1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis */
2 /* SPDX-License-Identifier: Unlicense */
3
4 #include "tomcrypt_private.h"
5
6 #ifdef LTC_MECC
7
8 /**
9 @file ecc_verify_hash.c
10 ECC Crypto, Tom St Denis
11 */
12
13 /**
14 Verify an ECC signature in RFC7518 format
15 @param sig The signature to verify
16 @param siglen The length of the signature (octets)
17 @param hash The hash (message digest) that was signed
18 @param hashlen The length of the hash (octets)
19 @param sigformat The format of the signature (ecc_signature_type)
20 @param stat Result of signature, 1==valid, 0==invalid
21 @param key The corresponding public ECC key
22 @return CRYPT_OK if successful (even if the signature is not valid)
23 */
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)24 int ecc_verify_hash_ex(const unsigned char *sig, unsigned long siglen,
25 const unsigned char *hash, unsigned long hashlen,
26 ecc_signature_type sigformat, int *stat, const ecc_key *key)
27 {
28 ecc_point *mG = NULL, *mQ = NULL;
29 void *r, *s, *v, *w, *u1, *u2, *e, *p, *m, *a, *a_plus3;
30 void *mu = NULL, *ma = NULL;
31 void *mp = NULL;
32 int err;
33 unsigned long pbits, pbytes, i, shift_right;
34 unsigned char ch, buf[MAXBLOCKSIZE];
35
36 LTC_ARGCHK(sig != NULL);
37 LTC_ARGCHK(hash != NULL);
38 LTC_ARGCHK(stat != NULL);
39 LTC_ARGCHK(key != NULL);
40
41 /* default to invalid signature */
42 *stat = 0;
43
44 /* allocate ints */
45 if ((err = mp_init_multi(&r, &s, &v, &w, &u1, &u2, &e, &a_plus3, LTC_NULL)) != CRYPT_OK) {
46 return err;
47 }
48
49 p = key->dp.order;
50 m = key->dp.prime;
51 a = key->dp.A;
52 if ((err = mp_add_d(a, 3, a_plus3)) != CRYPT_OK) {
53 goto error;
54 }
55
56 /* allocate points */
57 mG = ltc_ecc_new_point();
58 mQ = ltc_ecc_new_point();
59 if (mQ == NULL || mG == NULL) {
60 err = CRYPT_MEM;
61 goto error;
62 }
63
64 if (sigformat == LTC_ECCSIG_ANSIX962) {
65 /* ANSI X9.62 format - ASN.1 encoded SEQUENCE{ INTEGER(r), INTEGER(s) } */
66 if ((err = der_decode_sequence_multi_ex(sig, siglen, LTC_DER_SEQ_SEQUENCE | LTC_DER_SEQ_STRICT,
67 LTC_ASN1_INTEGER, 1UL, r,
68 LTC_ASN1_INTEGER, 1UL, s,
69 LTC_ASN1_EOL, 0UL, LTC_NULL)) != CRYPT_OK) { goto error; }
70 }
71 else if (sigformat == LTC_ECCSIG_RFC7518) {
72 /* RFC7518 format - raw (r,s) */
73 i = mp_unsigned_bin_size(key->dp.order);
74 if (siglen != (2 * i)) {
75 err = CRYPT_INVALID_PACKET;
76 goto error;
77 }
78 if ((err = mp_read_unsigned_bin(r, (unsigned char *)sig, i)) != CRYPT_OK) { goto error; }
79 if ((err = mp_read_unsigned_bin(s, (unsigned char *)sig+i, i)) != CRYPT_OK) { goto error; }
80 }
81 else if (sigformat == LTC_ECCSIG_ETH27) {
82 /* Ethereum (v,r,s) format */
83 if (pk_oid_cmp_with_ulong("1.3.132.0.10", key->dp.oid, key->dp.oidlen) != CRYPT_OK) {
84 /* Only valid for secp256k1 - OID 1.3.132.0.10 */
85 err = CRYPT_ERROR; goto error;
86 }
87 if (siglen != 65) { /* Only secp256k1 curves use this format, so must be 65 bytes long */
88 err = CRYPT_INVALID_PACKET;
89 goto error;
90 }
91 if ((err = mp_read_unsigned_bin(r, (unsigned char *)sig, 32)) != CRYPT_OK) { goto error; }
92 if ((err = mp_read_unsigned_bin(s, (unsigned char *)sig+32, 32)) != CRYPT_OK) { goto error; }
93 }
94 #ifdef LTC_SSH
95 else if (sigformat == LTC_ECCSIG_RFC5656) {
96 char name[64], name2[64];
97 unsigned long namelen = sizeof(name);
98 unsigned long name2len = sizeof(name2);
99
100 /* Decode as SSH data sequence, per RFC4251 */
101 if ((err = ssh_decode_sequence_multi(sig, &siglen,
102 LTC_SSHDATA_STRING, name, &namelen,
103 LTC_SSHDATA_MPINT, r,
104 LTC_SSHDATA_MPINT, s,
105 LTC_SSHDATA_EOL, NULL)) != CRYPT_OK) { goto error; }
106
107
108 /* Check curve matches identifier string */
109 if ((err = ecc_ssh_ecdsa_encode_name(name2, &name2len, key)) != CRYPT_OK) { goto error; }
110 if ((namelen != name2len) || (XSTRCMP(name, name2) != 0)) {
111 err = CRYPT_INVALID_ARG;
112 goto error;
113 }
114 }
115 #endif
116 else {
117 /* Unknown signature format */
118 err = CRYPT_ERROR;
119 goto error;
120 }
121
122 /* check for zero */
123 if (mp_cmp_d(r, 0) != LTC_MP_GT || mp_cmp_d(s, 0) != LTC_MP_GT ||
124 mp_cmp(r, p) != LTC_MP_LT || mp_cmp(s, p) != LTC_MP_LT) {
125 err = CRYPT_INVALID_PACKET;
126 goto error;
127 }
128
129 /* read hash - truncate if needed */
130 pbits = mp_count_bits(p);
131 pbytes = (pbits+7) >> 3;
132 if (pbits > hashlen*8) {
133 if ((err = mp_read_unsigned_bin(e, (unsigned char *)hash, hashlen)) != CRYPT_OK) { goto error; }
134 }
135 else if (pbits % 8 == 0) {
136 if ((err = mp_read_unsigned_bin(e, (unsigned char *)hash, pbytes)) != CRYPT_OK) { goto error; }
137 }
138 else {
139 shift_right = 8 - pbits % 8;
140 for (i=0, ch=0; i<pbytes; i++) {
141 buf[i] = ch;
142 ch = (hash[i] << (8-shift_right));
143 buf[i] = buf[i] ^ (hash[i] >> shift_right);
144 }
145 if ((err = mp_read_unsigned_bin(e, (unsigned char *)buf, pbytes)) != CRYPT_OK) { goto error; }
146 }
147
148 /* w = s^-1 mod n */
149 if ((err = mp_invmod(s, p, w)) != CRYPT_OK) { goto error; }
150
151 /* u1 = ew */
152 if ((err = mp_mulmod(e, w, p, u1)) != CRYPT_OK) { goto error; }
153
154 /* u2 = rw */
155 if ((err = mp_mulmod(r, w, p, u2)) != CRYPT_OK) { goto error; }
156
157 /* find mG and mQ */
158 if ((err = ltc_ecc_copy_point(&key->dp.base, mG)) != CRYPT_OK) { goto error; }
159 if ((err = ltc_ecc_copy_point(&key->pubkey, mQ)) != CRYPT_OK) { goto error; }
160
161 /* find the montgomery mp */
162 if ((err = mp_montgomery_setup(m, &mp)) != CRYPT_OK) { goto error; }
163
164 /* for curves with a == -3 keep ma == NULL */
165 if (mp_cmp(a_plus3, m) != LTC_MP_EQ) {
166 if ((err = mp_init_multi(&mu, &ma, LTC_NULL)) != CRYPT_OK) { goto error; }
167 if ((err = mp_montgomery_normalization(mu, m)) != CRYPT_OK) { goto error; }
168 if ((err = mp_mulmod(a, mu, m, ma)) != CRYPT_OK) { goto error; }
169 }
170
171 /* compute u1*mG + u2*mQ = mG */
172 if (ltc_mp.ecc_mul2add == NULL) {
173 if ((err = ltc_mp.ecc_ptmul(u1, mG, mG, a, m, 0)) != CRYPT_OK) { goto error; }
174 if ((err = ltc_mp.ecc_ptmul(u2, mQ, mQ, a, m, 0)) != CRYPT_OK) { goto error; }
175
176 /* add them */
177 if ((err = ltc_mp.ecc_ptadd(mQ, mG, mG, ma, m, mp)) != CRYPT_OK) { goto error; }
178
179 /* reduce */
180 if ((err = ltc_mp.ecc_map(mG, m, mp)) != CRYPT_OK) { goto error; }
181 } else {
182 /* use Shamir's trick to compute u1*mG + u2*mQ using half of the doubles */
183 if ((err = ltc_mp.ecc_mul2add(mG, u1, mQ, u2, mG, ma, m)) != CRYPT_OK) { goto error; }
184 }
185
186 /* v = X_x1 mod n */
187 if ((err = mp_mod(mG->x, p, v)) != CRYPT_OK) { goto error; }
188
189 /* does v == r */
190 if (mp_cmp(v, r) == LTC_MP_EQ) {
191 *stat = 1;
192 }
193
194 /* clear up and return */
195 err = CRYPT_OK;
196 error:
197 if (mG != NULL) ltc_ecc_del_point(mG);
198 if (mQ != NULL) ltc_ecc_del_point(mQ);
199 if (mu != NULL) mp_clear(mu);
200 if (ma != NULL) mp_clear(ma);
201 mp_clear_multi(r, s, v, w, u1, u2, e, a_plus3, LTC_NULL);
202 if (mp != NULL) mp_montgomery_free(mp);
203 return err;
204 }
205
206 #endif
207