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michael_mic.c

/*
 * Cryptographic API
 *
 * Michael MIC (IEEE 802.11i/TKIP) keyed digest
 *
 * Copyright (c) 2004 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.
 */

#include <asm/byteorder.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/string.h>
#include <linux/crypto.h>
#include <linux/types.h>


struct michael_mic_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 void michael_init(struct crypto_tfm *tfm)
{
      struct michael_mic_ctx *mctx = crypto_tfm_ctx(tfm);
      mctx->pending_len = 0;
}


static void michael_update(struct crypto_tfm *tfm, const u8 *data,
                     unsigned int len)
{
      struct michael_mic_ctx *mctx = crypto_tfm_ctx(tfm);
      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;

            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);
      }
}


static void michael_final(struct crypto_tfm *tfm, u8 *out)
{
      struct michael_mic_ctx *mctx = crypto_tfm_ctx(tfm);
      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);
}


static int michael_setkey(struct crypto_tfm *tfm, const u8 *key,
                    unsigned int keylen)
{
      struct michael_mic_ctx *mctx = crypto_tfm_ctx(tfm);
      const __le32 *data = (const __le32 *)key;

      if (keylen != 8) {
            tfm->crt_flags |= 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 crypto_alg michael_mic_alg = {
      .cra_name   = "michael_mic",
      .cra_flags  = CRYPTO_ALG_TYPE_DIGEST,
      .cra_blocksize    = 8,
      .cra_ctxsize      = sizeof(struct michael_mic_ctx),
      .cra_module = THIS_MODULE,
      .cra_alignmask    = 3,
      .cra_list   = LIST_HEAD_INIT(michael_mic_alg.cra_list),
      .cra_u            = { .digest = {
      .dia_digestsize   = 8,
      .dia_init   = michael_init,
      .dia_update = michael_update,
      .dia_final  = michael_final,
      .dia_setkey = michael_setkey } }
};


static int __init michael_mic_init(void)
{
      return crypto_register_alg(&michael_mic_alg);
}


static void __exit michael_mic_exit(void)
{
      crypto_unregister_alg(&michael_mic_alg);
}


module_init(michael_mic_init);
module_exit(michael_mic_exit);

MODULE_LICENSE("GPL v2");
MODULE_DESCRIPTION("Michael MIC");
MODULE_AUTHOR("Jouni Malinen <j@w1.fi>");

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