/*
   * CTS: Cipher Text Stealing mode
   *
   * COPYRIGHT (c) 2008
   * The Regents of the University of Michigan
   * ALL RIGHTS RESERVED
   *
   * Permission is granted to use, copy, create derivative works
   * and redistribute this software and such derivative works
   * for any purpose, so long as the name of The University of
   * Michigan is not used in any advertising or publicity
   * pertaining to the use of distribution of this software
   * without specific, written prior authorization.  If the
   * above copyright notice or any other identification of the
   * University of Michigan is included in any copy of any
   * portion of this software, then the disclaimer below must
   * also be included.
   *
   * THIS SOFTWARE IS PROVIDED AS IS, WITHOUT REPRESENTATION
   * FROM THE UNIVERSITY OF MICHIGAN AS TO ITS FITNESS FOR ANY
   * PURPOSE, AND WITHOUT WARRANTY BY THE UNIVERSITY OF
   * MICHIGAN OF ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING
   * WITHOUT LIMITATION THE IMPLIED WARRANTIES OF
   * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE
   * REGENTS OF THE UNIVERSITY OF MICHIGAN SHALL NOT BE LIABLE
   * FOR ANY DAMAGES, INCLUDING SPECIAL, INDIRECT, INCIDENTAL, OR
   * CONSEQUENTIAL DAMAGES, WITH RESPECT TO ANY CLAIM ARISING
   * OUT OF OR IN CONNECTION WITH THE USE OF THE SOFTWARE, EVEN
   * IF IT HAS BEEN OR IS HEREAFTER ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGES.
   */
  
  /* Derived from various:
   *	Copyright (c) 2006 Herbert Xu <herbert@gondor.apana.org.au>
   */
  
  /*
   * This is the Cipher Text Stealing mode as described by
   * Section 8 of rfc2040 and referenced by rfc3962.
   * rfc3962 includes errata information in its Appendix A.
   */
  
  #include <crypto/algapi.h>
  #include <linux/err.h>
  #include <linux/init.h>
  #include <linux/kernel.h>
  #include <linux/log2.h>
  #include <linux/module.h>
  #include <linux/scatterlist.h>
  #include <crypto/scatterwalk.h>
  #include <linux/slab.h>
  
  struct crypto_cts_ctx {
  	struct crypto_blkcipher *child;
  };
  
  static int crypto_cts_setkey(struct crypto_tfm *parent, const u8 *key,
  			     unsigned int keylen)
  {
  	struct crypto_cts_ctx *ctx = crypto_tfm_ctx(parent);
  	struct crypto_blkcipher *child = ctx->child;
  	int err;
  
  	crypto_blkcipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
  	crypto_blkcipher_set_flags(child, crypto_tfm_get_flags(parent) &
  				       CRYPTO_TFM_REQ_MASK);
  	err = crypto_blkcipher_setkey(child, key, keylen);
  	crypto_tfm_set_flags(parent, crypto_blkcipher_get_flags(child) &
  				     CRYPTO_TFM_RES_MASK);
  	return err;
  }
  
  static int cts_cbc_encrypt(struct crypto_cts_ctx *ctx,
  			   struct blkcipher_desc *desc,
  			   struct scatterlist *dst,
  			   struct scatterlist *src,
  			   unsigned int offset,
  			   unsigned int nbytes)
  {
  	int bsize = crypto_blkcipher_blocksize(desc->tfm);
  	u8 tmp[bsize], tmp2[bsize];
  	struct blkcipher_desc lcldesc;
  	struct scatterlist sgsrc[1], sgdst[1];
  	int lastn = nbytes - bsize;
  	u8 iv[bsize];
  	u8 s[bsize * 2], d[bsize * 2];
  	int err;
  
  	if (lastn < 0)
  		return -EINVAL;
  
  	sg_init_table(sgsrc, 1);
  	sg_init_table(sgdst, 1);
  
  	memset(s, 0, sizeof(s));
  	scatterwalk_map_and_copy(s, src, offset, nbytes, 0);
  
  	memcpy(iv, desc->info, bsize);
  
  	lcldesc.tfm = ctx->child;
  	lcldesc.info = iv;
  	lcldesc.flags = desc->flags;
  
  	sg_set_buf(&sgsrc[0], s, bsize);
  	sg_set_buf(&sgdst[0], tmp, bsize);
  	err = crypto_blkcipher_encrypt_iv(&lcldesc, sgdst, sgsrc, bsize);
  
  	memcpy(d + bsize, tmp, lastn);
  
  	lcldesc.info = tmp;
  
  	sg_set_buf(&sgsrc[0], s + bsize, bsize);
  	sg_set_buf(&sgdst[0], tmp2, bsize);
  	err = crypto_blkcipher_encrypt_iv(&lcldesc, sgdst, sgsrc, bsize);
  
  	memcpy(d, tmp2, bsize);
  
  	scatterwalk_map_and_copy(d, dst, offset, nbytes, 1);
  
  	memcpy(desc->info, tmp2, bsize);
  
  	return err;
  }
  
  static int crypto_cts_encrypt(struct blkcipher_desc *desc,
  			      struct scatterlist *dst, struct scatterlist *src,
  			      unsigned int nbytes)
  {
  	struct crypto_cts_ctx *ctx = crypto_blkcipher_ctx(desc->tfm);
  	int bsize = crypto_blkcipher_blocksize(desc->tfm);
  	int tot_blocks = (nbytes + bsize - 1) / bsize;
  	int cbc_blocks = tot_blocks > 2 ? tot_blocks - 2 : 0;
  	struct blkcipher_desc lcldesc;
  	int err;
  
  	lcldesc.tfm = ctx->child;
  	lcldesc.info = desc->info;
  	lcldesc.flags = desc->flags;
  
  	if (tot_blocks == 1) {
  		err = crypto_blkcipher_encrypt_iv(&lcldesc, dst, src, bsize);
  	} else if (nbytes <= bsize * 2) {
  		err = cts_cbc_encrypt(ctx, desc, dst, src, 0, nbytes);
  	} else {
  		/* do normal function for tot_blocks - 2 */
  		err = crypto_blkcipher_encrypt_iv(&lcldesc, dst, src,
  							cbc_blocks * bsize);
  		if (err == 0) {
  			/* do cts for final two blocks */
  			err = cts_cbc_encrypt(ctx, desc, dst, src,
  						cbc_blocks * bsize,
  						nbytes - (cbc_blocks * bsize));
  		}
  	}
  
  	return err;
  }
  
  static int cts_cbc_decrypt(struct crypto_cts_ctx *ctx,
  			   struct blkcipher_desc *desc,
  			   struct scatterlist *dst,
  			   struct scatterlist *src,
  			   unsigned int offset,
  			   unsigned int nbytes)
  {
  	int bsize = crypto_blkcipher_blocksize(desc->tfm);
  	u8 tmp[bsize];
  	struct blkcipher_desc lcldesc;
  	struct scatterlist sgsrc[1], sgdst[1];
  	int lastn = nbytes - bsize;
  	u8 iv[bsize];
  	u8 s[bsize * 2], d[bsize * 2];
  	int err;
  
  	if (lastn < 0)
  		return -EINVAL;
  
  	sg_init_table(sgsrc, 1);
  	sg_init_table(sgdst, 1);
  
  	scatterwalk_map_and_copy(s, src, offset, nbytes, 0);
  
  	lcldesc.tfm = ctx->child;
  	lcldesc.info = iv;
  	lcldesc.flags = desc->flags;
  
  	/* 1. Decrypt Cn-1 (s) to create Dn (tmp)*/
  	memset(iv, 0, sizeof(iv));
  	sg_set_buf(&sgsrc[0], s, bsize);
  	sg_set_buf(&sgdst[0], tmp, bsize);
  	err = crypto_blkcipher_decrypt_iv(&lcldesc, sgdst, sgsrc, bsize);
  	if (err)
  		return err;
  	/* 2. Pad Cn with zeros at the end to create C of length BB */
  	memset(iv, 0, sizeof(iv));
  	memcpy(iv, s + bsize, lastn);
  	/* 3. Exclusive-or Dn (tmp) with C (iv) to create Xn (tmp) */
  	crypto_xor(tmp, iv, bsize);
  	/* 4. Select the first Ln bytes of Xn (tmp) to create Pn */
  	memcpy(d + bsize, tmp, lastn);
  
  	/* 5. Append the tail (BB - Ln) bytes of Xn (tmp) to Cn to create En */
  	memcpy(s + bsize + lastn, tmp + lastn, bsize - lastn);
  	/* 6. Decrypt En to create Pn-1 */
  	memset(iv, 0, sizeof(iv));
  	sg_set_buf(&sgsrc[0], s + bsize, bsize);
  	sg_set_buf(&sgdst[0], d, bsize);
  	err = crypto_blkcipher_decrypt_iv(&lcldesc, sgdst, sgsrc, bsize);
  
  	/* XOR with previous block */
  	crypto_xor(d, desc->info, bsize);
  
  	scatterwalk_map_and_copy(d, dst, offset, nbytes, 1);
  
  	memcpy(desc->info, s, bsize);
  	return err;
  }
  
  static int crypto_cts_decrypt(struct blkcipher_desc *desc,
  			      struct scatterlist *dst, struct scatterlist *src,
  			      unsigned int nbytes)
  {
  	struct crypto_cts_ctx *ctx = crypto_blkcipher_ctx(desc->tfm);
  	int bsize = crypto_blkcipher_blocksize(desc->tfm);
  	int tot_blocks = (nbytes + bsize - 1) / bsize;
  	int cbc_blocks = tot_blocks > 2 ? tot_blocks - 2 : 0;
  	struct blkcipher_desc lcldesc;
  	int err;
  
  	lcldesc.tfm = ctx->child;
  	lcldesc.info = desc->info;
  	lcldesc.flags = desc->flags;
  
  	if (tot_blocks == 1) {
  		err = crypto_blkcipher_decrypt_iv(&lcldesc, dst, src, bsize);
  	} else if (nbytes <= bsize * 2) {
  		err = cts_cbc_decrypt(ctx, desc, dst, src, 0, nbytes);
  	} else {
  		/* do normal function for tot_blocks - 2 */
  		err = crypto_blkcipher_decrypt_iv(&lcldesc, dst, src,
  							cbc_blocks * bsize);
  		if (err == 0) {
  			/* do cts for final two blocks */
  			err = cts_cbc_decrypt(ctx, desc, dst, src,
  						cbc_blocks * bsize,
  						nbytes - (cbc_blocks * bsize));
  		}
  	}
  	return err;
  }
  
  static int crypto_cts_init_tfm(struct crypto_tfm *tfm)
  {
  	struct crypto_instance *inst = (void *)tfm->__crt_alg;
  	struct crypto_spawn *spawn = crypto_instance_ctx(inst);
  	struct crypto_cts_ctx *ctx = crypto_tfm_ctx(tfm);
  	struct crypto_blkcipher *cipher;
  
  	cipher = crypto_spawn_blkcipher(spawn);
  	if (IS_ERR(cipher))
  		return PTR_ERR(cipher);
  
  	ctx->child = cipher;
  	return 0;
  }
  
  static void crypto_cts_exit_tfm(struct crypto_tfm *tfm)
  {
  	struct crypto_cts_ctx *ctx = crypto_tfm_ctx(tfm);
  	crypto_free_blkcipher(ctx->child);
  }
  
  static struct crypto_instance *crypto_cts_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_attr_alg(tb[1], CRYPTO_ALG_TYPE_BLKCIPHER,
  				  CRYPTO_ALG_TYPE_MASK);
  	if (IS_ERR(alg))
  		return ERR_CAST(alg);
  
  	inst = ERR_PTR(-EINVAL);
  	if (!is_power_of_2(alg->cra_blocksize))
  		goto out_put_alg;
  
  	inst = crypto_alloc_instance("cts", 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;
  	inst->alg.cra_alignmask = alg->cra_alignmask;
  	inst->alg.cra_type = &crypto_blkcipher_type;
  
  	/* We access the data as u32s when xoring. */
  	inst->alg.cra_alignmask |= __alignof__(u32) - 1;
  
  	inst->alg.cra_blkcipher.ivsize = alg->cra_blocksize;
  	inst->alg.cra_blkcipher.min_keysize = alg->cra_blkcipher.min_keysize;
  	inst->alg.cra_blkcipher.max_keysize = alg->cra_blkcipher.max_keysize;
  
  	inst->alg.cra_blkcipher.geniv = "seqiv";
  
  	inst->alg.cra_ctxsize = sizeof(struct crypto_cts_ctx);
  
  	inst->alg.cra_init = crypto_cts_init_tfm;
  	inst->alg.cra_exit = crypto_cts_exit_tfm;
  
  	inst->alg.cra_blkcipher.setkey = crypto_cts_setkey;
  	inst->alg.cra_blkcipher.encrypt = crypto_cts_encrypt;
  	inst->alg.cra_blkcipher.decrypt = crypto_cts_decrypt;
  
  out_put_alg:
  	crypto_mod_put(alg);
  	return inst;
  }
  
  static void crypto_cts_free(struct crypto_instance *inst)
  {
  	crypto_drop_spawn(crypto_instance_ctx(inst));
  	kfree(inst);
  }
  
  static struct crypto_template crypto_cts_tmpl = {
  	.name = "cts",
  	.alloc = crypto_cts_alloc,
  	.free = crypto_cts_free,
  	.module = THIS_MODULE,
  };
  
  static int __init crypto_cts_module_init(void)
  {
  	return crypto_register_template(&crypto_cts_tmpl);
  }
  
  static void __exit crypto_cts_module_exit(void)
  {
  	crypto_unregister_template(&crypto_cts_tmpl);
  }
  
  module_init(crypto_cts_module_init);
  module_exit(crypto_cts_module_exit);
  
  MODULE_LICENSE("Dual BSD/GPL");
  MODULE_DESCRIPTION("CTS-CBC CipherText Stealing for CBC");