Coverage Report

Created: 2021-03-26 11:35

/libfido2/src/ecdh.c
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Source (jump to first uncovered line)
1
/*
2
 * 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.
5
 */
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7
#include <openssl/evp.h>
8
#include <openssl/sha.h>
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#if defined(LIBRESSL_VERSION_NUMBER)
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#include <openssl/hkdf.h>
11
#else
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#include <openssl/kdf.h>
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#endif
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15
#include "fido.h"
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#include "fido/es256.h"
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18
#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)
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{
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        const EVP_MD *md;
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        uint8_t salt[32];
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25
        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,
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            sizeof(salt), (const uint8_t *)info, strlen(info)) != 1)
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                return -1;
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31
        return 0;
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}
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#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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731
{
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731
        const EVP_MD *const_md;
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731
        EVP_MD *md = NULL;
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731
        EVP_PKEY_CTX *ctx = NULL;
40
731
        size_t keylen = SHA256_DIGEST_LENGTH;
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731
        uint8_t salt[32];
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731
        int ok = -1;
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731
44
731
        memset(salt, 0, sizeof(salt));
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731
        if (secret->len > INT_MAX || strlen(info) > INT_MAX) {
46
0
                fido_log_debug("%s: invalid param", __func__);
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0
                goto fail;
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0
        }
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731
        if ((const_md = EVP_sha256()) == NULL ||
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731
            (md = EVP_MD_meth_dup(const_md)) == NULL ||
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731
            (ctx = EVP_PKEY_CTX_new_id(EVP_PKEY_HKDF, NULL)) == NULL) {
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17
                fido_log_debug("%s: init", __func__);
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17
                goto fail;
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17
        }
55
714
        if (EVP_PKEY_derive_init(ctx) < 1 ||
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714
            EVP_PKEY_CTX_set_hkdf_md(ctx, md) < 1 ||
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714
            EVP_PKEY_CTX_set1_hkdf_salt(ctx, salt, sizeof(salt)) < 1 ||
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714
            EVP_PKEY_CTX_set1_hkdf_key(ctx, secret->ptr, (int)secret->len) < 1 ||
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714
            EVP_PKEY_CTX_add1_hkdf_info(ctx, info, (int)strlen(info)) < 1) {
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15
                fido_log_debug("%s: EVP_PKEY_CTX", __func__);
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15
                goto fail;
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15
        }
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699
        if (EVP_PKEY_derive(ctx, key, &keylen) < 1) {
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15
                fido_log_debug("%s: EVP_PKEY_derive", __func__);
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15
                goto fail;
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15
        }
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684
68
684
        ok = 0;
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731
fail:
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731
        if (md != NULL)
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731
                EVP_MD_meth_free(md);
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731
        if (ctx != NULL)
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731
                EVP_PKEY_CTX_free(ctx);
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731
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731
        return ok;
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684
}
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#endif
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79
static int
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kdf(uint8_t prot, fido_blob_t *key, /* const */ fido_blob_t *secret)
81
3.30k
{
82
3.30k
        char hmac_info[] = "CTAP2 HMAC key"; /* const */
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3.30k
        char aes_info[] = "CTAP2 AES key"; /* const */
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3.30k
85
3.30k
        switch (prot) {
86
2.92k
        case CTAP_PIN_PROTOCOL1:
87
2.92k
                /* use sha256 on the resulting secret */
88
2.92k
                key->len = SHA256_DIGEST_LENGTH;
89
2.92k
                if ((key->ptr = calloc(1, key->len)) == NULL ||
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2.92k
                    SHA256(secret->ptr, secret->len, key->ptr) != key->ptr) {
91
21
                        fido_log_debug("%s: SHA256", __func__);
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21
                        return -1;
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21
                }
94
2.90k
                break;
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2.90k
        case CTAP_PIN_PROTOCOL2:
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386
                /* use two instances of hkdf-sha256 on the resulting secret */
97
386
                key->len = 2 * SHA256_DIGEST_LENGTH;
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386
                if ((key->ptr = calloc(1, key->len)) == NULL ||
99
386
                    hkdf_sha256(key->ptr, hmac_info, secret) < 0 ||
100
386
                    hkdf_sha256(key->ptr + SHA256_DIGEST_LENGTH, aes_info,
101
352
                    secret) < 0) {
102
54
                        fido_log_debug("%s: hkdf", __func__);
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54
                        return -1;
104
54
                }
105
332
                break;
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332
        default:
107
0
                fido_log_debug("%s: unknown pin protocol %u", __func__, prot);
108
0
                return -1;
109
3.23k
        }
110
3.23k
111
3.23k
        return 0;
112
3.23k
}
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
3.73k
{
118
3.73k
        EVP_PKEY *pk_evp = NULL;
119
3.73k
        EVP_PKEY *sk_evp = NULL;
120
3.73k
        EVP_PKEY_CTX *ctx = NULL;
121
3.73k
        fido_blob_t *secret = NULL;
122
3.73k
        int ok = -1;
123
3.73k
124
3.73k
        *ecdh = NULL;
125
3.73k
        if ((secret = fido_blob_new()) == NULL ||
126
3.73k
            (*ecdh = fido_blob_new()) == NULL)
127
3.73k
                goto fail;
128
3.71k
        if ((pk_evp = es256_pk_to_EVP_PKEY(pk)) == NULL ||
129
3.71k
            (sk_evp = es256_sk_to_EVP_PKEY(sk)) == NULL) {
130
331
                fido_log_debug("%s: es256_to_EVP_PKEY", __func__);
131
331
                goto fail;
132
331
        }
133
3.38k
        if ((ctx = EVP_PKEY_CTX_new(sk_evp, NULL)) == NULL ||
134
3.38k
            EVP_PKEY_derive_init(ctx) <= 0 ||
135
3.38k
            EVP_PKEY_derive_set_peer(ctx, pk_evp) <= 0) {
136
40
                fido_log_debug("%s: EVP_PKEY_derive_init", __func__);
137
40
                goto fail;
138
40
        }
139
3.34k
        if (EVP_PKEY_derive(ctx, NULL, &secret->len) <= 0 ||
140
3.34k
            (secret->ptr = calloc(1, secret->len)) == NULL ||
141
3.34k
            EVP_PKEY_derive(ctx, secret->ptr, &secret->len) <= 0) {
142
33
                fido_log_debug("%s: EVP_PKEY_derive", __func__);
143
33
                goto fail;
144
33
        }
145
3.30k
        if (kdf(fido_dev_get_pin_protocol(dev), *ecdh, secret) < 0) {
146
75
                fido_log_debug("%s: kdf", __func__);
147
75
                goto fail;
148
75
        }
149
3.23k
150
3.23k
        ok = 0;
151
3.73k
fail:
152
3.73k
        if (pk_evp != NULL)
153
3.73k
                EVP_PKEY_free(pk_evp);
154
3.73k
        if (sk_evp != NULL)
155
3.73k
                EVP_PKEY_free(sk_evp);
156
3.73k
        if (ctx != NULL)
157
3.73k
                EVP_PKEY_CTX_free(ctx);
158
3.73k
        if (ok < 0)
159
498
                fido_blob_free(ecdh);
160
3.73k
161
3.73k
        fido_blob_free(&secret);
162
3.73k
163
3.73k
        return ok;
164
3.23k
}
165
166
int
167
fido_do_ecdh(fido_dev_t *dev, es256_pk_t **pk, fido_blob_t **ecdh)
168
6.31k
{
169
6.31k
        es256_sk_t *sk = NULL; /* our private key */
170
6.31k
        es256_pk_t *ak = NULL; /* authenticator's public key */
171
6.31k
        int r;
172
6.31k
173
6.31k
        *pk = NULL;
174
6.31k
        *ecdh = NULL;
175
6.31k
        if ((sk = es256_sk_new()) == NULL || (*pk = es256_pk_new()) == NULL) {
176
54
                r = FIDO_ERR_INTERNAL;
177
54
                goto fail;
178
54
        }
179
6.26k
        if (es256_sk_create(sk) < 0 || es256_derive_pk(sk, *pk) < 0) {
180
577
                fido_log_debug("%s: es256_derive_pk", __func__);
181
577
                r = FIDO_ERR_INTERNAL;
182
577
                goto fail;
183
577
        }
184
5.68k
        if ((ak = es256_pk_new()) == NULL ||
185
5.68k
            fido_dev_authkey(dev, ak) != FIDO_OK) {
186
1.95k
                fido_log_debug("%s: fido_dev_authkey", __func__);
187
1.95k
                r = FIDO_ERR_INTERNAL;
188
1.95k
                goto fail;
189
1.95k
        }
190
3.73k
        if (do_ecdh(dev, sk, ak, ecdh) < 0) {
191
498
                fido_log_debug("%s: do_ecdh", __func__);
192
498
                r = FIDO_ERR_INTERNAL;
193
498
                goto fail;
194
498
        }
195
3.23k
196
3.23k
        r = FIDO_OK;
197
6.31k
fail:
198
6.31k
        es256_sk_free(&sk);
199
6.31k
        es256_pk_free(&ak);
200
6.31k
201
6.31k
        if (r != FIDO_OK) {
202
3.08k
                es256_pk_free(pk);
203
3.08k
                fido_blob_free(ecdh);
204
3.08k
        }
205
6.31k
206
6.31k
        return r;
207
3.23k
}