aes_ccm.c

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/*
 * Copyright 2003-2004, Instant802 Networks, Inc.
 * Copyright 2005-2006, Devicescape Software, Inc.
 *
 * 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_ccm.h"

static void aes_ccm_prepare(struct crypto_cipher *tfm, u8 *scratch, u8 *a)
{
    int i;
    u8 *b_0, *aad, *b, *s_0;

    b_0 = scratch + 3 * AES_BLOCK_SIZE;
    aad = scratch + 4 * AES_BLOCK_SIZE;
    b = scratch;
    s_0 = scratch + AES_BLOCK_SIZE;

    crypto_cipher_encrypt_one(tfm, b, b_0);

    /* Extra Authenticate-only data (always two AES blocks) */
    for (i = 0; i < AES_BLOCK_SIZE; i++)
        aad[i] ^= b[i];
    crypto_cipher_encrypt_one(tfm, b, aad);

    aad += AES_BLOCK_SIZE;

    for (i = 0; i < AES_BLOCK_SIZE; i++)
        aad[i] ^= b[i];
    crypto_cipher_encrypt_one(tfm, a, aad);

    /* Mask out bits from auth-only-b_0 */
    b_0[0] &= 0x07;

    /* S_0 is used to encrypt T (= MIC) */
    b_0[14] = 0;
    b_0[15] = 0;
    crypto_cipher_encrypt_one(tfm, s_0, b_0);
}


void ieee80211_aes_ccm_encrypt(struct crypto_cipher *tfm, u8 *scratch,
                   u8 *data, size_t data_len,
                   u8 *cdata, u8 *mic)
{
    int i, j, last_len, num_blocks;
    u8 *pos, *cpos, *b, *s_0, *e, *b_0;

    b = scratch;
    s_0 = scratch + AES_BLOCK_SIZE;
    e = scratch + 2 * AES_BLOCK_SIZE;
    b_0 = scratch + 3 * AES_BLOCK_SIZE;

    num_blocks = DIV_ROUND_UP(data_len, AES_BLOCK_SIZE);
    last_len = data_len % AES_BLOCK_SIZE;
    aes_ccm_prepare(tfm, scratch, b);

    /* Process payload blocks */
    pos = data;
    cpos = cdata;
    for (j = 1; j <= num_blocks; j++) {
        int blen = (j == num_blocks && last_len) ?
            last_len : AES_BLOCK_SIZE;

        /* Authentication followed by encryption */
        for (i = 0; i < blen; i++)
            b[i] ^= pos[i];
        crypto_cipher_encrypt_one(tfm, b, b);

        b_0[14] = (j >> 8) & 0xff;
        b_0[15] = j & 0xff;
        crypto_cipher_encrypt_one(tfm, e, b_0);
        for (i = 0; i < blen; i++)
            *cpos++ = *pos++ ^ e[i];
    }

    for (i = 0; i < CCMP_MIC_LEN; i++)
        mic[i] = b[i] ^ s_0[i];
}


int ieee80211_aes_ccm_decrypt(struct crypto_cipher *tfm, u8 *scratch,
                  u8 *cdata, size_t data_len, u8 *mic, u8 *data)
{
    int i, j, last_len, num_blocks;
    u8 *pos, *cpos, *b, *s_0, *a, *b_0;

    b = scratch;
    s_0 = scratch + AES_BLOCK_SIZE;
    a = scratch + 2 * AES_BLOCK_SIZE;
    b_0 = scratch + 3 * AES_BLOCK_SIZE;

    num_blocks = DIV_ROUND_UP(data_len, AES_BLOCK_SIZE);
    last_len = data_len % AES_BLOCK_SIZE;
    aes_ccm_prepare(tfm, scratch, a);

    /* Process payload blocks */
    cpos = cdata;
    pos = data;
    for (j = 1; j <= num_blocks; j++) {
        int blen = (j == num_blocks && last_len) ?
            last_len : AES_BLOCK_SIZE;

        /* Decryption followed by authentication */
        b_0[14] = (j >> 8) & 0xff;
        b_0[15] = j & 0xff;
        crypto_cipher_encrypt_one(tfm, b, b_0);
        for (i = 0; i < blen; i++) {
            *pos = *cpos++ ^ b[i];
            a[i] ^= *pos++;
        }
        crypto_cipher_encrypt_one(tfm, a, a);
    }

    for (i = 0; i < CCMP_MIC_LEN; i++) {
        if ((mic[i] ^ s_0[i]) != a[i])
            return -1;
    }

    return 0;
}


struct crypto_cipher *ieee80211_aes_key_setup_encrypt(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, ALG_CCMP_KEY_LEN);

    return tfm;
}


void ieee80211_aes_key_free(struct crypto_cipher *tfm)
{
    crypto_free_cipher(tfm);
}