aes-omac1.c

Go to the documentation of this file.

/*
 * One-key CBC MAC (OMAC1) hash with AES-128
 *
 * Copyright (c) 2003-2007, Jouni Malinen <j@w1.fi>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * Alternatively, this software may be distributed under the terms of BSD
 * license.
 *
 * See README and COPYING for more details.
 */

#include "includes.h"

#include "common.h"
#include "aes.h"
#include "aes_wrap.h"

static void gf_mulx(u8 *pad)
{
        int i, carry;

        carry = pad[0] & 0x80;
        for (i = 0; i < AES_BLOCK_SIZE - 1; i++)
                pad[i] = (pad[i] << 1) | (pad[i + 1] >> 7);
        pad[AES_BLOCK_SIZE - 1] <<= 1;
        if (carry)
                pad[AES_BLOCK_SIZE - 1] ^= 0x87;
}


int omac1_aes_128_vector(const u8 *key, size_t num_elem,
                         const u8 *addr[], const size_t *len, u8 *mac)
{
        void *ctx;
        u8 cbc[AES_BLOCK_SIZE], pad[AES_BLOCK_SIZE];
        const u8 *pos, *end;
        size_t i, e, left, total_len;

        ctx = aes_encrypt_init(key, 16);
        if (ctx == NULL)
                return -1;
        os_memset(cbc, 0, AES_BLOCK_SIZE);

        total_len = 0;
        for (e = 0; e < num_elem; e++)
                total_len += len[e];
        left = total_len;

        e = 0;
        pos = addr[0];
        end = pos + len[0];

        while (left >= AES_BLOCK_SIZE) {
                for (i = 0; i < AES_BLOCK_SIZE; i++) {
                        cbc[i] ^= *pos++;
                        if (pos >= end) {
                                e++;
                                pos = addr[e];
                                end = pos + len[e];
                        }
                }
                if (left > AES_BLOCK_SIZE)
                        aes_encrypt(ctx, cbc, cbc);
                left -= AES_BLOCK_SIZE;
        }

        os_memset(pad, 0, AES_BLOCK_SIZE);
        aes_encrypt(ctx, pad, pad);
        gf_mulx(pad);

        if (left || total_len == 0) {
                for (i = 0; i < left; i++) {
                        cbc[i] ^= *pos++;
                        if (pos >= end) {
                                e++;
                                pos = addr[e];
                                end = pos + len[e];
                        }
                }
                cbc[left] ^= 0x80;
                gf_mulx(pad);
        }

        for (i = 0; i < AES_BLOCK_SIZE; i++)
                pad[i] ^= cbc[i];
        aes_encrypt(ctx, pad, mac);
        aes_encrypt_deinit(ctx);
        return 0;
}


int omac1_aes_128(const u8 *key, const u8 *data, size_t data_len, u8 *mac)
{
        return omac1_aes_128_vector(key, 1, &data, &data_len, mac);
}