hostapd/src/crypto/aes-unwrap.c

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/*
* 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.
*/
#include "includes.h"
#include "common.h"
#include "aes.h"
/**
* 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;
void *ctx;
/* 1) Initialize variables. */
os_memcpy(a, cipher, 8);
r = plain;
os_memcpy(r, cipher + 8, 8 * n);
ctx = aes_decrypt_init(kek, 16);
if (ctx == NULL)
return -1;
/* 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);
aes_decrypt(ctx, b, b);
os_memcpy(a, b, 8);
os_memcpy(r, b + 8, 8);
r -= 8;
}
}
aes_decrypt_deinit(ctx);
/* 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;
}