mirror of
https://github.com/vanhoefm/fragattacks.git
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79 lines
1.8 KiB
C
79 lines
1.8 KiB
C
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/*
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* AES key unwrap (128-bit KEK, RFC3394)
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*
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* Copyright (c) 2003-2007, Jouni Malinen <j@w1.fi>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*
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* Alternatively, this software may be distributed under the terms of BSD
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* license.
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*
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* See README and COPYING for more details.
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*/
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#include "includes.h"
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#include "common.h"
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#include "aes_i.h"
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/**
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* aes_unwrap - Unwrap key with AES Key Wrap Algorithm (128-bit KEK) (RFC3394)
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* @kek: Key encryption key (KEK)
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* @n: Length of the plaintext key in 64-bit units; e.g., 2 = 128-bit = 16
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* bytes
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* @cipher: Wrapped key to be unwrapped, (n + 1) * 64 bits
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* @plain: Plaintext key, n * 64 bits
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* Returns: 0 on success, -1 on failure (e.g., integrity verification failed)
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*/
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int aes_unwrap(const u8 *kek, int n, const u8 *cipher, u8 *plain)
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{
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u8 a[8], *r, b[16];
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int i, j;
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void *ctx;
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/* 1) Initialize variables. */
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os_memcpy(a, cipher, 8);
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r = plain;
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os_memcpy(r, cipher + 8, 8 * n);
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ctx = aes_decrypt_init(kek, 16);
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if (ctx == NULL)
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return -1;
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/* 2) Compute intermediate values.
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* For j = 5 to 0
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* For i = n to 1
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* B = AES-1(K, (A ^ t) | R[i]) where t = n*j+i
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* A = MSB(64, B)
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* R[i] = LSB(64, B)
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*/
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for (j = 5; j >= 0; j--) {
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r = plain + (n - 1) * 8;
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for (i = n; i >= 1; i--) {
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os_memcpy(b, a, 8);
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b[7] ^= n * j + i;
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os_memcpy(b + 8, r, 8);
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aes_decrypt(ctx, b, b);
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os_memcpy(a, b, 8);
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os_memcpy(r, b + 8, 8);
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r -= 8;
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}
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}
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aes_decrypt_deinit(ctx);
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/* 3) Output results.
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*
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* These are already in @plain due to the location of temporary
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* variables. Just verify that the IV matches with the expected value.
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*/
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for (i = 0; i < 8; i++) {
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if (a[i] != 0xa6)
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return -1;
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}
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return 0;
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}
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