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crc32c.c

/* 
 * Cryptographic API.
 *
 * CRC32C chksum
 *
 * This module file is a wrapper to invoke the lib/crc32c routines.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation; either version 2 of the License, or (at your option) 
 * any later version.
 *
 */
#include <linux/init.h>
#include <linux/module.h>
#include <linux/string.h>
#include <linux/crypto.h>
#include <linux/crc32c.h>
#include <linux/kernel.h>

#define CHKSUM_BLOCK_SIZE     32
#define CHKSUM_DIGEST_SIZE    4

struct chksum_ctx {
      u32 crc;
      u32 key;
};

/*
 * Steps through buffer one byte at at time, calculates reflected 
 * crc using table.
 */

static void chksum_init(struct crypto_tfm *tfm)
{
      struct chksum_ctx *mctx = crypto_tfm_ctx(tfm);

      mctx->crc = mctx->key;
}

/*
 * Setting the seed allows arbitrary accumulators and flexible XOR policy
 * If your algorithm starts with ~0, then XOR with ~0 before you set
 * the seed.
 */
static int chksum_setkey(struct crypto_tfm *tfm, const u8 *key,
                   unsigned int keylen)
{
      struct chksum_ctx *mctx = crypto_tfm_ctx(tfm);

      if (keylen != sizeof(mctx->crc)) {
            tfm->crt_flags |= CRYPTO_TFM_RES_BAD_KEY_LEN;
            return -EINVAL;
      }
      mctx->key = le32_to_cpu(*(__le32 *)key);
      return 0;
}

static void chksum_update(struct crypto_tfm *tfm, const u8 *data,
                    unsigned int length)
{
      struct chksum_ctx *mctx = crypto_tfm_ctx(tfm);

      mctx->crc = crc32c(mctx->crc, data, length);
}

static void chksum_final(struct crypto_tfm *tfm, u8 *out)
{
      struct chksum_ctx *mctx = crypto_tfm_ctx(tfm);
      
      *(__le32 *)out = ~cpu_to_le32(mctx->crc);
}

static int crc32c_cra_init(struct crypto_tfm *tfm)
{
      struct chksum_ctx *mctx = crypto_tfm_ctx(tfm);

      mctx->key = ~0;
      return 0;
}

static struct crypto_alg alg = {
      .cra_name   =     "crc32c",
      .cra_flags  =     CRYPTO_ALG_TYPE_DIGEST,
      .cra_blocksize    =     CHKSUM_BLOCK_SIZE,
      .cra_ctxsize      =     sizeof(struct chksum_ctx),
      .cra_module =     THIS_MODULE,
      .cra_list   =     LIST_HEAD_INIT(alg.cra_list),
      .cra_init   =     crc32c_cra_init,
      .cra_u            =     {
            .digest = {
                   .dia_digestsize= CHKSUM_DIGEST_SIZE,
                   .dia_setkey      =     chksum_setkey,
                   .dia_init        =     chksum_init,
                   .dia_update      =     chksum_update,
                   .dia_final       =     chksum_final
             }
      }
};

static int __init init(void)
{
      return crypto_register_alg(&alg);
}

static void __exit fini(void)
{
      crypto_unregister_alg(&alg);
}

module_init(init);
module_exit(fini);

MODULE_AUTHOR("Clay Haapala <chaapala@cisco.com>");
MODULE_DESCRIPTION("CRC32c (Castagnoli) calculations wrapper for lib/crc32c");
MODULE_LICENSE("GPL");

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