/*
 * 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 */
	memzero_explicit(iv, 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 *