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lrw.c

/* LRW: as defined by Cyril Guyot in
 *    http://grouper.ieee.org/groups/1619/email/pdf00017.pdf
 *
 * Copyright (c) 2006 Rik Snel <rsnel@cube.dyndns.org>
 *
 * Based om ecb.c
 * Copyright (c) 2006 Herbert Xu <herbert@gondor.apana.org.au>
 *
 * 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.
 */
/* This implementation is checked against the test vectors in the above
 * document and by a test vector provided by Ken Buchanan at
 * http://www.mail-archive.com/stds-p1619@listserv.ieee.org/msg00173.html
 *
 * The test vectors are included in the testing module tcrypt.[ch] */
#include <crypto/algapi.h>
#include <linux/err.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/scatterlist.h>
#include <linux/slab.h>

#include <crypto/b128ops.h>
#include <crypto/gf128mul.h>

struct priv {
      struct crypto_cipher *child;
      /* optimizes multiplying a random (non incrementing, as at the
       * start of a new sector) value with key2, we could also have
       * used 4k optimization tables or no optimization at all. In the
       * latter case we would have to store key2 here */
      struct gf128mul_64k *table;
      /* stores:
       *  key2*{ 0,0,...0,0,0,0,1 }, key2*{ 0,0,...0,0,0,1,1 },
       *  key2*{ 0,0,...0,0,1,1,1 }, key2*{ 0,0,...0,1,1,1,1 }
       *  key2*{ 0,0,...1,1,1,1,1 }, etc
       * needed for optimized multiplication of incrementing values
       * with key2 */
      be128 mulinc[128];
};

static inline void setbit128_bbe(void *b, int bit)
{
      __set_bit(bit ^ 0x78, b);
}

static int setkey(struct crypto_tfm *parent, const u8 *key,
              unsigned int keylen)
{
      struct priv *ctx = crypto_tfm_ctx(parent);
      struct crypto_cipher *child = ctx->child;
      int err, i;
      be128 tmp = { 0 };
      int bsize = crypto_cipher_blocksize(child);

      crypto_cipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
      crypto_cipher_set_flags(child, crypto_tfm_get_flags(parent) &
                               CRYPTO_TFM_REQ_MASK);
      if ((err = crypto_cipher_setkey(child, key, keylen - bsize)))
            return err;
      crypto_tfm_set_flags(parent, crypto_cipher_get_flags(child) &
                             CRYPTO_TFM_RES_MASK);

      if (ctx->table)
            gf128mul_free_64k(ctx->table);

      /* initialize multiplication table for Key2 */
      ctx->table = gf128mul_init_64k_bbe((be128 *)(key + keylen - bsize));
      if (!ctx->table)
            return -ENOMEM;

      /* initialize optimization table */
      for (i = 0; i < 128; i++) {
            setbit128_bbe(&tmp, i);
            ctx->mulinc[i] = tmp;
            gf128mul_64k_bbe(&ctx->mulinc[i], ctx->table);
      }

      return 0;
}

struct sinfo {
      be128 t;
      struct crypto_tfm *tfm;
      void (*fn)(struct crypto_tfm *, u8 *, const u8 *);
};

static inline void inc(be128 *iv)
{
      if (!(iv->b = cpu_to_be64(be64_to_cpu(iv->b) + 1)))
            iv->a = cpu_to_be64(be64_to_cpu(iv->a) + 1);
}

static inline void lrw_round(struct sinfo *s, void *dst, const void *src)
{
      be128_xor(dst, &s->t, src);         /* PP <- T xor P */
      s->fn(s->tfm, dst, dst);            /* CC <- E(Key2,PP) */
      be128_xor(dst, dst, &s->t);         /* C <- T xor CC */
}

/* this returns the number of consequative 1 bits starting
 * from the right, get_index128(00 00 00 00 00 00 ... 00 00 10 FB) = 2 */
static inline int get_index128(be128 *block)
{
      int x;
      __be32 *p = (__be32 *) block;

      for (p += 3, x = 0; x < 128; p--, x += 32) {
            u32 val = be32_to_cpup(p);

            if (!~val)
                  continue;

            return x + ffz(val);
      }

      return x;
}

static int crypt(struct blkcipher_desc *d,
             struct blkcipher_walk *w, struct priv *ctx,
             void (*fn)(struct crypto_tfm *, u8 *, const u8 *))
{
      int err;
      unsigned int avail;
      const int bs = crypto_cipher_blocksize(ctx->child);
      struct sinfo s = {
            .tfm = crypto_cipher_tfm(ctx->child),
            .fn = fn
      };
      be128 *iv;
      u8 *wsrc;
      u8 *wdst;

      err = blkcipher_walk_virt(d, w);
      if (!(avail = w->nbytes))
            return err;

      wsrc = w->src.virt.addr;
      wdst = w->dst.virt.addr;

      /* calculate first value of T */
      iv = (be128 *)w->iv;
      s.t = *iv;

      /* T <- I*Key2 */
      gf128mul_64k_bbe(&s.t, ctx->table);

      goto first;

      for (;;) {
            do {
                  /* T <- I*Key2, using the optimization
                   * discussed in the specification */
                  be128_xor(&s.t, &s.t, &ctx->mulinc[get_index128(iv)]);
                  inc(iv);

first:
                  lrw_round(&s, wdst, wsrc);

                  wsrc += bs;
                  wdst += bs;
            } while ((avail -= bs) >= bs);

            err = blkcipher_walk_done(d, w, avail);
            if (!(avail = w->nbytes))
                  break;

            wsrc = w->src.virt.addr;
            wdst = w->dst.virt.addr;
      }

      return err;
}

static int encrypt(struct blkcipher_desc *desc, struct scatterlist *dst,
               struct scatterlist *src, unsigned int nbytes)
{
      struct priv *ctx = crypto_blkcipher_ctx(desc->tfm);
      struct blkcipher_walk w;

      blkcipher_walk_init(&w, dst, src, nbytes);
      return crypt(desc, &w, ctx,
                 crypto_cipher_alg(ctx->child)->cia_encrypt);
}

static int decrypt(struct blkcipher_desc *desc, struct scatterlist *dst,
               struct scatterlist *src, unsigned int nbytes)
{
      struct priv *ctx = crypto_blkcipher_ctx(desc->tfm);
      struct blkcipher_walk w;

      blkcipher_walk_init(&w, dst, src, nbytes);
      return crypt(desc, &w, ctx,
                 crypto_cipher_alg(ctx->child)->cia_decrypt);
}

static int init_tfm(struct crypto_tfm *tfm)
{
      struct crypto_cipher *cipher;
      struct crypto_instance *inst = (void *)tfm->__crt_alg;
      struct crypto_spawn *spawn = crypto_instance_ctx(inst);
      struct priv *ctx = crypto_tfm_ctx(tfm);
      u32 *flags = &tfm->crt_flags;

      cipher = crypto_spawn_cipher(spawn);
      if (IS_ERR(cipher))
            return PTR_ERR(cipher);

      if (crypto_cipher_blocksize(cipher) != 16) {
            *flags |= CRYPTO_TFM_RES_BAD_BLOCK_LEN;
            return -EINVAL;
      }

      ctx->child = cipher;
      return 0;
}

static void exit_tfm(struct crypto_tfm *tfm)
{
      struct priv *ctx = crypto_tfm_ctx(tfm);
      if (ctx->table)
            gf128mul_free_64k(ctx->table);
      crypto_free_cipher(ctx->child);
}

static struct crypto_instance *alloc(struct rtattr **tb)
{
      struct crypto_instance *inst;
      struct crypto_alg *alg;
      int err;

      err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_BLKCIPHER);
      if (err)
            return ERR_PTR(err);

      alg = crypto_get_attr_alg(tb, CRYPTO_ALG_TYPE_CIPHER,
                          CRYPTO_ALG_TYPE_MASK);
      if (IS_ERR(alg))
            return ERR_PTR(PTR_ERR(alg));

      inst = crypto_alloc_instance("lrw", alg);
      if (IS_ERR(inst))
            goto out_put_alg;

      inst->alg.cra_flags = CRYPTO_ALG_TYPE_BLKCIPHER;
      inst->alg.cra_priority = alg->cra_priority;
      inst->alg.cra_blocksize = alg->cra_blocksize;

      if (alg->cra_alignmask < 7) inst->alg.cra_alignmask = 7;
      else inst->alg.cra_alignmask = alg->cra_alignmask;
      inst->alg.cra_type = &crypto_blkcipher_type;

      if (!(alg->cra_blocksize % 4))
            inst->alg.cra_alignmask |= 3;
      inst->alg.cra_blkcipher.ivsize = alg->cra_blocksize;
      inst->alg.cra_blkcipher.min_keysize =
            alg->cra_cipher.cia_min_keysize + alg->cra_blocksize;
      inst->alg.cra_blkcipher.max_keysize =
            alg->cra_cipher.cia_max_keysize + alg->cra_blocksize;

      inst->alg.cra_ctxsize = sizeof(struct priv);

      inst->alg.cra_init = init_tfm;
      inst->alg.cra_exit = exit_tfm;

      inst->alg.cra_blkcipher.setkey = setkey;
      inst->alg.cra_blkcipher.encrypt = encrypt;
      inst->alg.cra_blkcipher.decrypt = decrypt;

out_put_alg:
      crypto_mod_put(alg);
      return inst;
}

static void free(struct crypto_instance *inst)
{
      crypto_drop_spawn(crypto_instance_ctx(inst));
      kfree(inst);
}

static struct crypto_template crypto_tmpl = {
      .name = "lrw",
      .alloc = alloc,
      .free = free,
      .module = THIS_MODULE,
};

static int __init crypto_module_init(void)
{
      return crypto_register_template(&crypto_tmpl);
}

static void __exit crypto_module_exit(void)
{
      crypto_unregister_template(&crypto_tmpl);
}

module_init(crypto_module_init);
module_exit(crypto_module_exit);

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("LRW block cipher mode");

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