esp-idf/components/wpa_supplicant/src/crypto/aes-unwrap.c

/*
 * AES key unwrap (128-bit KEK, RFC3394)
 *
 * Copyright (c) 2003-2007, Jouni Malinen <j@w1.fi>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * Alternatively, this software may be distributed under the terms of BSD
 * license.
 *
 * See README and COPYING for more details.
 */
/*
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Hardware crypto support Copyright 2017-2019 Espressif Systems (Shanghai) PTE LTD
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "utils/includes.h"

#include "utils/common.h"
#ifdef USE_MBEDTLS_CRYPTO
#include "mbedtls/aes.h"
#else /* USE_MBEDTLS_CRYPTO */
#include "aes.h"
#include "aes_wrap.h"
#endif /* USE_MBEDTLS_CRYPTO */

/**
 * aes_unwrap - Unwrap key with AES Key Wrap Algorithm (128-bit KEK) (RFC3394)
 * @kek: Key encryption key (KEK)
 * @n: Length of the plaintext key in 64-bit units; e.g., 2 = 128-bit = 16
 * bytes
 * @cipher: Wrapped key to be unwrapped, (n + 1) * 64 bits
 * @plain: Plaintext key, n * 64 bits
 * Returns: 0 on success, -1 on failure (e.g., integrity verification failed)
 */
int
aes_unwrap(const u8 *kek, int n, const u8 *cipher, u8 *plain)
{
	u8 a[8], *r, b[16];
	int i, j;
#ifdef USE_MBEDTLS_CRYPTO
	int32_t ret = 0;
	mbedtls_aes_context ctx;
#else /* USE_MBEDTLS_CRYPTO */
	void *ctx;
#endif /* USE_MBEDTLS_CRYPTO */

	/* 1) Initialize variables. */
	os_memcpy(a, cipher, 8);
	r = plain;
	os_memcpy(r, cipher + 8, 8 * n);

#ifdef USE_MBEDTLS_CRYPTO
	mbedtls_aes_init(&ctx);
	ret = mbedtls_aes_setkey_dec(&ctx, kek, 128);
	if (ret < 0) {
		mbedtls_aes_free(&ctx);
		return ret;
	}
#else /* USE_MBEDTLS_CRYPTO */
	ctx = aes_decrypt_init(kek, 16);
	if (ctx == NULL)
		return -1;
#endif /* USE_MBEDTLS_CRYPTO */

	/* 2) Compute intermediate values.
	 * For j = 5 to 0
	 *     For i = n to 1
	 *         B = AES-1(K, (A ^ t) | R[i]) where t = n*j+i
	 *         A = MSB(64, B)
	 *         R[i] = LSB(64, B)
	 */
	for (j = 5; j >= 0; j--) {
		r = plain + (n - 1) * 8;
		for (i = n; i >= 1; i--) {
			os_memcpy(b, a, 8);
			b[7] ^= n * j + i;

			os_memcpy(b + 8, r, 8);
#ifdef USE_MBEDTLS_CRYPTO
			ret = mbedtls_internal_aes_decrypt(&ctx, b, b);
#else /* USE_MBEDTLS_CRYPTO */
			aes_decrypt(ctx, b, b);
#endif /* USE_MBEDTLS_CRYPTO */
			os_memcpy(a, b, 8);
			os_memcpy(r, b + 8, 8);
			r -= 8;
		}
	}
#ifdef USE_MBEDTLS_CRYPTO
	mbedtls_aes_free(&ctx);
#else /* USE_MBEDTLS_CRYPTO */
	aes_decrypt_deinit(ctx);
#endif /* USE_MBEDTLS_CRYPTO */

	/* 3) Output results.
	 *
	 * These are already in @plain due to the location of temporary
	 * variables. Just verify that the IV matches with the expected value.
	 */
	for (i = 0; i < 8; i++) {
		if (a[i] != 0xa6)
			return -1;
	}

	return 0;
}