michael_mic.c

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/*
 * Cryptographic API
 *
 * Michael MIC (IEEE 802.11i/TKIP) keyed digest
 *
 * Copyright (c) 2004 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 <crypto/internal/hash.h>
#include <asm/byteorder.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/string.h>
#include <linux/types.h>


struct michael_mic_ctx {
    u32 l, r;
};

struct michael_mic_desc_ctx {
    u8 pending[4];
    size_t pending_len;

    u32 l, r;
};

static inline u32 xswap(u32 val)
{
    return ((val & 0x00ff00ff) << 8) | ((val & 0xff00ff00) >> 8);
}


#define michael_block(l, r) \
do {                \
    r ^= rol32(l, 17);  \
    l += r;         \
    r ^= xswap(l);      \
    l += r;         \
    r ^= rol32(l, 3);   \
    l += r;         \
    r ^= ror32(l, 2);   \
    l += r;         \
} while (0)


static int michael_init(struct shash_desc *desc)
{
    struct michael_mic_desc_ctx *mctx = shash_desc_ctx(desc);
    struct michael_mic_ctx *ctx = crypto_shash_ctx(desc->tfm);
    mctx->pending_len = 0;
    mctx->l = ctx->l;
    mctx->r = ctx->r;

    return 0;
}


static int michael_update(struct shash_desc *desc, const u8 *data,
               unsigned int len)
{
    struct michael_mic_desc_ctx *mctx = shash_desc_ctx(desc);
    const __le32 *src;

    if (mctx->pending_len) {
        int flen = 4 - mctx->pending_len;
        if (flen > len)
            flen = len;
        memcpy(&mctx->pending[mctx->pending_len], data, flen);
        mctx->pending_len += flen;
        data += flen;
        len -= flen;

        if (mctx->pending_len < 4)
            return 0;

        src = (const __le32 *)mctx->pending;
        mctx->l ^= le32_to_cpup(src);
        michael_block(mctx->l, mctx->r);
        mctx->pending_len = 0;
    }

    src = (const __le32 *)data;

    while (len >= 4) {
        mctx->l ^= le32_to_cpup(src++);
        michael_block(mctx->l, mctx->r);
        len -= 4;
    }

    if (len > 0) {
        mctx->pending_len = len;
        memcpy(mctx->pending, src, len);
    }

    return 0;
}


static int michael_final(struct shash_desc *desc, u8 *out)
{
    struct michael_mic_desc_ctx *mctx = shash_desc_ctx(desc);
    u8 *data = mctx->pending;
    __le32 *dst = (__le32 *)out;

    /* Last block and padding (0x5a, 4..7 x 0) */
    switch (mctx->pending_len) {
    case 0:
        mctx->l ^= 0x5a;
        break;
    case 1:
        mctx->l ^= data[0] | 0x5a00;
        break;
    case 2:
        mctx->l ^= data[0] | (data[1] << 8) | 0x5a0000;
        break;
    case 3:
        mctx->l ^= data[0] | (data[1] << 8) | (data[2] << 16) |
            0x5a000000;
        break;
    }
    michael_block(mctx->l, mctx->r);
    /* l ^= 0; */
    michael_block(mctx->l, mctx->r);

    dst[0] = cpu_to_le32(mctx->l);
    dst[1] = cpu_to_le32(mctx->r);

    return 0;
}


static int michael_setkey(struct crypto_shash *tfm, const u8 *key,
              unsigned int keylen)
{
    struct michael_mic_ctx *mctx = crypto_shash_ctx(tfm);

    const __le32 *data = (const __le32 *)key;

    if (keylen != 8) {
        crypto_shash_set_flags(tfm, CRYPTO_TFM_RES_BAD_KEY_LEN);
        return -EINVAL;
    }

    mctx->l = le32_to_cpu(data[0]);
    mctx->r = le32_to_cpu(data[1]);
    return 0;
}

static struct shash_alg alg = {
    .digestsize     =   8,
    .setkey         =   michael_setkey,
    .init           =   michael_init,
    .update         =   michael_update,
    .final          =   michael_final,
    .descsize       =   sizeof(struct michael_mic_desc_ctx),
    .base           =   {
        .cra_name       =   "michael_mic",
        .cra_blocksize      =   8,
        .cra_alignmask      =   3,
        .cra_ctxsize        =   sizeof(struct michael_mic_ctx),
        .cra_module     =   THIS_MODULE,
    }
};

static int __init michael_mic_init(void)
{
    return crypto_register_shash(&alg);
}


static void __exit michael_mic_exit(void)
{
    crypto_unregister_shash(&alg);
}


module_init(michael_mic_init);
module_exit(michael_mic_exit);

MODULE_LICENSE("GPL v2");
MODULE_DESCRIPTION("Michael MIC");
MODULE_AUTHOR("Jouni Malinen <[email protected]>");