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//SPDX-License-Identifier: GPL-2.0
/*
* CFB: Cipher FeedBack mode
*
* Copyright (c) 2018 James.Bottomley@HansenPartnership.com
*
* CFB is a stream cipher mode which is layered on to a block
* encryption scheme. It works very much like a one time pad where
* the pad is generated initially from the encrypted IV and then
* subsequently from the encrypted previous block of ciphertext. The
* pad is XOR'd into the plain text to get the final ciphertext.
*
* The scheme of CFB is best described by wikipedia:
*
* https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#CFB
*
* Note that since the pad for both encryption and decryption is
* generated by an encryption operation, CFB never uses the block
* decryption function.
*/
#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>
#include <linux/string.h>
static unsigned int crypto_cfb_bsize(struct crypto_skcipher *tfm)
{
return crypto_cipher_blocksize(skcipher_cipher_simple(tfm));
}
static void crypto_cfb_encrypt_one(struct crypto_skcipher *tfm,
const u8 *src, u8 *dst)
{
crypto_cipher_encrypt_one(skcipher_cipher_simple(tfm), dst, src);
}
/* final encrypt and decrypt is the same */
static void crypto_cfb_final(struct skcipher_walk *walk,
struct crypto_skcipher *tfm)
{
const unsigned long alignmask = crypto_skcipher_alignmask(tfm);
u8 tmp[MAX_CIPHER_BLOCKSIZE + MAX_CIPHER_ALIGNMASK];
u8 *stream = PTR_ALIGN(tmp + 0, alignmask + 1);
u8 *src = walk->src.virt.addr;
u8 *dst = walk->dst.virt.addr;
u8 *iv = walk->iv;
unsigned int nbytes = walk->nbytes;
crypto_cfb_encrypt_one(tfm, iv, stream);
crypto_xor_cpy(dst, stream, src, nbytes);
}
static int crypto_cfb_encrypt_segment(struct skcipher_walk *walk,
struct crypto_skcipher *tfm)
{
const unsigned int bsize = crypto_cfb_bsize(tfm);
unsigned int nbytes = walk->nbytes;
u8 *src = walk->src.virt.addr;
u8 *dst = walk->dst.virt.addr;
u8 *iv = walk->iv;
do {
crypto_cfb_encrypt_one(tfm, iv, dst);
crypto_xor(dst, src, bsize);
iv = dst;
src += bsize;
dst += bsize;
} while ((nbytes -= bsize) >= bsize);
memcpy(walk->iv, iv, bsize);
return nbytes;
}
static int crypto_cfb_encrypt_inplace(struct skcipher_walk *walk,
struct crypto_skcipher *tfm)
{
const unsigned int bsize = crypto_cfb_bsize(tfm);
unsigned int nbytes = walk->nbytes;
u8 *src = walk->src.virt.addr;
u8 *iv = walk->iv;
u8 tmp[MAX_CIPHER_BLOCKSIZE];
do {
crypto_cfb_encrypt_one(tfm, iv, tmp);
crypto_xor(src, tmp, bsize);
iv = src;
src += bsize;
} while ((nbytes -= bsize) >= bsize);
memcpy(walk->iv, iv, bsize);
return nbytes;
}
static int crypto_cfb_encrypt(struct skcipher_request *req)
{
struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
struct skcipher_walk walk;
unsigned int bsize = crypto_cfb_bsize(tfm);
int err;
err = skcipher_walk_virt(&walk, req, false);
while (walk.nbytes >= bsize) {
if (walk.src.virt.addr == walk.dst.virt.addr)
err = crypto_cfb_encrypt_inplace(&walk, tfm);
else
err = crypto_cfb_encrypt_segment(&walk, tfm);
err = skcipher_walk_done(&walk, err);
}
if (walk.nbytes) {
crypto_cfb_final(&walk, tfm);
err = skcipher_walk_done(&walk, 0);
}
return err;
}
static int crypto_cfb_decrypt_segment(struct skcipher_walk *walk,
struct crypto_skcipher *tfm)
{
const unsigned int bsize = crypto_cfb_bsize(tfm);
unsigned int nbytes = walk->nbytes;
u8 *src = walk->src.virt.addr;
u8 *dst = walk->dst.virt.addr;
u8 *iv = walk->iv;
do {
crypto_cfb_encrypt_one(tfm, iv, dst);
crypto_xor(dst, src, bsize);
iv = src;
src += bsize;
dst += bsize;
} while ((nbytes -= bsize) >= bsize);
memcpy(walk->iv, iv, bsize);
return nbytes;
}
static int crypto_cfb_decrypt_inplace(struct skcipher_walk *walk,
struct crypto_skcipher *tfm)
{
const unsigned int bsize = crypto_cfb_bsize(tfm);
unsigned int nbytes = walk->nbytes;
u8 *src = walk->src.virt.addr;
u8 * const iv = walk->iv;
u8 tmp[MAX_CIPHER_BLOCKSIZE];
do {
crypto_cfb_encrypt_one(tfm, iv, tmp);
memcpy(iv, src, bsize);
crypto_xor(src, tmp, bsize);
src += bsize;
} while ((nbytes -= bsize) >= bsize);
return nbytes;
}
static int crypto_cfb_decrypt_blocks(struct skcipher_walk *walk,
struct crypto_skcipher *tfm)
{
if (walk->src.virt.addr == walk->dst.virt.addr)
return crypto_cfb_decrypt_inplace(walk, tfm);
else
return crypto_cfb_decrypt_segment(walk, tfm);
}
static int crypto_cfb_decrypt(struct skcipher_request *req)
{
struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
struct skcipher_walk walk;
const unsigned int bsize = crypto_cfb_bsize(tfm);
int err;
err = skcipher_walk_virt(&walk, req, false);
while (walk.nbytes >= bsize) {
err = crypto_cfb_decrypt_blocks(&walk, tfm);
err = skcipher_walk_done(&walk, err);
}
if (walk.nbytes) {
crypto_cfb_final(&walk, tfm);
err = skcipher_walk_done(&walk, 0);
}
return err;
}
static int crypto_cfb_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);
/* CFB 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_cfb_encrypt;
inst->alg.decrypt = crypto_cfb_decrypt;
err = skcipher_register_instance(tmpl, inst);
if (err)
inst->free(inst);
return err;
}
static struct crypto_template crypto_cfb_tmpl = {
.name = "cfb",
.create = crypto_cfb_create,
.module = THIS_MODULE,
};
static int __init crypto_cfb_module_init(void)
{
return crypto_register_template(&crypto_cfb_tmpl);
}
static void __exit crypto_cfb_module_exit(void)
{
crypto_unregister_template(&crypto_cfb_tmpl);
}
subsys_initcall(crypto_cfb_module_init);
module_exit(crypto_cfb_module_exit);
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("CFB block cipher mode of operation");
MODULE_ALIAS_CRYPTO("cfb");
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