1 /*
2 * SPDX-FileCopyrightText: 2014, Kenneth MacKay
3 *
4 * SPDX-License-Identifier: BSD-2-Clause
5 *
6 * SPDX-FileContributor: 2020-2021 Espressif Systems (Shanghai) CO LTD
7 */
8
9 /* uECC_verify() calls a number of static functions form here and
10 uses other definitions, so we just build that whole source file here and then append
11 our modified version uECC_verify_antifault(). */
12 #include "micro-ecc/uECC.c"
13
14 /* Version of uECC_verify() which also copies message_hash into verified_hash,
15 but only if the signature is valid. Does this in an FI resistant way.
16 */
uECC_verify_antifault(const uint8_t * public_key,const uint8_t * message_hash,unsigned hash_size,const uint8_t * signature,uECC_Curve curve,uint8_t * verified_hash)17 int uECC_verify_antifault(const uint8_t *public_key,
18 const uint8_t *message_hash,
19 unsigned hash_size,
20 const uint8_t *signature,
21 uECC_Curve curve,
22 uint8_t *verified_hash) {
23 uECC_word_t u1[uECC_MAX_WORDS], u2[uECC_MAX_WORDS];
24 uECC_word_t z[uECC_MAX_WORDS];
25 uECC_word_t sum[uECC_MAX_WORDS * 2];
26 uECC_word_t rx[uECC_MAX_WORDS];
27 uECC_word_t ry[uECC_MAX_WORDS];
28 uECC_word_t tx[uECC_MAX_WORDS];
29 uECC_word_t ty[uECC_MAX_WORDS];
30 uECC_word_t tz[uECC_MAX_WORDS];
31 const uECC_word_t *points[4];
32 const uECC_word_t *point;
33 bitcount_t num_bits;
34 bitcount_t i;
35 #if uECC_VLI_NATIVE_LITTLE_ENDIAN
36 uECC_word_t *_public = (uECC_word_t *)public_key;
37 #else
38 uECC_word_t _public[uECC_MAX_WORDS * 2];
39 #endif
40 uECC_word_t r[uECC_MAX_WORDS], s[uECC_MAX_WORDS];
41 wordcount_t num_words = curve->num_words;
42 wordcount_t num_n_words = BITS_TO_WORDS(curve->num_n_bits);
43
44 rx[num_n_words - 1] = 0;
45 r[num_n_words - 1] = 0;
46 s[num_n_words - 1] = 0;
47
48 #if uECC_VLI_NATIVE_LITTLE_ENDIAN
49 bcopy((uint8_t *) r, signature, curve->num_bytes);
50 bcopy((uint8_t *) s, signature + curve->num_bytes, curve->num_bytes);
51 #else
52 uECC_vli_bytesToNative(_public, public_key, curve->num_bytes);
53 uECC_vli_bytesToNative(
54 _public + num_words, public_key + curve->num_bytes, curve->num_bytes);
55 uECC_vli_bytesToNative(r, signature, curve->num_bytes);
56 uECC_vli_bytesToNative(s, signature + curve->num_bytes, curve->num_bytes);
57 #endif
58
59 /* r, s must not be 0. */
60 if (uECC_vli_isZero(r, num_words) || uECC_vli_isZero(s, num_words)) {
61 return 0;
62 }
63
64 /* r, s must be < n. */
65 if (uECC_vli_cmp(curve->n, r, num_n_words) != 1 ||
66 uECC_vli_cmp(curve->n, s, num_n_words) != 1) {
67 return 0;
68 }
69
70 /* Calculate u1 and u2. */
71 uECC_vli_modInv(z, s, curve->n, num_n_words); /* z = 1/s */
72 u1[num_n_words - 1] = 0;
73 bits2int(u1, message_hash, hash_size, curve);
74 uECC_vli_modMult(u1, u1, z, curve->n, num_n_words); /* u1 = e/s */
75 uECC_vli_modMult(u2, r, z, curve->n, num_n_words); /* u2 = r/s */
76
77 /* Calculate sum = G + Q. */
78 uECC_vli_set(sum, _public, num_words);
79 uECC_vli_set(sum + num_words, _public + num_words, num_words);
80 uECC_vli_set(tx, curve->G, num_words);
81 uECC_vli_set(ty, curve->G + num_words, num_words);
82 uECC_vli_modSub(z, sum, tx, curve->p, num_words); /* z = x2 - x1 */
83 XYcZ_add(tx, ty, sum, sum + num_words, curve);
84 uECC_vli_modInv(z, z, curve->p, num_words); /* z = 1/z */
85 apply_z(sum, sum + num_words, z, curve);
86
87 /* Use Shamir's trick to calculate u1*G + u2*Q */
88 points[0] = 0;
89 points[1] = curve->G;
90 points[2] = _public;
91 points[3] = sum;
92 num_bits = smax(uECC_vli_numBits(u1, num_n_words),
93 uECC_vli_numBits(u2, num_n_words));
94
95 point = points[(!!uECC_vli_testBit(u1, num_bits - 1)) |
96 ((!!uECC_vli_testBit(u2, num_bits - 1)) << 1)];
97 uECC_vli_set(rx, point, num_words);
98 uECC_vli_set(ry, point + num_words, num_words);
99 uECC_vli_clear(z, num_words);
100 z[0] = 1;
101
102 for (i = num_bits - 2; i >= 0; --i) {
103 uECC_word_t index;
104 curve->double_jacobian(rx, ry, z, curve);
105
106 index = (!!uECC_vli_testBit(u1, i)) | ((!!uECC_vli_testBit(u2, i)) << 1);
107 point = points[index];
108 if (point) {
109 uECC_vli_set(tx, point, num_words);
110 uECC_vli_set(ty, point + num_words, num_words);
111 apply_z(tx, ty, z, curve);
112 uECC_vli_modSub(tz, rx, tx, curve->p, num_words); /* Z = x2 - x1 */
113 XYcZ_add(tx, ty, rx, ry, curve);
114 uECC_vli_modMult_fast(z, z, tz, curve);
115 }
116 }
117
118 uECC_vli_modInv(z, z, curve->p, num_words); /* Z = 1/Z */
119 apply_z(rx, ry, z, curve);
120
121 /* v = x1 (mod n) */
122 if (uECC_vli_cmp(curve->n, rx, num_n_words) != 1) {
123 uECC_vli_sub(rx, rx, curve->n, num_n_words);
124 }
125
126 /* Anti-FI addition. Copy message_hash into verified_hash, but do it in a
127 way that it will only happen if v == r (ie, rx == r)
128 */
129 const uECC_word_t *mhash_words = (const uECC_word_t *)message_hash;
130 uECC_word_t *vhash_words = (uECC_word_t *)verified_hash;
131 unsigned hash_words = hash_size / sizeof(uECC_word_t);
132 for (unsigned int w = 0; w < hash_words; w++) {
133 /* note: using curve->num_words here to encourage compiler to re-read this variable */
134 vhash_words[w] = mhash_words[w] ^ rx[w % curve->num_words] ^ r[w % curve->num_words];
135 }
136 /* Curve may be longer than hash, in which case keep reading the rest of the bytes */
137 for (int w = hash_words; w < curve->num_words; w++) {
138 vhash_words[w % hash_words] |= rx[w] ^ r[w];
139 }
140
141 /* Accept only if v == r. */
142 return (int)(uECC_vli_equal(rx, r, num_words));
143 }
144
