Coverage Report

Created: 2024-06-03 09:43

/libfido2/src/ecdh.c
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Count
Source (jump to first uncovered line)
1
/*
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 * Copyright (c) 2018-2021 Yubico AB. All rights reserved.
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 * Use of this source code is governed by a BSD-style
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 * license that can be found in the LICENSE file.
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 * SPDX-License-Identifier: BSD-2-Clause
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 */
7
8
#include <openssl/evp.h>
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#include <openssl/sha.h>
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#if defined(LIBRESSL_VERSION_NUMBER)
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#include <openssl/hkdf.h>
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#else
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#include <openssl/kdf.h>
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#endif
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16
#include "fido.h"
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#include "fido/es256.h"
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19
#if defined(LIBRESSL_VERSION_NUMBER)
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static int
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hkdf_sha256(uint8_t *key, const char *info, const fido_blob_t *secret)
22
{
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        const EVP_MD *md;
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        uint8_t salt[32];
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26
        memset(salt, 0, sizeof(salt));
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        if ((md = EVP_sha256()) == NULL ||
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            HKDF(key, SHA256_DIGEST_LENGTH, md, secret->ptr, secret->len, salt,
29
            sizeof(salt), (const uint8_t *)info, strlen(info)) != 1)
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                return -1;
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32
        return 0;
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}
34
#else
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static int
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hkdf_sha256(uint8_t *key, char *info, fido_blob_t *secret)
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1.60k
{
38
1.60k
        const EVP_MD *const_md;
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1.60k
        EVP_MD *md = NULL;
40
1.60k
        EVP_PKEY_CTX *ctx = NULL;
41
1.60k
        size_t keylen = SHA256_DIGEST_LENGTH;
42
1.60k
        uint8_t salt[32];
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1.60k
        int ok = -1;
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45
1.60k
        memset(salt, 0, sizeof(salt));
46
1.60k
        if (secret->len > INT_MAX || strlen(info) > INT_MAX) {
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0
                fido_log_debug("%s: invalid param", __func__);
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0
                goto fail;
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0
        }
50
1.60k
        if ((const_md = EVP_sha256()) == NULL ||
51
1.60k
            (md = EVP_MD_meth_dup(const_md)) == NULL ||
52
1.60k
            (ctx = EVP_PKEY_CTX_new_id(EVP_PKEY_HKDF, NULL)) == NULL) {
53
42
                fido_log_debug("%s: init", __func__);
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42
                goto fail;
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42
        }
56
1.56k
        if (EVP_PKEY_derive_init(ctx) < 1 ||
57
1.56k
            EVP_PKEY_CTX_set_hkdf_md(ctx, md) < 1 ||
58
1.56k
            EVP_PKEY_CTX_set1_hkdf_salt(ctx, salt, sizeof(salt)) < 1 ||
59
1.56k
            EVP_PKEY_CTX_set1_hkdf_key(ctx, secret->ptr, (int)secret->len) < 1 ||
60
1.56k
            EVP_PKEY_CTX_add1_hkdf_info(ctx, (void *)info, (int)strlen(info)) < 1) {
61
35
                fido_log_debug("%s: EVP_PKEY_CTX", __func__);
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35
                goto fail;
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35
        }
64
1.52k
        if (EVP_PKEY_derive(ctx, key, &keylen) < 1) {
65
36
                fido_log_debug("%s: EVP_PKEY_derive", __func__);
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36
                goto fail;
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36
        }
68
69
1.49k
        ok = 0;
70
1.60k
fail:
71
1.60k
        if (md != NULL)
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1.58k
                EVP_MD_meth_free(md);
73
1.60k
        if (ctx != NULL)
74
1.56k
                EVP_PKEY_CTX_free(ctx);
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76
1.60k
        return ok;
77
1.49k
}
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#endif /* defined(LIBRESSL_VERSION_NUMBER) */
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80
static int
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kdf(uint8_t prot, fido_blob_t *key, /* const */ fido_blob_t *secret)
82
5.00k
{
83
5.00k
        char hmac_info[] = "CTAP2 HMAC key"; /* const */
84
5.00k
        char aes_info[] = "CTAP2 AES key"; /* const */
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86
5.00k
        switch (prot) {
87
4.15k
        case CTAP_PIN_PROTOCOL1:
88
                /* use sha256 on the resulting secret */
89
4.15k
                key->len = SHA256_DIGEST_LENGTH;
90
4.15k
                if ((key->ptr = calloc(1, key->len)) == NULL ||
91
4.15k
                    SHA256(secret->ptr, secret->len, key->ptr) != key->ptr) {
92
32
                        fido_log_debug("%s: SHA256", __func__);
93
32
                        return -1;
94
32
                }
95
4.12k
                break;
96
4.12k
        case CTAP_PIN_PROTOCOL2:
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                /* use two instances of hkdf-sha256 on the resulting secret */
98
848
                key->len = 2 * SHA256_DIGEST_LENGTH;
99
848
                if ((key->ptr = calloc(1, key->len)) == NULL ||
100
848
                    hkdf_sha256(key->ptr, hmac_info, secret) < 0 ||
101
848
                    hkdf_sha256(key->ptr + SHA256_DIGEST_LENGTH, aes_info,
102
772
                    secret) < 0) {
103
127
                        fido_log_debug("%s: hkdf", __func__);
104
127
                        return -1;
105
127
                }
106
721
                break;
107
721
        default:
108
0
                fido_log_debug("%s: unknown pin protocol %u", __func__, prot);
109
0
                return -1;
110
5.00k
        }
111
112
4.84k
        return 0;
113
5.00k
}
114
115
static int
116
do_ecdh(const fido_dev_t *dev, const es256_sk_t *sk, const es256_pk_t *pk,
117
    fido_blob_t **ecdh)
118
6.74k
{
119
6.74k
        EVP_PKEY *pk_evp = NULL;
120
6.74k
        EVP_PKEY *sk_evp = NULL;
121
6.74k
        EVP_PKEY_CTX *ctx = NULL;
122
6.74k
        fido_blob_t *secret = NULL;
123
6.74k
        int ok = -1;
124
125
6.74k
        *ecdh = NULL;
126
6.74k
        if ((secret = fido_blob_new()) == NULL ||
127
6.74k
            (*ecdh = fido_blob_new()) == NULL)
128
34
                goto fail;
129
6.70k
        if ((pk_evp = es256_pk_to_EVP_PKEY(pk)) == NULL ||
130
6.70k
            (sk_evp = es256_sk_to_EVP_PKEY(sk)) == NULL) {
131
1.51k
                fido_log_debug("%s: es256_to_EVP_PKEY", __func__);
132
1.51k
                goto fail;
133
1.51k
        }
134
5.18k
        if ((ctx = EVP_PKEY_CTX_new(sk_evp, NULL)) == NULL ||
135
5.18k
            EVP_PKEY_derive_init(ctx) <= 0 ||
136
5.18k
            EVP_PKEY_derive_set_peer(ctx, pk_evp) <= 0) {
137
97
                fido_log_debug("%s: EVP_PKEY_derive_init", __func__);
138
97
                goto fail;
139
97
        }
140
5.09k
        if (EVP_PKEY_derive(ctx, NULL, &secret->len) <= 0 ||
141
5.09k
            (secret->ptr = calloc(1, secret->len)) == NULL ||
142
5.09k
            EVP_PKEY_derive(ctx, secret->ptr, &secret->len) <= 0) {
143
88
                fido_log_debug("%s: EVP_PKEY_derive", __func__);
144
88
                goto fail;
145
88
        }
146
5.00k
        if (kdf(fido_dev_get_pin_protocol(dev), *ecdh, secret) < 0) {
147
159
                fido_log_debug("%s: kdf", __func__);
148
159
                goto fail;
149
159
        }
150
151
4.84k
        ok = 0;
152
6.74k
fail:
153
6.74k
        if (pk_evp != NULL)
154
5.32k
                EVP_PKEY_free(pk_evp);
155
6.74k
        if (sk_evp != NULL)
156
5.18k
                EVP_PKEY_free(sk_evp);
157
6.74k
        if (ctx != NULL)
158
5.16k
                EVP_PKEY_CTX_free(ctx);
159
6.74k
        if (ok < 0)
160
1.89k
                fido_blob_free(ecdh);
161
162
6.74k
        fido_blob_free(&secret);
163
164
6.74k
        return ok;
165
4.84k
}
166
167
int
168
fido_do_ecdh(fido_dev_t *dev, es256_pk_t **pk, fido_blob_t **ecdh, int *ms)
169
15.5k
{
170
15.5k
        es256_sk_t *sk = NULL; /* our private key */
171
15.5k
        es256_pk_t *ak = NULL; /* authenticator's public key */
172
15.5k
        int r;
173
174
15.5k
        *pk = NULL;
175
15.5k
        *ecdh = NULL;
176
15.5k
        if ((sk = es256_sk_new()) == NULL || (*pk = es256_pk_new()) == NULL) {
177
86
                r = FIDO_ERR_INTERNAL;
178
86
                goto fail;
179
86
        }
180
15.4k
        if (es256_sk_create(sk) < 0 || es256_derive_pk(sk, *pk) < 0) {
181
1.70k
                fido_log_debug("%s: es256_derive_pk", __func__);
182
1.70k
                r = FIDO_ERR_INTERNAL;
183
1.70k
                goto fail;
184
1.70k
        }
185
13.7k
        if ((ak = es256_pk_new()) == NULL ||
186
13.7k
            fido_dev_authkey(dev, ak, ms) != FIDO_OK) {
187
7.04k
                fido_log_debug("%s: fido_dev_authkey", __func__);
188
7.04k
                r = FIDO_ERR_INTERNAL;
189
7.04k
                goto fail;
190
7.04k
        }
191
6.74k
        if (do_ecdh(dev, sk, ak, ecdh) < 0) {
192
1.89k
                fido_log_debug("%s: do_ecdh", __func__);
193
1.89k
                r = FIDO_ERR_INTERNAL;
194
1.89k
                goto fail;
195
1.89k
        }
196
197
4.84k
        r = FIDO_OK;
198
15.5k
fail:
199
15.5k
        es256_sk_free(&sk);
200
15.5k
        es256_pk_free(&ak);
201
202
15.5k
        if (r != FIDO_OK) {
203
10.7k
                es256_pk_free(pk);
204
10.7k
                fido_blob_free(ecdh);
205
10.7k
        }
206
207
15.5k
        return r;
208
4.84k
}