/*
   * 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 <crypto/internal/skcipher.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>

  #include <linux/compiler.h>

  
  struct crypto_cts_ctx {

  	struct crypto_skcipher *child;

  };

  struct crypto_cts_reqctx {
  	struct scatterlist sg[2];
  	unsigned offset;
  	struct skcipher_request subreq;
  };
  
  static inline u8 *crypto_cts_reqctx_space(struct skcipher_request *req)

  {

  	struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
  	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
  	struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
  	struct crypto_skcipher *child = ctx->child;

  	return PTR_ALIGN((u8 *)(rctx + 1) + crypto_skcipher_reqsize(child),
  			 crypto_skcipher_alignmask(tfm) + 1);

  }

  static int crypto_cts_setkey(struct crypto_skcipher *parent, const u8 *key,
  			     unsigned int keylen)

  {

  	struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(parent);
  	struct crypto_skcipher *child = ctx->child;

  	crypto_skcipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
  	crypto_skcipher_set_flags(child, crypto_skcipher_get_flags(parent) &
  					 CRYPTO_TFM_REQ_MASK);

  	return crypto_skcipher_setkey(child, key, keylen);

  }

  static void cts_cbc_crypt_done(struct crypto_async_request *areq, int err)
  {
  	struct skcipher_request *req = areq->data;

  	if (err == -EINPROGRESS)
  		return;

  	skcipher_request_complete(req, err);
  }

  static int cts_cbc_encrypt(struct skcipher_request *req)
  {
  	struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
  	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
  	struct skcipher_request *subreq = &rctx->subreq;
  	int bsize = crypto_skcipher_blocksize(tfm);

  	u8 d[MAX_CIPHER_BLOCKSIZE * 2] __aligned(__alignof__(u32));

  	struct scatterlist *sg;
  	unsigned int offset;
  	int lastn;
  
  	offset = rctx->offset;
  	lastn = req->cryptlen - offset;
  
  	sg = scatterwalk_ffwd(rctx->sg, req->dst, offset - bsize);
  	scatterwalk_map_and_copy(d + bsize, sg, 0, bsize, 0);
  
  	memset(d, 0, bsize);
  	scatterwalk_map_and_copy(d, req->src, offset, lastn, 0);
  
  	scatterwalk_map_and_copy(d, sg, 0, bsize + lastn, 1);
  	memzero_explicit(d, sizeof(d));
  
  	skcipher_request_set_callback(subreq, req->base.flags &
  					      CRYPTO_TFM_REQ_MAY_BACKLOG,
  				      cts_cbc_crypt_done, req);
  	skcipher_request_set_crypt(subreq, sg, sg, bsize, req->iv);
  	return crypto_skcipher_encrypt(subreq);
  }

  static void crypto_cts_encrypt_done(struct crypto_async_request *areq, int err)
  {
  	struct skcipher_request *req = areq->data;

  	if (err)
  		goto out;

  	err = cts_cbc_encrypt(req);

  	if (err == -EINPROGRESS || err == -EBUSY)

  		return;

  out:
  	skcipher_request_complete(req, err);
  }

  static int crypto_cts_encrypt(struct skcipher_request *req)
  {
  	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
  	struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
  	struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
  	struct skcipher_request *subreq = &rctx->subreq;
  	int bsize = crypto_skcipher_blocksize(tfm);
  	unsigned int nbytes = req->cryptlen;

  	unsigned int offset;
  
  	skcipher_request_set_tfm(subreq, ctx->child);

  	if (nbytes < bsize)
  		return -EINVAL;
  
  	if (nbytes == bsize) {

  		skcipher_request_set_callback(subreq, req->base.flags,
  					      req->base.complete,
  					      req->base.data);
  		skcipher_request_set_crypt(subreq, req->src, req->dst, nbytes,
  					   req->iv);
  		return crypto_skcipher_encrypt(subreq);
  	}

  	offset = rounddown(nbytes - 1, bsize);

  	rctx->offset = offset;

  	skcipher_request_set_callback(subreq, req->base.flags,
  				      crypto_cts_encrypt_done, req);
  	skcipher_request_set_crypt(subreq, req->src, req->dst,
  				   offset, req->iv);

  	return crypto_skcipher_encrypt(subreq) ?:
  	       cts_cbc_encrypt(req);

  }

  static int cts_cbc_decrypt(struct skcipher_request *req)

  {

  	struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
  	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
  	struct skcipher_request *subreq = &rctx->subreq;
  	int bsize = crypto_skcipher_blocksize(tfm);

  	u8 d[MAX_CIPHER_BLOCKSIZE * 2] __aligned(__alignof__(u32));

  	struct scatterlist *sg;
  	unsigned int offset;
  	u8 *space;
  	int lastn;
  
  	offset = rctx->offset;
  	lastn = req->cryptlen - offset;
  
  	sg = scatterwalk_ffwd(rctx->sg, req->dst, offset - bsize);
  
  	/* 1. Decrypt Cn-1 (s) to create Dn */
  	scatterwalk_map_and_copy(d + bsize, sg, 0, bsize, 0);
  	space = crypto_cts_reqctx_space(req);
  	crypto_xor(d + bsize, space, bsize);
  	/* 2. Pad Cn with zeros at the end to create C of length BB */
  	memset(d, 0, bsize);
  	scatterwalk_map_and_copy(d, req->src, offset, lastn, 0);
  	/* 3. Exclusive-or Dn with C to create Xn */
  	/* 4. Select the first Ln bytes of Xn to create Pn */
  	crypto_xor(d + bsize, d, lastn);
  
  	/* 5. Append the tail (BB - Ln) bytes of Xn to Cn to create En */
  	memcpy(d + lastn, d + bsize + lastn, bsize - lastn);
  	/* 6. Decrypt En to create Pn-1 */

  	scatterwalk_map_and_copy(d, sg, 0, bsize + lastn, 1);
  	memzero_explicit(d, sizeof(d));

  	skcipher_request_set_callback(subreq, req->base.flags &
  					      CRYPTO_TFM_REQ_MAY_BACKLOG,
  				      cts_cbc_crypt_done, req);
  
  	skcipher_request_set_crypt(subreq, sg, sg, bsize, space);
  	return crypto_skcipher_decrypt(subreq);

  }

  static void crypto_cts_decrypt_done(struct crypto_async_request *areq, int err)

  {

  	struct skcipher_request *req = areq->data;

  	if (err)
  		goto out;

  	err = cts_cbc_decrypt(req);

  	if (err == -EINPROGRESS || err == -EBUSY)

  		return;

  out:
  	skcipher_request_complete(req, err);
  }

  static int crypto_cts_decrypt(struct skcipher_request *req)
  {
  	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
  	struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
  	struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
  	struct skcipher_request *subreq = &rctx->subreq;
  	int bsize = crypto_skcipher_blocksize(tfm);
  	unsigned int nbytes = req->cryptlen;

  	unsigned int offset;
  	u8 *space;
  
  	skcipher_request_set_tfm(subreq, ctx->child);

  	if (nbytes < bsize)
  		return -EINVAL;
  
  	if (nbytes == bsize) {

  		skcipher_request_set_callback(subreq, req->base.flags,
  					      req->base.complete,
  					      req->base.data);
  		skcipher_request_set_crypt(subreq, req->src, req->dst, nbytes,
  					   req->iv);
  		return crypto_skcipher_decrypt(subreq);
  	}

  	skcipher_request_set_callback(subreq, req->base.flags,
  				      crypto_cts_decrypt_done, req);

  	space = crypto_cts_reqctx_space(req);

  	offset = rounddown(nbytes - 1, bsize);

  	rctx->offset = offset;

  	if (offset <= bsize)

  		memcpy(space, req->iv, bsize);
  	else
  		scatterwalk_map_and_copy(space, req->src, offset - 2 * bsize,
  					 bsize, 0);

  	skcipher_request_set_crypt(subreq, req->src, req->dst,
  				   offset, req->iv);

  	return crypto_skcipher_decrypt(subreq) ?:
  	       cts_cbc_decrypt(req);

  }

  static int crypto_cts_init_tfm(struct crypto_skcipher *tfm)

  {

  	struct skcipher_instance *inst = skcipher_alg_instance(tfm);
  	struct crypto_skcipher_spawn *spawn = skcipher_instance_ctx(inst);
  	struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
  	struct crypto_skcipher *cipher;
  	unsigned reqsize;
  	unsigned bsize;
  	unsigned align;

  	cipher = crypto_spawn_skcipher(spawn);

  	if (IS_ERR(cipher))
  		return PTR_ERR(cipher);
  
  	ctx->child = cipher;

  
  	align = crypto_skcipher_alignmask(tfm);
  	bsize = crypto_skcipher_blocksize(cipher);
  	reqsize = ALIGN(sizeof(struct crypto_cts_reqctx) +
  			crypto_skcipher_reqsize(cipher),
  			crypto_tfm_ctx_alignment()) +
  		  (align & ~(crypto_tfm_ctx_alignment() - 1)) + bsize;
  
  	crypto_skcipher_set_reqsize(tfm, reqsize);

  	return 0;
  }

  static void crypto_cts_exit_tfm(struct crypto_skcipher *tfm)

  {

  	struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
  
  	crypto_free_skcipher(ctx->child);

  }

  static void crypto_cts_free(struct skcipher_instance *inst)

  {

  	crypto_drop_skcipher(skcipher_instance_ctx(inst));
  	kfree(inst);
  }
  
  static int crypto_cts_create(struct crypto_template *tmpl, struct rtattr **tb)
  {
  	struct crypto_skcipher_spawn *spawn;
  	struct skcipher_instance *inst;

  	struct skcipher_alg *alg;

  	u32 mask;

  	int err;

  	err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_SKCIPHER, &mask);
  	if (err)
  		return err;

  	inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL);
  	if (!inst)
  		return -ENOMEM;
  
  	spawn = skcipher_instance_ctx(inst);

  	err = crypto_grab_skcipher(spawn, skcipher_crypto_instance(inst),

  				   crypto_attr_alg_name(tb[1]), 0, mask);

  	if (err)

  		goto err_free_inst;

  	alg = crypto_spawn_skcipher_alg(spawn);

  	err = -EINVAL;
  	if (crypto_skcipher_alg_ivsize(alg) != alg->base.cra_blocksize)

  		goto err_free_inst;

  	if (strncmp(alg->base.cra_name, "cbc(", 4))

  		goto err_free_inst;

  	err = crypto_inst_setname(skcipher_crypto_instance(inst), "cts",
  				  &alg->base);
  	if (err)

  		goto err_free_inst;

  	inst->alg.base.cra_priority = alg->base.cra_priority;
  	inst->alg.base.cra_blocksize = alg->base.cra_blocksize;
  	inst->alg.base.cra_alignmask = alg->base.cra_alignmask;

  	inst->alg.ivsize = alg->base.cra_blocksize;
  	inst->alg.chunksize = crypto_skcipher_alg_chunksize(alg);
  	inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(alg);
  	inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(alg);

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

  	inst->alg.init = crypto_cts_init_tfm;
  	inst->alg.exit = crypto_cts_exit_tfm;

  	inst->alg.setkey = crypto_cts_setkey;
  	inst->alg.encrypt = crypto_cts_encrypt;
  	inst->alg.decrypt = crypto_cts_decrypt;

  	inst->free = crypto_cts_free;

  	err = skcipher_register_instance(tmpl, inst);

  	if (err) {

  err_free_inst:

  		crypto_cts_free(inst);
  	}
  	return err;

  }
  
  static struct crypto_template crypto_cts_tmpl = {
  	.name = "cts",

  	.create = crypto_cts_create,

  	.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);
  }

  subsys_initcall(crypto_cts_module_init);

  module_exit(crypto_cts_module_exit);
  
  MODULE_LICENSE("Dual BSD/GPL");
  MODULE_DESCRIPTION("CTS-CBC CipherText Stealing for CBC");

  MODULE_ALIAS_CRYPTO("cts");