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
11 #include "tomcrypt_private.h"
12
13 #ifdef LTC_MECC
14
15 /**
16 @file ecc_verify_hash.c
17 ECC Crypto, Tom St Denis
18 */
19
20 /**
21 Verify an ECC signature in RFC7518 format
22 @param sig The signature to verify
23 @param siglen The length of the signature (octets)
24 @param hash The hash (message digest) that was signed
25 @param hashlen The length of the hash (octets)
26 @param sigformat The format of the signature (ecc_signature_type)
27 @param stat Result of signature, 1==valid, 0==invalid
28 @param key The corresponding public ECC key
29 @return CRYPT_OK if successful (even if the signature is not valid)
30 */
ecc_verify_hash_ex(const unsigned char * sig,unsigned long siglen,const unsigned char * hash,unsigned long hashlen,ecc_signature_type sigformat,int * stat,const ecc_key * key)31 int ecc_verify_hash_ex(const unsigned char *sig, unsigned long siglen,
32 const unsigned char *hash, unsigned long hashlen,
33 ecc_signature_type sigformat, int *stat, const ecc_key *key)
34 {
35 ecc_point *mG = NULL, *mQ = NULL;
36 void *r, *s, *v, *w, *u1, *u2, *e, *p, *m, *a, *a_plus3;
37 void *mu = NULL, *ma = NULL;
38 void *mp = NULL;
39 int err;
40 unsigned long pbits, pbytes, i, shift_right;
41 unsigned char ch, buf[MAXBLOCKSIZE];
42
43 LTC_ARGCHK(sig != NULL);
44 LTC_ARGCHK(hash != NULL);
45 LTC_ARGCHK(stat != NULL);
46 LTC_ARGCHK(key != NULL);
47
48 /* default to invalid signature */
49 *stat = 0;
50
51 /* allocate ints */
52 if ((err = mp_init_multi(&r, &s, &v, &w, &u1, &u2, &e, &a_plus3, NULL)) != CRYPT_OK) {
53 return err;
54 }
55
56 p = key->dp.order;
57 m = key->dp.prime;
58 a = key->dp.A;
59 if ((err = mp_add_d(a, 3, a_plus3)) != CRYPT_OK) {
60 goto error;
61 }
62
63 /* allocate points */
64 mG = ltc_ecc_new_point();
65 mQ = ltc_ecc_new_point();
66 if (mQ == NULL || mG == NULL) {
67 err = CRYPT_MEM;
68 goto error;
69 }
70
71 if (sigformat == LTC_ECCSIG_ANSIX962) {
72 /* ANSI X9.62 format - ASN.1 encoded SEQUENCE{ INTEGER(r), INTEGER(s) } */
73 if ((err = der_decode_sequence_multi_ex(sig, siglen, LTC_DER_SEQ_SEQUENCE | LTC_DER_SEQ_STRICT,
74 LTC_ASN1_INTEGER, 1UL, r,
75 LTC_ASN1_INTEGER, 1UL, s,
76 LTC_ASN1_EOL, 0UL, NULL)) != CRYPT_OK) { goto error; }
77 }
78 else if (sigformat == LTC_ECCSIG_RFC7518) {
79 /* RFC7518 format - raw (r,s) */
80 i = mp_unsigned_bin_size(key->dp.order);
81 if (siglen != (2 * i)) {
82 err = CRYPT_INVALID_PACKET;
83 goto error;
84 }
85 if ((err = mp_read_unsigned_bin(r, (unsigned char *)sig, i)) != CRYPT_OK) { goto error; }
86 if ((err = mp_read_unsigned_bin(s, (unsigned char *)sig+i, i)) != CRYPT_OK) { goto error; }
87 }
88 else if (sigformat == LTC_ECCSIG_ETH27) {
89 /* Ethereum (v,r,s) format */
90 if (pk_oid_cmp_with_ulong("1.3.132.0.10", key->dp.oid, key->dp.oidlen) != CRYPT_OK) {
91 /* Only valid for secp256k1 - OID 1.3.132.0.10 */
92 err = CRYPT_ERROR; goto error;
93 }
94 if (siglen != 65) { /* Only secp256k1 curves use this format, so must be 65 bytes long */
95 err = CRYPT_INVALID_PACKET;
96 goto error;
97 }
98 if ((err = mp_read_unsigned_bin(r, (unsigned char *)sig, 32)) != CRYPT_OK) { goto error; }
99 if ((err = mp_read_unsigned_bin(s, (unsigned char *)sig+32, 32)) != CRYPT_OK) { goto error; }
100 }
101 #ifdef LTC_SSH
102 else if (sigformat == LTC_ECCSIG_RFC5656) {
103 char name[64], name2[64];
104 unsigned long namelen = sizeof(name2);
105
106 /* Decode as SSH data sequence, per RFC4251 */
107 if ((err = ssh_decode_sequence_multi(sig, siglen,
108 LTC_SSHDATA_STRING, name, 64,
109 LTC_SSHDATA_MPINT, r,
110 LTC_SSHDATA_MPINT, s,
111 LTC_SSHDATA_EOL, NULL)) != CRYPT_OK) { goto error; }
112
113
114 /* Check curve matches identifier string */
115 if ((err = ecc_ssh_ecdsa_encode_name(name2, &namelen, key)) != CRYPT_OK) { goto error; }
116 if (XSTRCMP(name,name2) != 0) {
117 err = CRYPT_INVALID_ARG;
118 goto error;
119 }
120 }
121 #endif
122 else {
123 /* Unknown signature format */
124 err = CRYPT_ERROR;
125 goto error;
126 }
127
128 /* check for zero */
129 if (mp_cmp_d(r, 0) != LTC_MP_GT || mp_cmp_d(s, 0) != LTC_MP_GT ||
130 mp_cmp(r, p) != LTC_MP_LT || mp_cmp(s, p) != LTC_MP_LT) {
131 err = CRYPT_INVALID_PACKET;
132 goto error;
133 }
134
135 /* read hash - truncate if needed */
136 pbits = mp_count_bits(p);
137 pbytes = (pbits+7) >> 3;
138 if (pbits > hashlen*8) {
139 if ((err = mp_read_unsigned_bin(e, (unsigned char *)hash, hashlen)) != CRYPT_OK) { goto error; }
140 }
141 else if (pbits % 8 == 0) {
142 if ((err = mp_read_unsigned_bin(e, (unsigned char *)hash, pbytes)) != CRYPT_OK) { goto error; }
143 }
144 else {
145 shift_right = 8 - pbits % 8;
146 for (i=0, ch=0; i<pbytes; i++) {
147 buf[i] = ch;
148 ch = (hash[i] << (8-shift_right));
149 buf[i] = buf[i] ^ (hash[i] >> shift_right);
150 }
151 if ((err = mp_read_unsigned_bin(e, (unsigned char *)buf, pbytes)) != CRYPT_OK) { goto error; }
152 }
153
154 /* w = s^-1 mod n */
155 if ((err = mp_invmod(s, p, w)) != CRYPT_OK) { goto error; }
156
157 /* u1 = ew */
158 if ((err = mp_mulmod(e, w, p, u1)) != CRYPT_OK) { goto error; }
159
160 /* u2 = rw */
161 if ((err = mp_mulmod(r, w, p, u2)) != CRYPT_OK) { goto error; }
162
163 /* find mG and mQ */
164 if ((err = ltc_ecc_copy_point(&key->dp.base, mG)) != CRYPT_OK) { goto error; }
165 if ((err = ltc_ecc_copy_point(&key->pubkey, mQ)) != CRYPT_OK) { goto error; }
166
167 /* find the montgomery mp */
168 if ((err = mp_montgomery_setup(m, &mp)) != CRYPT_OK) { goto error; }
169
170 /* for curves with a == -3 keep ma == NULL */
171 if (mp_cmp(a_plus3, m) != LTC_MP_EQ) {
172 if ((err = mp_init_multi(&mu, &ma, NULL)) != CRYPT_OK) { goto error; }
173 if ((err = mp_montgomery_normalization(mu, m)) != CRYPT_OK) { goto error; }
174 if ((err = mp_mulmod(a, mu, m, ma)) != CRYPT_OK) { goto error; }
175 }
176
177 /* compute u1*mG + u2*mQ = mG */
178 if (ltc_mp.ecc_mul2add == NULL) {
179 if ((err = ltc_mp.ecc_ptmul(u1, mG, mG, a, m, 0)) != CRYPT_OK) { goto error; }
180 if ((err = ltc_mp.ecc_ptmul(u2, mQ, mQ, a, m, 0)) != CRYPT_OK) { goto error; }
181
182 /* add them */
183 if ((err = ltc_mp.ecc_ptadd(mQ, mG, mG, ma, m, mp)) != CRYPT_OK) { goto error; }
184
185 /* reduce */
186 if ((err = ltc_mp.ecc_map(mG, m, mp)) != CRYPT_OK) { goto error; }
187 } else {
188 /* use Shamir's trick to compute u1*mG + u2*mQ using half of the doubles */
189 if ((err = ltc_mp.ecc_mul2add(mG, u1, mQ, u2, mG, ma, m)) != CRYPT_OK) { goto error; }
190 }
191
192 /* v = X_x1 mod n */
193 if ((err = mp_mod(mG->x, p, v)) != CRYPT_OK) { goto error; }
194
195 /* does v == r */
196 if (mp_cmp(v, r) == LTC_MP_EQ) {
197 *stat = 1;
198 }
199
200 /* clear up and return */
201 err = CRYPT_OK;
202 error:
203 if (mG != NULL) ltc_ecc_del_point(mG);
204 if (mQ != NULL) ltc_ecc_del_point(mQ);
205 if (mu != NULL) mp_clear(mu);
206 if (ma != NULL) mp_clear(ma);
207 mp_clear_multi(r, s, v, w, u1, u2, e, a_plus3, NULL);
208 if (mp != NULL) mp_montgomery_free(mp);
209 return err;
210 }
211
212 #endif
213
214 /* ref: $Format:%D$ */
215 /* git commit: $Format:%H$ */
216 /* commit time: $Format:%ai$ */
217