/*

 * Copyright (c) 2018-2021 Yubico AB. All rights reserved.

 * Use of this source code is governed by a BSD-style

 * license that can be found in the LICENSE file.

 * SPDX-License-Identifier: BSD-2-Clause

 */

#include <openssl/evp.h>

#include <openssl/sha.h>

#if defined(LIBRESSL_VERSION_NUMBER)

#include <openssl/hkdf.h>

#else

#include <openssl/kdf.h>

#endif

#include "fido.h"

#include "fido/es256.h"

#if defined(LIBRESSL_VERSION_NUMBER)

static int

hkdf_sha256(uint8_t *key, const char *info, const fido_blob_t *secret)

{

        const EVP_MD *md;

        uint8_t salt[32];

        memset(salt, 0, sizeof(salt));

        if ((md = EVP_sha256()) == NULL ||

            HKDF(key, SHA256_DIGEST_LENGTH, md, secret->ptr, secret->len, salt,

            sizeof(salt), (const uint8_t *)info, strlen(info)) != 1)

                return -1;

        return 0;

}

#else

static int

hkdf_sha256(uint8_t *key, char *info, fido_blob_t *secret)

{

        const EVP_MD *const_md;

        EVP_MD *md = NULL;

        EVP_PKEY_CTX *ctx = NULL;

        size_t keylen = SHA256_DIGEST_LENGTH;

        uint8_t salt[32];

        int ok = -1;

        memset(salt, 0, sizeof(salt));

        if (secret->len > INT_MAX || strlen(info) > INT_MAX) {

                fido_log_debug("%s: invalid param", __func__);

                goto fail;

        }

        if ((const_md = EVP_sha256()) == NULL ||

            (md = EVP_MD_meth_dup(const_md)) == NULL ||

            (ctx = EVP_PKEY_CTX_new_id(EVP_PKEY_HKDF, NULL)) == NULL) {

                fido_log_debug("%s: init", __func__);

                goto fail;

        }

        if (EVP_PKEY_derive_init(ctx) < 1 ||

            EVP_PKEY_CTX_set_hkdf_md(ctx, md) < 1 ||

            EVP_PKEY_CTX_set1_hkdf_salt(ctx, salt, sizeof(salt)) < 1 ||

            EVP_PKEY_CTX_set1_hkdf_key(ctx, secret->ptr, (int)secret->len) < 1 ||

            EVP_PKEY_CTX_add1_hkdf_info(ctx, (void *)info, (int)strlen(info)) < 1) {

                fido_log_debug("%s: EVP_PKEY_CTX", __func__);

                goto fail;

        }

        if (EVP_PKEY_derive(ctx, key, &keylen) < 1) {

                fido_log_debug("%s: EVP_PKEY_derive", __func__);

                goto fail;

        }

        ok = 0;

fail:

        if (md != NULL)

                EVP_MD_meth_free(md);

        if (ctx != NULL)

                EVP_PKEY_CTX_free(ctx);

        return ok;

}

#endif /* defined(LIBRESSL_VERSION_NUMBER) */

static int

kdf(uint8_t prot, fido_blob_t *key, /* const */ fido_blob_t *secret)

{

        char hmac_info[] = "CTAP2 HMAC key"; /* const */

        char aes_info[] = "CTAP2 AES key"; /* const */

        switch (prot) {

        case CTAP_PIN_PROTOCOL1:

                /* use sha256 on the resulting secret */

                key->len = SHA256_DIGEST_LENGTH;

                if ((key->ptr = calloc(1, key->len)) == NULL ||

                    SHA256(secret->ptr, secret->len, key->ptr) != key->ptr) {

                        fido_log_debug("%s: SHA256", __func__);

                        return -1;

                }

                break;

        case CTAP_PIN_PROTOCOL2:

                /* use two instances of hkdf-sha256 on the resulting secret */

                key->len = 2 * SHA256_DIGEST_LENGTH;

                if ((key->ptr = calloc(1, key->len)) == NULL ||

                    hkdf_sha256(key->ptr, hmac_info, secret) < 0 ||

                    hkdf_sha256(key->ptr + SHA256_DIGEST_LENGTH, aes_info,

                    secret) < 0) {

                        fido_log_debug("%s: hkdf", __func__);

                        return -1;

                }

                break;

        default:

                fido_log_debug("%s: unknown pin protocol %u", __func__, prot);

                return -1;

        }

        return 0;

}

static int

do_ecdh(const fido_dev_t *dev, const es256_sk_t *sk, const es256_pk_t *pk,

    fido_blob_t **ecdh)

{

        EVP_PKEY *pk_evp = NULL;

        EVP_PKEY *sk_evp = NULL;

        EVP_PKEY_CTX *ctx = NULL;

        fido_blob_t *secret = NULL;

        int ok = -1;

        *ecdh = NULL;

        if ((secret = fido_blob_new()) == NULL ||

            (*ecdh = fido_blob_new()) == NULL)

                goto fail;

        if ((pk_evp = es256_pk_to_EVP_PKEY(pk)) == NULL ||

            (sk_evp = es256_sk_to_EVP_PKEY(sk)) == NULL) {

                fido_log_debug("%s: es256_to_EVP_PKEY", __func__);

                goto fail;

        }

        if ((ctx = EVP_PKEY_CTX_new(sk_evp, NULL)) == NULL ||

            EVP_PKEY_derive_init(ctx) <= 0 ||

            EVP_PKEY_derive_set_peer(ctx, pk_evp) <= 0) {

                fido_log_debug("%s: EVP_PKEY_derive_init", __func__);

                goto fail;

        }

        if (EVP_PKEY_derive(ctx, NULL, &secret->len) <= 0 ||

            (secret->ptr = calloc(1, secret->len)) == NULL ||

            EVP_PKEY_derive(ctx, secret->ptr, &secret->len) <= 0) {

                fido_log_debug("%s: EVP_PKEY_derive", __func__);

                goto fail;

        }

        if (kdf(fido_dev_get_pin_protocol(dev), *ecdh, secret) < 0) {

                fido_log_debug("%s: kdf", __func__);

                goto fail;

        }

        ok = 0;

fail:

        if (pk_evp != NULL)

                EVP_PKEY_free(pk_evp);

        if (sk_evp != NULL)

                EVP_PKEY_free(sk_evp);

        if (ctx != NULL)

                EVP_PKEY_CTX_free(ctx);

        if (ok < 0)

                fido_blob_free(ecdh);

        fido_blob_free(&secret);

        return ok;

}

int

fido_do_ecdh(fido_dev_t *dev, es256_pk_t **pk, fido_blob_t **ecdh, int *ms)

{

        es256_sk_t *sk = NULL; /* our private key */

        es256_pk_t *ak = NULL; /* authenticator's public key */

        int r;

        *pk = NULL;

        *ecdh = NULL;

        if ((sk = es256_sk_new()) == NULL || (*pk = es256_pk_new()) == NULL) {

                r = FIDO_ERR_INTERNAL;

                goto fail;

        }

        if (es256_sk_create(sk) < 0 || es256_derive_pk(sk, *pk) < 0) {

                fido_log_debug("%s: es256_derive_pk", __func__);

                r = FIDO_ERR_INTERNAL;

                goto fail;

        }

        if ((ak = es256_pk_new()) == NULL ||

            fido_dev_authkey(dev, ak, ms) != FIDO_OK) {

                fido_log_debug("%s: fido_dev_authkey", __func__);

                r = FIDO_ERR_INTERNAL;

                goto fail;

        }

        if (do_ecdh(dev, sk, ak, ecdh) < 0) {

                fido_log_debug("%s: do_ecdh", __func__);

                r = FIDO_ERR_INTERNAL;

                goto fail;

        }

        r = FIDO_OK;

fail:

        es256_sk_free(&sk);

        es256_pk_free(&ak);

        if (r != FIDO_OK) {

                es256_pk_free(pk);

                fido_blob_free(ecdh);

        }

        return r;

}