aes_cmac.c

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/*
 * AES-128-CMAC with TLen 16 for IEEE 802.11w BIP
 * Copyright 2008, Jouni Malinen <[email protected]>
 *
 * 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.
 */

#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/crypto.h>
#include <linux/err.h>
#include <crypto/aes.h>

#include <net/mac80211.h>
#include "key.h"
#include "aes_cmac.h"

#define AES_CMAC_KEY_LEN 16
#define CMAC_TLEN 8 /* CMAC TLen = 64 bits (8 octets) */
#define AAD_LEN 20


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;
}


static void aes_128_cmac_vector(struct crypto_cipher *tfm, size_t num_elem,
                const u8 *addr[], const size_t *len, u8 *mac)
{
    u8 cbc[AES_BLOCK_SIZE], pad[AES_BLOCK_SIZE];
    const u8 *pos, *end;
    size_t i, e, left, total_len;

    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)
            crypto_cipher_encrypt_one(tfm, cbc, cbc);
        left -= AES_BLOCK_SIZE;
    }

    memset(pad, 0, AES_BLOCK_SIZE);
    crypto_cipher_encrypt_one(tfm, 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];
    crypto_cipher_encrypt_one(tfm, pad, pad);
    memcpy(mac, pad, CMAC_TLEN);
}


void ieee80211_aes_cmac(struct crypto_cipher *tfm, const u8 *aad,
            const u8 *data, size_t data_len, u8 *mic)
{
    const u8 *addr[3];
    size_t len[3];
    u8 zero[CMAC_TLEN];

    memset(zero, 0, CMAC_TLEN);
    addr[0] = aad;
    len[0] = AAD_LEN;
    addr[1] = data;
    len[1] = data_len - CMAC_TLEN;
    addr[2] = zero;
    len[2] = CMAC_TLEN;

    aes_128_cmac_vector(tfm, 3, addr, len, mic);
}


struct crypto_cipher * ieee80211_aes_cmac_key_setup(const u8 key[])
{
    struct crypto_cipher *tfm;

    tfm = crypto_alloc_cipher("aes", 0, CRYPTO_ALG_ASYNC);
    if (!IS_ERR(tfm))
        crypto_cipher_setkey(tfm, key, AES_CMAC_KEY_LEN);

    return tfm;
}


void ieee80211_aes_cmac_key_free(struct crypto_cipher *tfm)
{
    crypto_free_cipher(tfm);
}