1 /* 2 * AES key unwrap (RFC3394) 3 * 4 * Copyright (c) 2003-2007, Jouni Malinen <j (at) 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 (RFC3394) 18 * @kek: Key encryption key (KEK) 19 * @kek_len: Length of KEK in octets 20 * @n: Length of the plaintext key in 64-bit units; e.g., 2 = 128-bit = 16 21 * bytes 22 * @cipher: Wrapped key to be unwrapped, (n + 1) * 64 bits 23 * @plain: Plaintext key, n * 64 bits 24 * Returns: 0 on success, -1 on failure (e.g., integrity verification failed) 25 */ 26 int aes_unwrap(const u8 *kek, size_t kek_len, int n, const u8 *cipher, 27 u8 *plain) 28 { 29 u8 a[8], *r, b[AES_BLOCK_SIZE]; 30 int i, j; 31 void *ctx; 32 unsigned int t; 33 34 /* 1) Initialize variables. */ 35 os_memcpy(a, cipher, 8); 36 r = plain; 37 os_memcpy(r, cipher + 8, 8 * n); 38 39 ctx = aes_decrypt_init(kek, kek_len); 40 if (ctx == NULL) 41 return -1; 42 43 /* 2) Compute intermediate values. 44 * For j = 5 to 0 45 * For i = n to 1 46 * B = AES-1(K, (A ^ t) | R[i]) where t = n*j+i 47 * A = MSB(64, B) 48 * R[i] = LSB(64, B) 49 */ 50 for (j = 5; j >= 0; j--) { 51 r = plain + (n - 1) * 8; 52 for (i = n; i >= 1; i--) { 53 os_memcpy(b, a, 8); 54 t = n * j + i; 55 b[7] ^= t; 56 b[6] ^= t >> 8; 57 b[5] ^= t >> 16; 58 b[4] ^= t >> 24; 59 60 os_memcpy(b + 8, r, 8); 61 aes_decrypt(ctx, b, b); 62 os_memcpy(a, b, 8); 63 os_memcpy(r, b + 8, 8); 64 r -= 8; 65 } 66 } 67 aes_decrypt_deinit(ctx); 68 69 /* 3) Output results. 70 * 71 * These are already in @plain due to the location of temporary 72 * variables. Just verify that the IV matches with the expected value. 73 */ 74 for (i = 0; i < 8; i++) { 75 if (a[i] != 0xa6) 76 return -1; 77 } 78 79 return 0; 80 } 81
