameter
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_raw( mp_int *r, mp_int *s,
32 const unsigned char *hash, unsigned long hashlen,
33 int *stat, dsa_key *key)
34 {
35 mp_int w, v, u1, u2;
36 int err;
37
38 LTC_ARGCHK(r != NULL);
39 LTC_ARGCHK(s != 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(&w, &v, &u1, &u2, NULL)) != MP_OKAY) {
48 return mpi_to_ltc_error(err);
49 }
50
51 /* neither r or s can be null or >q*/
52 if (mp_iszero(r) == MP_YES || mp_iszero(s) == MP_YES || mp_cmp(r, &key->q) != MP_LT || mp_cmp(s, &key->q) != MP_LT) {
53 err = CRYPT_INVALID_PACKET;
54 goto done;
55 }
56
57 /* w = 1/s mod q */
58 if ((err = mp_invmod(s, &key->q, &w)) != MP_OKAY) { goto error; }
59
60 /* u1 = m * w mod q */
61 if ((err = mp_read_unsigned_bin(&u1, (unsigned char *)hash, hashlen)) != MP_OKAY) { goto error; }
62 if ((err = mp_mulmod(&u1, &w, &key->q, &u1)) != MP_OKAY) { goto error; }
63
64 /* u2 = r*w mod q */
65 if ((err = mp_mulmod(r, &w, &key->q, &u2)) != MP_OKAY) { goto error; }
66
67 /* v = g^u1 * y^u2 mod p mod q */
68 if ((err = mp_exptmod(&key->g, &u1, &key->p, &u1)) != MP_OKAY) { goto error; }
69 if ((err = mp_exptmod(&key->y, &u2, &key->p, &u2)) != MP_OKAY) { goto error; }
70 if ((err = mp_mulmod(&u1, &u2, &key->p, &v)) != MP_OKAY) { goto error; }
71 if ((err = mp_mod(&v, &key->q, &v)) != MP_OKAY) { goto error; }
72
73 /* if r = v then we're set */
74 if (mp_cmp(r, &v) == MP_EQ) {
75 *stat = 1;
76 }
77
78 err = CRYPT_OK;
79 goto done;
80
81 error : err = mpi_to_ltc_error(err);
82 done : mp_clear_multi(&w, &v, &u1, &u2, NULL);
83 return err;
84 }
85
86 /**
87 Verify a DSA signature
88 @param sig The signature
89 @param siglen The length of the signature (octets)
90 @param hash The hash that was signed
91 @param hashlen The length of the hash that was signed
92 @param stat [out] The result of the signature verification, 1==valid, 0==invalid
93 @param key The corresponding public DH key
94 @return CRYPT_OK if successful (even if the signature is invalid)
95 */
96 int dsa_verify_hash(const unsigned char *sig, unsigned long siglen,
97 const unsigned char *hash, unsigned long hashlen,
98 int *stat, dsa_key *key)
99 {
100 int err;
101 mp_int r, s;
102
103 if ((err = mp_init_multi(&r, &s, NULL)) != CRYPT_OK) {
104 return CRYPT_MEM;
105 }
106
107 /* decode the sequence */
108 if ((err = der_decode_sequence_multi(sig, siglen,
109 LTC_ASN1_INTEGER, 1UL, &r,
110 LTC_ASN1_INTEGER, 1UL, &s,
111 LTC_ASN1_EOL, 0UL, NULL)) != CRYPT_OK) {
112 goto LBL_ERR;
113 }
114
115 /* do the op */
116 err = dsa_verify_hash_raw(&r, &s, hash, hashlen, stat, key);
117
118 LBL_ERR:
119 mp_clear_multi(&r, &s, NULL);
120 return err;
121 }
122
123 #endif
124
125
126 /* $Source: /cvs/libtom/libtomcrypt/src/pk/dsa/dsa_verify_hash.c,v $ */
127 /* $Revision: 1.8 $ */
128 /* $Date: 2005/05/15 21:48:59 $ */