linux/crypto/xctr.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * XCTR: XOR Counter mode - Adapted from ctr.c
 *
 * (C) Copyright IBM Corp. 2007 - Joy Latten <[email protected]>
 * Copyright 2021 Google LLC
 */

/*
 * XCTR mode is a blockcipher mode of operation used to implement HCTR2. XCTR is
 * closely related to the CTR mode of operation; the main difference is that CTR
 * generates the keystream using E(CTR + IV) whereas XCTR generates the
 * keystream using E(CTR ^ IV). This allows implementations to avoid dealing
 * with multi-limb integers (as is required in CTR mode). XCTR is also specified
 * using little-endian arithmetic which makes it slightly faster on LE machines.
 *
 * See the HCTR2 paper for more details:
 *	Length-preserving encryption with HCTR2
 *      (https://eprint.iacr.org/2021/1441.pdf)
 */

#include <crypto/algapi.h>
#include <crypto/internal/cipher.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>

/* For now this implementation is limited to 16-byte blocks for simplicity */
#define XCTR_BLOCKSIZE …

static void crypto_xctr_crypt_final(struct skcipher_walk *walk,
				   struct crypto_cipher *tfm, u32 byte_ctr)
{ … }

static int crypto_xctr_crypt_segment(struct skcipher_walk *walk,
				    struct crypto_cipher *tfm, u32 byte_ctr)
{ … }

static int crypto_xctr_crypt_inplace(struct skcipher_walk *walk,
				    struct crypto_cipher *tfm, u32 byte_ctr)
{ … }

static int crypto_xctr_crypt(struct skcipher_request *req)
{ … }

static int crypto_xctr_create(struct crypto_template *tmpl, struct rtattr **tb)
{ … }

static struct crypto_template crypto_xctr_tmpl = …;

static int __init crypto_xctr_module_init(void)
{ … }

static void __exit crypto_xctr_module_exit(void)
{ … }

subsys_initcall(crypto_xctr_module_init);
module_exit(crypto_xctr_module_exit);

MODULE_LICENSE(…) …;
MODULE_DESCRIPTION(…) …;
MODULE_ALIAS_CRYPTO(…) …;
MODULE_IMPORT_NS(…);