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// SPDX-License-Identifier: GPL-2.0
/*
* OFB: Output FeedBack mode
*
* Copyright (C) 2018 ARM Limited or its affiliates.
* All rights reserved.
*/
#include <crypto/algapi.h>
#include <crypto/internal/skcipher.h>
#include <linux/err.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
static int crypto_ofb_crypt(struct skcipher_request *req)
{
struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
struct crypto_cipher *cipher = skcipher_cipher_simple(tfm);
const unsigned int bsize = crypto_cipher_blocksize(cipher);
struct skcipher_walk walk;
int err;
err = skcipher_walk_virt(&walk, req, false);
while (walk.nbytes >= bsize) {
const u8 *src = walk.src.virt.addr;
u8 *dst = walk.dst.virt.addr;
u8 * const iv = walk.iv;
unsigned int nbytes = walk.nbytes;
do {
crypto_cipher_encrypt_one(cipher, iv, iv);
crypto_xor_cpy(dst, src, iv, bsize);
dst += bsize;
src += bsize;
} while ((nbytes -= bsize) >= bsize);
err = skcipher_walk_done(&walk, nbytes);
}
if (walk.nbytes) {
crypto_cipher_encrypt_one(cipher, walk.iv, walk.iv);
crypto_xor_cpy(walk.dst.virt.addr, walk.src.virt.addr, walk.iv,
walk.nbytes);
err = skcipher_walk_done(&walk, 0);
}
return err;
}
static int crypto_ofb_create(struct crypto_template *tmpl, struct rtattr **tb)
{
struct skcipher_instance *inst;
struct crypto_alg *alg;
int err;
inst = skcipher_alloc_instance_simple(tmpl, tb);
if (IS_ERR(inst))
return PTR_ERR(inst);
alg = skcipher_ialg_simple(inst);
/* OFB mode is a stream cipher. */
inst->alg.base.cra_blocksize = 1;
/*
* To simplify the implementation, configure the skcipher walk to only
* give a partial block at the very end, never earlier.
*/
inst->alg.chunksize = alg->cra_blocksize;
inst->alg.encrypt = crypto_ofb_crypt;
inst->alg.decrypt = crypto_ofb_crypt;
err = skcipher_register_instance(tmpl, inst);
if (err)
inst->free(inst);
return err;
}
static struct crypto_template crypto_ofb_tmpl = {
.name = "ofb",
.create = crypto_ofb_create,
.module = THIS_MODULE,
};
static int __init crypto_ofb_module_init(void)
{
return crypto_register_template(&crypto_ofb_tmpl);
}
static void __exit crypto_ofb_module_exit(void)
{
crypto_unregister_template(&crypto_ofb_tmpl);
}
subsys_initcall(crypto_ofb_module_init);
module_exit(crypto_ofb_module_exit);
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("OFB block cipher mode of operation");
MODULE_ALIAS_CRYPTO("ofb");
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