/*
 * CDDL HEADER START
 *
 * This file and its contents are supplied under the terms of the
 * Common Development and Distribution License ("CDDL"), version 1.0.
 * You may only use this file in accordance with the terms of version
 * 1.0 of the CDDL.
 *
 * A full copy of the text of the CDDL should have accompanied this
 * source.  A copy of the CDDL is also available via the Internet at
 * http://www.illumos.org/license/CDDL.
 *
 * CDDL HEADER END
 */

/*
 * Copyright (c) 2017, Datto, Inc. All rights reserved.
 */

#include <sys/dmu.h>
#include <sys/hkdf.h>
#include <sys/freebsd_crypto.h>
#include <sys/hkdf.h>

static int
hkdf_sha512_extract(uint8_t *salt, uint_t salt_len, uint8_t *key_material,
    uint_t km_len, uint8_t *out_buf)
{
	crypto_key_t key;

	/* initialize the salt as a crypto key */
	key.ck_length = CRYPTO_BYTES2BITS(salt_len);
	key.ck_data = salt;

	crypto_mac(&key, key_material, km_len, out_buf, SHA512_DIGEST_LENGTH);

	return (0);
}

static int
hkdf_sha512_expand(uint8_t *extract_key, uint8_t *info, uint_t info_len,
    uint8_t *out_buf, uint_t out_len)
{
	struct hmac_ctx ctx;
	crypto_key_t key;
	uint_t i, T_len = 0, pos = 0;
	uint8_t c;
	uint_t N = (out_len + SHA512_DIGEST_LENGTH) / SHA512_DIGEST_LENGTH;
	uint8_t T[SHA512_DIGEST_LENGTH];

	if (N > 255)
		return (SET_ERROR(EINVAL));

	/* initialize the salt as a crypto key */
	key.ck_length = CRYPTO_BYTES2BITS(SHA512_DIGEST_LENGTH);
	key.ck_data = extract_key;

	for (i = 1; i <= N; i++) {
		c = i;

		crypto_mac_init(&ctx, &key);
		crypto_mac_update(&ctx, T, T_len);
		crypto_mac_update(&ctx, info, info_len);
		crypto_mac_update(&ctx, &c, 1);
		crypto_mac_final(&ctx, T, SHA512_DIGEST_LENGTH);
		memcpy(out_buf + pos, T,
		    (i != N) ? SHA512_DIGEST_LENGTH : (out_len - pos));
		pos += SHA512_DIGEST_LENGTH;
	}

	return (0);
}

/*
 * HKDF is designed to be a relatively fast function for deriving keys from a
 * master key + a salt. We use this function to generate new encryption keys
 * so as to avoid hitting the cryptographic limits of the underlying
 * encryption modes. Note that, for the sake of deriving encryption keys, the
 * info parameter is called the "salt" everywhere else in the code.
 */
int
hkdf_sha512(uint8_t *key_material, uint_t km_len, uint8_t *salt,
    uint_t salt_len, uint8_t *info, uint_t info_len, uint8_t *output_key,
    uint_t out_len)
{
	int ret;
	uint8_t extract_key[SHA512_DIGEST_LENGTH];

	ret = hkdf_sha512_extract(salt, salt_len, key_material, km_len,
	    extract_key);
	if (ret != 0)
		return (ret);

	ret = hkdf_sha512_expand(extract_key, info, info_len, output_key,
	    out_len);
	if (ret != 0)
		return (ret);

	return (0);
}