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| /*
| * AES key unwrap (RFC3394)
| *
| * Copyright (c) 2003-2007, Jouni Malinen <j@w1.fi>
| *
| * This software may be distributed under the terms of the BSD license.
| * See README for more details.
| */
|
| #include "includes.h"
|
| #include "common.h"
| #include "aes.h"
| #include "aes_wrap.h"
|
| /**
| * aes_unwrap - Unwrap key with AES Key Wrap Algorithm (RFC3394)
| * @kek: Key encryption key (KEK)
| * @kek_len: Length of KEK in octets
| * @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, size_t kek_len, int n, const u8 *cipher,
| u8 *plain)
| {
| u8 a[8], *r, b[AES_BLOCK_SIZE];
| int i, j;
| void *ctx;
| unsigned int t;
|
| /* 1) Initialize variables. */
| os_memcpy(a, cipher, 8);
| r = plain;
| os_memcpy(r, cipher + 8, 8 * n);
|
| ctx = aes_decrypt_init(kek, kek_len);
| 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);
| t = n * j + i;
| b[7] ^= t;
| b[6] ^= t >> 8;
| b[5] ^= t >> 16;
| b[4] ^= t >> 24;
|
| 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;
| }
|
|
