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xts.c

/* XTS: as defined in IEEE1619/D16
 *    http://grouper.ieee.org/groups/1619/email/pdf00086.pdf
 *    (sector sizes which are not a multiple of 16 bytes are,
 *    however currently unsupported)
 *
 * Copyright (c) 2007 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.
 */
#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;
      struct crypto_cipher *tweak;
};

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->tweak;
      u32 *flags = &parent->crt_flags;
      int err;

      /* key consists of keys of equal size concatenated, therefore
       * the length must be even */
      if (keylen % 2) {
            /* tell the user why there was an error */
            *flags |= CRYPTO_TFM_RES_BAD_KEY_LEN;
            return -EINVAL;
      }

      /* we need two cipher instances: one to compute the inital 'tweak'
       * by encrypting the IV (usually the 'plain' iv) and the other
       * one to encrypt and decrypt the data */

      /* tweak cipher, uses Key2 i.e. the second half of *key */
      crypto_cipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
      crypto_cipher_set_flags(child, crypto_tfm_get_flags(parent) &
                               CRYPTO_TFM_REQ_MASK);
      err = crypto_cipher_setkey(child, key + keylen/2, keylen/2);
      if (err)
            return err;

      crypto_tfm_set_flags(parent, crypto_cipher_get_flags(child) &
                             CRYPTO_TFM_RES_MASK);

      child = ctx->child;

      /* data cipher, uses Key1 i.e. the first half of *key */
      crypto_cipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
      crypto_cipher_set_flags(child, crypto_tfm_get_flags(parent) &
                               CRYPTO_TFM_REQ_MASK);
      err = crypto_cipher_setkey(child, key, keylen/2);
      if (err)
            return err;

      crypto_tfm_set_flags(parent, crypto_cipher_get_flags(child) &
                             CRYPTO_TFM_RES_MASK);

      return 0;
}

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

static inline void xts_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(Key1,PP) */
      be128_xor(dst, dst, &s->t);         /* C <- T xor CC */
}

static int crypt(struct blkcipher_desc *d,
             struct blkcipher_walk *w, struct priv *ctx,
             void (*tw)(struct crypto_tfm *, u8 *, const u8 *),
             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 (!w->nbytes)
            return err;

      avail = w->nbytes;

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

      /* calculate first value of T */
      iv = (be128 *)w->iv;
      tw(crypto_cipher_tfm(ctx->tweak), (void *)&s.t, w->iv);

      goto first;

      for (;;) {
            do {
                  gf128mul_x_ble(&s.t, &s.t);

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

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

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

            avail = w->nbytes;

            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->tweak)->cia_encrypt,
                 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->tweak)->cia_encrypt,
                 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;
            crypto_free_cipher(cipher);
            return -EINVAL;
      }

      ctx->child = cipher;

      cipher = crypto_spawn_cipher(spawn);
      if (IS_ERR(cipher)) {
            crypto_free_cipher(ctx->child);
            return PTR_ERR(cipher);
      }

      /* this check isn't really needed, leave it here just in case */
      if (crypto_cipher_blocksize(cipher) != 16) {
            crypto_free_cipher(cipher);
            crypto_free_cipher(ctx->child);
            *flags |= CRYPTO_TFM_RES_BAD_BLOCK_LEN;
            return -EINVAL;
      }

      ctx->tweak = cipher;

      return 0;
}

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

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("xts", 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;

      inst->alg.cra_blkcipher.ivsize = alg->cra_blocksize;
      inst->alg.cra_blkcipher.min_keysize =
            2 * alg->cra_cipher.cia_min_keysize;
      inst->alg.cra_blkcipher.max_keysize =
            2 * alg->cra_cipher.cia_max_keysize;

      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 = "xts",
      .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("XTS block cipher mode");

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