1 /* 2 * AES key unwrap (128-bit KEK, RFC3394) 3 * 4 * Copyright (c) 2003-2007, Jouni Malinen <j (at) w1.fi> 5 * 6 * This program is free software; you can redistribute it and/or modify 7 * it under the terms of the GNU General Public License version 2 as 8 * published by the Free Software Foundation. 9 * 10 * Alternatively, this software may be distributed under the terms of BSD 11 * license. 12 * 13 * See README and COPYING for more details. 14 */ 15 16 #include "includes.h" 17 18 #include "common.h" 19 #include "aes.h" 20 #include "aes_wrap.h" 21 22 /** 23 * aes_unwrap - Unwrap key with AES Key Wrap Algorithm (128-bit KEK) (RFC3394) 24 * @kek: Key encryption key (KEK) 25 * @n: Length of the plaintext key in 64-bit units; e.g., 2 = 128-bit = 16 26 * bytes 27 * @cipher: Wrapped key to be unwrapped, (n + 1) * 64 bits 28 * @plain: Plaintext key, n * 64 bits 29 * Returns: 0 on success, -1 on failure (e.g., integrity verification failed) 30 */ 31 int aes_unwrap(const u8 *kek, int n, const u8 *cipher, u8 *plain) 32 { 33 u8 a[8], *r, b[16]; 34 int i, j; 35 void *ctx; 36 37 /* 1) Initialize variables. */ 38 os_memcpy(a, cipher, 8); 39 r = plain; 40 os_memcpy(r, cipher + 8, 8 * n); 41 42 ctx = aes_decrypt_init(kek, 16); 43 if (ctx == NULL) 44 return -1; 45 46 /* 2) Compute intermediate values. 47 * For j = 5 to 0 48 * For i = n to 1 49 * B = AES-1(K, (A ^ t) | R[i]) where t = n*j+i 50 * A = MSB(64, B) 51 * R[i] = LSB(64, B) 52 */ 53 for (j = 5; j >= 0; j--) { 54 r = plain + (n - 1) * 8; 55 for (i = n; i >= 1; i--) { 56 os_memcpy(b, a, 8); 57 b[7] ^= n * j + i; 58 59 os_memcpy(b + 8, r, 8); 60 aes_decrypt(ctx, b, b); 61 os_memcpy(a, b, 8); 62 os_memcpy(r, b + 8, 8); 63 r -= 8; 64 } 65 } 66 aes_decrypt_deinit(ctx); 67 68 /* 3) Output results. 69 * 70 * These are already in @plain due to the location of temporary 71 * variables. Just verify that the IV matches with the expected value. 72 */ 73 for (i = 0; i < 8; i++) { 74 if (a[i] != 0xa6) 75 return -1; 76 } 77 78 return 0; 79 } 80
