Coverage Report

Created: 2022-07-22 12:05

/libfido2/src/ecdh.c
Line
Count
Source (jump to first uncovered line)
1
/*
2
 * Copyright (c) 2018-2021 Yubico AB. All rights reserved.
3
 * Use of this source code is governed by a BSD-style
4
 * license that can be found in the LICENSE file.
5
 */
6
7
#include <openssl/evp.h>
8
#include <openssl/sha.h>
9
#if defined(LIBRESSL_VERSION_NUMBER)
10
#include <openssl/hkdf.h>
11
#else
12
#include <openssl/kdf.h>
13
#endif
14
15
#include "fido.h"
16
#include "fido/es256.h"
17
18
#if defined(LIBRESSL_VERSION_NUMBER)
19
static int
20
hkdf_sha256(uint8_t *key, const char *info, const fido_blob_t *secret)
21
{
22
        const EVP_MD *md;
23
        uint8_t salt[32];
24
25
        memset(salt, 0, sizeof(salt));
26
        if ((md = EVP_sha256()) == NULL ||
27
            HKDF(key, SHA256_DIGEST_LENGTH, md, secret->ptr, secret->len, salt,
28
            sizeof(salt), (const uint8_t *)info, strlen(info)) != 1)
29
                return -1;
30
31
        return 0;
32
}
33
#else
34
static int
35
hkdf_sha256(uint8_t *key, char *info, fido_blob_t *secret)
36
878
{
37
878
        const EVP_MD *const_md;
38
878
        EVP_MD *md = NULL;
39
878
        EVP_PKEY_CTX *ctx = NULL;
40
878
        size_t keylen = SHA256_DIGEST_LENGTH;
41
878
        uint8_t salt[32];
42
878
        int ok = -1;
43
44
878
        memset(salt, 0, sizeof(salt));
45
878
        if (secret->len > INT_MAX || strlen(info) > INT_MAX) {
46
0
                fido_log_debug("%s: invalid param", __func__);
47
0
                goto fail;
48
0
        }
49
878
        if ((const_md = EVP_sha256()) == NULL ||
50
878
            (md = EVP_MD_meth_dup(const_md)) == NULL ||
51
878
            (ctx = EVP_PKEY_CTX_new_id(EVP_PKEY_HKDF, NULL)) == NULL) {
52
17
                fido_log_debug("%s: init", __func__);
53
17
                goto fail;
54
17
        }
55
861
        if (EVP_PKEY_derive_init(ctx) < 1 ||
56
861
            EVP_PKEY_CTX_set_hkdf_md(ctx, md) < 1 ||
57
861
            EVP_PKEY_CTX_set1_hkdf_salt(ctx, salt, sizeof(salt)) < 1 ||
58
861
            EVP_PKEY_CTX_set1_hkdf_key(ctx, secret->ptr, (int)secret->len) < 1 ||
59
861
            EVP_PKEY_CTX_add1_hkdf_info(ctx, (void *)info, (int)strlen(info)) < 1) {
60
43
                fido_log_debug("%s: EVP_PKEY_CTX", __func__);
61
43
                goto fail;
62
43
        }
63
818
        if (EVP_PKEY_derive(ctx, key, &keylen) < 1) {
64
10
                fido_log_debug("%s: EVP_PKEY_derive", __func__);
65
10
                goto fail;
66
10
        }
67
68
808
        ok = 0;
69
878
fail:
70
878
        if (md != NULL)
71
868
                EVP_MD_meth_free(md);
72
878
        if (ctx != NULL)
73
861
                EVP_PKEY_CTX_free(ctx);
74
75
878
        return ok;
76
808
}
77
#endif /* defined(LIBRESSL_VERSION_NUMBER) */
78
79
static int
80
kdf(uint8_t prot, fido_blob_t *key, /* const */ fido_blob_t *secret)
81
1.44k
{
82
1.44k
        char hmac_info[] = "CTAP2 HMAC key"; /* const */
83
1.44k
        char aes_info[] = "CTAP2 AES key"; /* const */
84
85
1.44k
        switch (prot) {
86
976
        case CTAP_PIN_PROTOCOL1:
87
                /* use sha256 on the resulting secret */
88
976
                key->len = SHA256_DIGEST_LENGTH;
89
976
                if ((key->ptr = calloc(1, key->len)) == NULL ||
90
976
                    SHA256(secret->ptr, secret->len, key->ptr) != key->ptr) {
91
12
                        fido_log_debug("%s: SHA256", __func__);
92
12
                        return -1;
93
12
                }
94
964
                break;
95
964
        case CTAP_PIN_PROTOCOL2:
96
                /* use two instances of hkdf-sha256 on the resulting secret */
97
465
                key->len = 2 * SHA256_DIGEST_LENGTH;
98
465
                if ((key->ptr = calloc(1, key->len)) == NULL ||
99
465
                    hkdf_sha256(key->ptr, hmac_info, secret) < 0 ||
100
465
                    hkdf_sha256(key->ptr + SHA256_DIGEST_LENGTH, aes_info,
101
419
                    secret) < 0) {
102
76
                        fido_log_debug("%s: hkdf", __func__);
103
76
                        return -1;
104
76
                }
105
389
                break;
106
389
        default:
107
0
                fido_log_debug("%s: unknown pin protocol %u", __func__, prot);
108
0
                return -1;
109
1.44k
        }
110
111
1.35k
        return 0;
112
1.44k
}
113
114
static int
115
do_ecdh(const fido_dev_t *dev, const es256_sk_t *sk, const es256_pk_t *pk,
116
    fido_blob_t **ecdh)
117
1.68k
{
118
1.68k
        EVP_PKEY *pk_evp = NULL;
119
1.68k
        EVP_PKEY *sk_evp = NULL;
120
1.68k
        EVP_PKEY_CTX *ctx = NULL;
121
1.68k
        fido_blob_t *secret = NULL;
122
1.68k
        int ok = -1;
123
124
1.68k
        *ecdh = NULL;
125
1.68k
        if ((secret = fido_blob_new()) == NULL ||
126
1.68k
            (*ecdh = fido_blob_new()) == NULL)
127
12
                goto fail;
128
1.67k
        if ((pk_evp = es256_pk_to_EVP_PKEY(pk)) == NULL ||
129
1.67k
            (sk_evp = es256_sk_to_EVP_PKEY(sk)) == NULL) {
130
185
                fido_log_debug("%s: es256_to_EVP_PKEY", __func__);
131
185
                goto fail;
132
185
        }
133
1.48k
        if ((ctx = EVP_PKEY_CTX_new(sk_evp, NULL)) == NULL ||
134
1.48k
            EVP_PKEY_derive_init(ctx) <= 0 ||
135
1.48k
            EVP_PKEY_derive_set_peer(ctx, pk_evp) <= 0) {
136
21
                fido_log_debug("%s: EVP_PKEY_derive_init", __func__);
137
21
                goto fail;
138
21
        }
139
1.46k
        if (EVP_PKEY_derive(ctx, NULL, &secret->len) <= 0 ||
140
1.46k
            (secret->ptr = calloc(1, secret->len)) == NULL ||
141
1.46k
            EVP_PKEY_derive(ctx, secret->ptr, &secret->len) <= 0) {
142
23
                fido_log_debug("%s: EVP_PKEY_derive", __func__);
143
23
                goto fail;
144
23
        }
145
1.44k
        if (kdf(fido_dev_get_pin_protocol(dev), *ecdh, secret) < 0) {
146
88
                fido_log_debug("%s: kdf", __func__);
147
88
                goto fail;
148
88
        }
149
150
1.35k
        ok = 0;
151
1.68k
fail:
152
1.68k
        if (pk_evp != NULL)
153
1.53k
                EVP_PKEY_free(pk_evp);
154
1.68k
        if (sk_evp != NULL)
155
1.48k
                EVP_PKEY_free(sk_evp);
156
1.68k
        if (ctx != NULL)
157
1.47k
                EVP_PKEY_CTX_free(ctx);
158
1.68k
        if (ok < 0)
159
329
                fido_blob_free(ecdh);
160
161
1.68k
        fido_blob_free(&secret);
162
163
1.68k
        return ok;
164
1.35k
}
165
166
int
167
fido_do_ecdh(fido_dev_t *dev, es256_pk_t **pk, fido_blob_t **ecdh, int *ms)
168
3.83k
{
169
3.83k
        es256_sk_t *sk = NULL; /* our private key */
170
3.83k
        es256_pk_t *ak = NULL; /* authenticator's public key */
171
3.83k
        int r;
172
173
3.83k
        *pk = NULL;
174
3.83k
        *ecdh = NULL;
175
3.83k
        if ((sk = es256_sk_new()) == NULL || (*pk = es256_pk_new()) == NULL) {
176
36
                r = FIDO_ERR_INTERNAL;
177
36
                goto fail;
178
36
        }
179
3.80k
        if (es256_sk_create(sk) < 0 || es256_derive_pk(sk, *pk) < 0) {
180
416
                fido_log_debug("%s: es256_derive_pk", __func__);
181
416
                r = FIDO_ERR_INTERNAL;
182
416
                goto fail;
183
416
        }
184
3.38k
        if ((ak = es256_pk_new()) == NULL ||
185
3.38k
            fido_dev_authkey(dev, ak, ms) != FIDO_OK) {
186
1.70k
                fido_log_debug("%s: fido_dev_authkey", __func__);
187
1.70k
                r = FIDO_ERR_INTERNAL;
188
1.70k
                goto fail;
189
1.70k
        }
190
1.68k
        if (do_ecdh(dev, sk, ak, ecdh) < 0) {
191
329
                fido_log_debug("%s: do_ecdh", __func__);
192
329
                r = FIDO_ERR_INTERNAL;
193
329
                goto fail;
194
329
        }
195
196
1.35k
        r = FIDO_OK;
197
3.83k
fail:
198
3.83k
        es256_sk_free(&sk);
199
3.83k
        es256_pk_free(&ak);
200
201
3.83k
        if (r != FIDO_OK) {
202
2.48k
                es256_pk_free(pk);
203
2.48k
                fido_blob_free(ecdh);
204
2.48k
        }
205
206
3.83k
        return r;
207
1.35k
}