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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/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;
int err;
crypto_skcipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
crypto_skcipher_set_flags(child, crypto_skcipher_get_flags(parent) &
CRYPTO_TFM_REQ_MASK);
err = crypto_skcipher_setkey(child, key, keylen);
crypto_skcipher_set_flags(parent, crypto_skcipher_get_flags(child) &
CRYPTO_TFM_RES_MASK);
return err;
}
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[bsize * 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 && req->base.flags & CRYPTO_TFM_REQ_MAY_BACKLOG))
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;
int cbc_blocks = (nbytes + bsize - 1) / bsize - 1;
unsigned int offset;
skcipher_request_set_tfm(subreq, ctx->child);
if (cbc_blocks <= 0) {
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 = cbc_blocks * 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[bsize * 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 && req->base.flags & CRYPTO_TFM_REQ_MAY_BACKLOG))
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;
int cbc_blocks = (nbytes + bsize - 1) / bsize - 1;
unsigned int offset;
u8 *space;
skcipher_request_set_tfm(subreq, ctx->child);
if (cbc_blocks <= 0) {
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 = cbc_blocks * bsize;
rctx->offset = offset;
if (cbc_blocks <= 1)
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 crypto_attr_type *algt;
struct skcipher_alg *alg;
const char *cipher_name;
int err;
algt = crypto_get_attr_type(tb);
if (IS_ERR(algt))
return PTR_ERR(algt);
if ((algt->type ^ CRYPTO_ALG_TYPE_SKCIPHER) & algt->mask)
return -EINVAL;
cipher_name = crypto_attr_alg_name(tb[1]);
if (IS_ERR(cipher_name))
return PTR_ERR(cipher_name);
inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL);
if (!inst)
return -ENOMEM;
spawn = skcipher_instance_ctx(inst);
crypto_set_skcipher_spawn(spawn, skcipher_crypto_instance(inst));
err = crypto_grab_skcipher(spawn, cipher_name, 0,
crypto_requires_sync(algt->type,
algt->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_drop_spawn;
if (strncmp(alg->base.cra_name, "cbc(", 4))
goto err_drop_spawn;
err = crypto_inst_setname(skcipher_crypto_instance(inst), "cts",
&alg->base);
if (err)
goto err_drop_spawn;
inst->alg.base.cra_flags = alg->base.cra_flags & CRYPTO_ALG_ASYNC;
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)
goto err_drop_spawn;
out:
return err;
err_drop_spawn:
crypto_drop_skcipher(spawn);
err_free_inst:
kfree(inst);
goto out;
}
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);
}
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");