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