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comparison libtomcrypt/src/pk/ecc/ecc_verify_hash.c @ 435:337c45621e81

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merge of 'a9b0496634cdd25647b65e585cc3240f3fa699ee' and 'c22be8b8f570b48e9662dac32c7b3e7148a42206'
author Matt Johnston <matt@ucc.asn.au>
date Thu, 22 Feb 2007 14:53:49 +0000
parents 0cbe8f6dbf9e
children ac2158e3e403
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434:0aaaf68e97dc 435:337c45621e81
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.com
10 */
11
12 /* Implements ECC over Z/pZ for curve y^2 = x^3 - 3x + b
13 *
14 * All curves taken from NIST recommendation paper of July 1999
15 * Available at http://csrc.nist.gov/cryptval/dss.htm
16 */
17 #include "tomcrypt.h"
18
19 /**
20 @file ecc_verify_hash.c
21 ECC Crypto, Tom St Denis
22 */
23
24 #ifdef MECC
25
26 /* verify
27 *
28 * w = s^-1 mod n
29 * u1 = xw
30 * u2 = rw
31 * X = u1*G + u2*Q
32 * v = X_x1 mod n
33 * accept if v == r
34 */
35
36 /**
37 Verify an ECC signature
38 @param sig The signature to verify
39 @param siglen The length of the signature (octets)
40 @param hash The hash (message digest) that was signed
41 @param hashlen The length of the hash (octets)
42 @param stat Result of signature, 1==valid, 0==invalid
43 @param key The corresponding public ECC key
44 @return CRYPT_OK if successful (even if the signature is not valid)
45 */
46 int ecc_verify_hash(const unsigned char *sig, unsigned long siglen,
47 const unsigned char *hash, unsigned long hashlen,
48 int *stat, ecc_key *key)
49 {
50 ecc_point *mG, *mQ;
51 void *r, *s, *v, *w, *u1, *u2, *e, *p, *m;
52 void *mp;
53 int err;
54
55 LTC_ARGCHK(sig != NULL);
56 LTC_ARGCHK(hash != NULL);
57 LTC_ARGCHK(stat != NULL);
58 LTC_ARGCHK(key != NULL);
59
60 /* default to invalid signature */
61 *stat = 0;
62 mp = NULL;
63
64 /* is the IDX valid ? */
65 if (ltc_ecc_is_valid_idx(key->idx) != 1) {
66 return CRYPT_PK_INVALID_TYPE;
67 }
68
69 /* allocate ints */
70 if ((err = mp_init_multi(&r, &s, &v, &w, &u1, &u2, &p, &e, &m, NULL)) != CRYPT_OK) {
71 return CRYPT_MEM;
72 }
73
74 /* allocate points */
75 mG = ltc_ecc_new_point();
76 mQ = ltc_ecc_new_point();
77 if (mQ == NULL || mG == NULL) {
78 err = CRYPT_MEM;
79 goto error;
80 }
81
82 /* parse header */
83 if ((err = der_decode_sequence_multi(sig, siglen,
84 LTC_ASN1_INTEGER, 1UL, r,
85 LTC_ASN1_INTEGER, 1UL, s,
86 LTC_ASN1_EOL, 0UL, NULL)) != CRYPT_OK) {
87 goto error;
88 }
89
90 /* get the order */
91 if ((err = mp_read_radix(p, (char *)key->dp->order, 16)) != CRYPT_OK) { goto error; }
92
93 /* get the modulus */
94 if ((err = mp_read_radix(m, (char *)key->dp->prime, 16)) != CRYPT_OK) { goto error; }
95
96 /* check for zero */
97 if (mp_iszero(r) || mp_iszero(s) || mp_cmp(r, p) != LTC_MP_LT || mp_cmp(s, p) != LTC_MP_LT) {
98 err = CRYPT_INVALID_PACKET;
99 goto error;
100 }
101
102 /* read hash */
103 if ((err = mp_read_unsigned_bin(e, (unsigned char *)hash, (int)hashlen)) != CRYPT_OK) { goto error; }
104
105 /* w = s^-1 mod n */
106 if ((err = mp_invmod(s, p, w)) != CRYPT_OK) { goto error; }
107
108 /* u1 = ew */
109 if ((err = mp_mulmod(e, w, p, u1)) != CRYPT_OK) { goto error; }
110
111 /* u2 = rw */
112 if ((err = mp_mulmod(r, w, p, u2)) != CRYPT_OK) { goto error; }
113
114 /* find mG and mQ */
115 if ((err = mp_read_radix(mG->x, (char *)key->dp->Gx, 16)) != CRYPT_OK) { goto error; }
116 if ((err = mp_read_radix(mG->y, (char *)key->dp->Gy, 16)) != CRYPT_OK) { goto error; }
117 if ((err = mp_set(mG->z, 1)) != CRYPT_OK) { goto error; }
118
119 if ((err = mp_copy(key->pubkey.x, mQ->x)) != CRYPT_OK) { goto error; }
120 if ((err = mp_copy(key->pubkey.y, mQ->y)) != CRYPT_OK) { goto error; }
121 if ((err = mp_copy(key->pubkey.z, mQ->z)) != CRYPT_OK) { goto error; }
122
123 /* compute u1*mG + u2*mQ = mG */
124 if (ltc_mp.ecc_mul2add == NULL) {
125 if ((err = ltc_mp.ecc_ptmul(u1, mG, mG, m, 0)) != CRYPT_OK) { goto error; }
126 if ((err = ltc_mp.ecc_ptmul(u2, mQ, mQ, m, 0)) != CRYPT_OK) { goto error; }
127
128 /* find the montgomery mp */
129 if ((err = mp_montgomery_setup(m, &mp)) != CRYPT_OK) { goto error; }
130
131 /* add them */
132 if ((err = ltc_mp.ecc_ptadd(mQ, mG, mG, m, mp)) != CRYPT_OK) { goto error; }
133
134 /* reduce */
135 if ((err = ltc_mp.ecc_map(mG, m, mp)) != CRYPT_OK) { goto error; }
136 } else {
137 /* use Shamir's trick to compute u1*mG + u2*mQ using half of the doubles */
138 if ((err = ltc_mp.ecc_mul2add(mG, u1, mQ, u2, mG, m)) != CRYPT_OK) { goto error; }
139 }
140
141 /* v = X_x1 mod n */
142 if ((err = mp_mod(mG->x, p, v)) != CRYPT_OK) { goto error; }
143
144 /* does v == r */
145 if (mp_cmp(v, r) == LTC_MP_EQ) {
146 *stat = 1;
147 }
148
149 /* clear up and return */
150 err = CRYPT_OK;
151 error:
152 ltc_ecc_del_point(mG);
153 ltc_ecc_del_point(mQ);
154 mp_clear_multi(r, s, v, w, u1, u2, p, e, m, NULL);
155 if (mp != NULL) {
156 mp_montgomery_free(mp);
157 }
158 return err;
159 }
160
161 #endif
162 /* $Source: /cvs/libtom/libtomcrypt/src/pk/ecc/ecc_verify_hash.c,v $ */
163 /* $Revision: 1.12 $ */
164 /* $Date: 2006/12/04 05:07:59 $ */
165