/* 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 initial '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
  	};

  	u8 *wsrc;
  	u8 *wdst;
  
  	err = blkcipher_walk_virt(d, w);
  	if (!w->nbytes)
  		return err;

  	s.t = (be128 *)w->iv;

  	avail = w->nbytes;
  
  	wsrc = w->src.virt.addr;
  	wdst = w->dst.virt.addr;
  
  	/* calculate first value of T */

  	tw(crypto_cipher_tfm(ctx->tweak), w->iv, 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_CAST(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");