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/*
* 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");
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