crypto/cts.c - third_party/linux - Git at Google

 /*
  * 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);
 	err = PTR_ERR(alg);
 	if (IS_ERR(alg))
 		return ERR_PTR(err);

 	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");
 MODULE_ALIAS_CRYPTO("cts");
	/*
	* 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);
	err = PTR_ERR(alg);
	if (IS_ERR(alg))
	return ERR_PTR(err);

	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");
	MODULE_ALIAS_CRYPTO("cts");