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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/slab.h>
#include <linux/string.h>
#include <linux/types.h>
struct crypto_cfb_ctx {
struct crypto_cipher *child;
};
static unsigned int crypto_cfb_bsize(struct crypto_skcipher *tfm)
{
struct crypto_cfb_ctx *ctx = crypto_skcipher_ctx(tfm);
struct crypto_cipher *child = ctx->child;
return crypto_cipher_blocksize(child);
}
static void crypto_cfb_encrypt_one(struct crypto_skcipher *tfm,
const u8 *src, u8 *dst)
{
struct crypto_cfb_ctx *ctx = crypto_skcipher_ctx(tfm);
crypto_cipher_encrypt_one(ctx->child, 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);
memcpy(iv, dst, bsize);
src += bsize;
dst += bsize;
} while ((nbytes -= bsize) >= 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, iv, 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 *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);
memcpy(walk->iv, iv, 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_setkey(struct crypto_skcipher *parent, const u8 *key,
unsigned int keylen)
{
struct crypto_cfb_ctx *ctx = crypto_skcipher_ctx(parent);
struct crypto_cipher *child = ctx->child;
int err;
crypto_cipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
crypto_cipher_set_flags(child, crypto_skcipher_get_flags(parent) &
CRYPTO_TFM_REQ_MASK);
err = crypto_cipher_setkey(child, key, keylen);
crypto_skcipher_set_flags(parent, crypto_cipher_get_flags(child) &
CRYPTO_TFM_RES_MASK);
return err;
}
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_init_tfm(struct crypto_skcipher *tfm)
{
struct skcipher_instance *inst = skcipher_alg_instance(tfm);
struct crypto_spawn *spawn = skcipher_instance_ctx(inst);
struct crypto_cfb_ctx *ctx = crypto_skcipher_ctx(tfm);
struct crypto_cipher *cipher;
cipher = crypto_spawn_cipher(spawn);
if (IS_ERR(cipher))
return PTR_ERR(cipher);
ctx->child = cipher;
return 0;
}
static void crypto_cfb_exit_tfm(struct crypto_skcipher *tfm)
{
struct crypto_cfb_ctx *ctx = crypto_skcipher_ctx(tfm);
crypto_free_cipher(ctx->child);
}
static void crypto_cfb_free(struct skcipher_instance *inst)
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