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