1 // SPDX-License-Identifier: BSD-2-Clause
2 /* LibTomCrypt, modular cryptographic library -- Tom St Denis
3 *
4 * LibTomCrypt is a library that provides various cryptographic
5 * algorithms in a highly modular and flexible manner.
6 *
7 * The library is free for all purposes without any express
8 * guarantee it works.
9 */
10 #include "tomcrypt_private.h"
11
12 /**
13 @file dsa_verify_hash.c
14 DSA implementation, verify a signature, Tom St Denis
15 */
16
17
18 #ifdef LTC_MDSA
19
20 /**
21 Verify a DSA signature
22 @param r DSA "r" parameter
23 @param s DSA "s" parameter
24 @param hash The hash that was signed
25 @param hashlen The length of the hash that was signed
26 @param stat [out] The result of the signature verification, 1==valid, 0==invalid
27 @param key The corresponding public DSA key
28 @return CRYPT_OK if successful (even if the signature is invalid)
29 */
dsa_verify_hash_raw(void * r,void * s,const unsigned char * hash,unsigned long hashlen,int * stat,const dsa_key * key)30 int dsa_verify_hash_raw( void *r, void *s,
31 const unsigned char *hash, unsigned long hashlen,
32 int *stat, const dsa_key *key)
33 {
34 void *w, *v, *u1, *u2;
35 int err;
36
37 LTC_ARGCHK(r != NULL);
38 LTC_ARGCHK(s != NULL);
39 LTC_ARGCHK(stat != NULL);
40 LTC_ARGCHK(key != NULL);
41
42 /* default to invalid signature */
43 *stat = 0;
44
45 /* init our variables */
46 if ((err = mp_init_multi(&w, &v, &u1, &u2, NULL)) != CRYPT_OK) {
47 return err;
48 }
49
50 /* neither r or s can be null or >q*/
51 if (mp_cmp_d(r, 0) != LTC_MP_GT || mp_cmp_d(s, 0) != LTC_MP_GT || mp_cmp(r, key->q) != LTC_MP_LT || mp_cmp(s, key->q) != LTC_MP_LT) {
52 err = CRYPT_INVALID_PACKET;
53 goto error;
54 }
55
56 /* FIPS 186-4 4.7: use leftmost min(bitlen(q), bitlen(hash)) bits of 'hash' */
57 hashlen = MIN(hashlen, (unsigned long)(key->qord));
58
59 /* w = 1/s mod q */
60 if ((err = mp_invmod(s, key->q, w)) != CRYPT_OK) { goto error; }
61
62 /* u1 = m * w mod q */
63 if ((err = mp_read_unsigned_bin(u1, (unsigned char *)hash, hashlen)) != CRYPT_OK) { goto error; }
64 if ((err = mp_mulmod(u1, w, key->q, u1)) != CRYPT_OK) { goto error; }
65
66 /* u2 = r*w mod q */
67 if ((err = mp_mulmod(r, w, key->q, u2)) != CRYPT_OK) { goto error; }
68
69 /* v = g^u1 * y^u2 mod p mod q */
70 if ((err = mp_exptmod(key->g, u1, key->p, u1)) != CRYPT_OK) { goto error; }
71 if ((err = mp_exptmod(key->y, u2, key->p, u2)) != CRYPT_OK) { goto error; }
72 if ((err = mp_mulmod(u1, u2, key->p, v)) != CRYPT_OK) { goto error; }
73 if ((err = mp_mod(v, key->q, v)) != CRYPT_OK) { goto error; }
74
75 /* if r = v then we're set */
76 if (mp_cmp(r, v) == LTC_MP_EQ) {
77 *stat = 1;
78 }
79
80 err = CRYPT_OK;
81 error:
82 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 DSA key
94 @return CRYPT_OK if successful (even if the signature is invalid)
95 */
dsa_verify_hash(const unsigned char * sig,unsigned long siglen,const unsigned char * hash,unsigned long hashlen,int * stat,const dsa_key * key)96 int dsa_verify_hash(const unsigned char *sig, unsigned long siglen,
97 const unsigned char *hash, unsigned long hashlen,
98 int *stat, const dsa_key *key)
99 {
100 int err;
101 void *r, *s;
102 ltc_asn1_list sig_seq[2];
103 unsigned long reallen = 0;
104
105 LTC_ARGCHK(stat != NULL);
106 *stat = 0; /* must be set before the first return */
107
108 if ((err = mp_init_multi(&r, &s, NULL)) != CRYPT_OK) {
109 return err;
110 }
111
112 LTC_SET_ASN1(sig_seq, 0, LTC_ASN1_INTEGER, r, 1UL);
113 LTC_SET_ASN1(sig_seq, 1, LTC_ASN1_INTEGER, s, 1UL);
114
115 err = der_decode_sequence_strict(sig, siglen, sig_seq, 2);
116 if (err != CRYPT_OK) {
117 goto LBL_ERR;
118 }
119
120 err = der_length_sequence(sig_seq, 2, &reallen);
121 if (err != CRYPT_OK || reallen != siglen) {
122 goto LBL_ERR;
123 }
124
125 /* do the op */
126 err = dsa_verify_hash_raw(r, s, hash, hashlen, stat, key);
127
128 LBL_ERR:
129 mp_clear_multi(r, s, NULL);
130 return err;
131 }
132
133 #endif
134
135
136 /* ref: $Format:%D$ */
137 /* git commit: $Format:%H$ */
138 /* commit time: $Format:%ai$ */
139