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1// SPDX-License-Identifier: GPL-2.0-or-later2/*3 * XCTR: XOR Counter mode - Adapted from ctr.c4 *5 * (C) Copyright IBM Corp. 2007 - Joy Latten <latten@us.ibm.com>6 * Copyright 2021 Google LLC7 */8 9/*10 * XCTR mode is a blockcipher mode of operation used to implement HCTR2. XCTR is11 * closely related to the CTR mode of operation; the main difference is that CTR12 * generates the keystream using E(CTR + IV) whereas XCTR generates the13 * keystream using E(CTR ^ IV). This allows implementations to avoid dealing14 * with multi-limb integers (as is required in CTR mode). XCTR is also specified15 * using little-endian arithmetic which makes it slightly faster on LE machines.16 *17 * See the HCTR2 paper for more details:18 * Length-preserving encryption with HCTR219 * (https://eprint.iacr.org/2021/1441.pdf)20 */21 22#include <crypto/algapi.h>23#include <crypto/internal/cipher.h>24#include <crypto/internal/skcipher.h>25#include <linux/err.h>26#include <linux/init.h>27#include <linux/kernel.h>28#include <linux/module.h>29#include <linux/slab.h>30 31/* For now this implementation is limited to 16-byte blocks for simplicity */32#define XCTR_BLOCKSIZE 1633 34static void crypto_xctr_crypt_final(struct skcipher_walk *walk,35 struct crypto_cipher *tfm, u32 byte_ctr)36{37 u8 keystream[XCTR_BLOCKSIZE];38 const u8 *src = walk->src.virt.addr;39 u8 *dst = walk->dst.virt.addr;40 unsigned int nbytes = walk->nbytes;41 __le32 ctr32 = cpu_to_le32(byte_ctr / XCTR_BLOCKSIZE + 1);42 43 crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));44 crypto_cipher_encrypt_one(tfm, keystream, walk->iv);45 crypto_xor_cpy(dst, keystream, src, nbytes);46 crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));47}48 49static int crypto_xctr_crypt_segment(struct skcipher_walk *walk,50 struct crypto_cipher *tfm, u32 byte_ctr)51{52 void (*fn)(struct crypto_tfm *, u8 *, const u8 *) =53 crypto_cipher_alg(tfm)->cia_encrypt;54 const u8 *src = walk->src.virt.addr;55 u8 *dst = walk->dst.virt.addr;56 unsigned int nbytes = walk->nbytes;57 __le32 ctr32 = cpu_to_le32(byte_ctr / XCTR_BLOCKSIZE + 1);58 59 do {60 crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));61 fn(crypto_cipher_tfm(tfm), dst, walk->iv);62 crypto_xor(dst, src, XCTR_BLOCKSIZE);63 crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));64 65 le32_add_cpu(&ctr32, 1);66 67 src += XCTR_BLOCKSIZE;68 dst += XCTR_BLOCKSIZE;69 } while ((nbytes -= XCTR_BLOCKSIZE) >= XCTR_BLOCKSIZE);70 71 return nbytes;72}73 74static int crypto_xctr_crypt_inplace(struct skcipher_walk *walk,75 struct crypto_cipher *tfm, u32 byte_ctr)76{77 void (*fn)(struct crypto_tfm *, u8 *, const u8 *) =78 crypto_cipher_alg(tfm)->cia_encrypt;79 unsigned long alignmask = crypto_cipher_alignmask(tfm);80 unsigned int nbytes = walk->nbytes;81 u8 *data = walk->src.virt.addr;82 u8 tmp[XCTR_BLOCKSIZE + MAX_CIPHER_ALIGNMASK];83 u8 *keystream = PTR_ALIGN(tmp + 0, alignmask + 1);84 __le32 ctr32 = cpu_to_le32(byte_ctr / XCTR_BLOCKSIZE + 1);85 86 do {87 crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));88 fn(crypto_cipher_tfm(tfm), keystream, walk->iv);89 crypto_xor(data, keystream, XCTR_BLOCKSIZE);90 crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));91 92 le32_add_cpu(&ctr32, 1);93 94 data += XCTR_BLOCKSIZE;95 } while ((nbytes -= XCTR_BLOCKSIZE) >= XCTR_BLOCKSIZE);96 97 return nbytes;98}99 100static int crypto_xctr_crypt(struct skcipher_request *req)101{102 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);103 struct crypto_cipher *cipher = skcipher_cipher_simple(tfm);104 struct skcipher_walk walk;105 unsigned int nbytes;106 int err;107 u32 byte_ctr = 0;108 109 err = skcipher_walk_virt(&walk, req, false);110 111 while (walk.nbytes >= XCTR_BLOCKSIZE) {112 if (walk.src.virt.addr == walk.dst.virt.addr)113 nbytes = crypto_xctr_crypt_inplace(&walk, cipher,114 byte_ctr);115 else116 nbytes = crypto_xctr_crypt_segment(&walk, cipher,117 byte_ctr);118 119 byte_ctr += walk.nbytes - nbytes;120 err = skcipher_walk_done(&walk, nbytes);121 }122 123 if (walk.nbytes) {124 crypto_xctr_crypt_final(&walk, cipher, byte_ctr);125 err = skcipher_walk_done(&walk, 0);126 }127 128 return err;129}130 131static int crypto_xctr_create(struct crypto_template *tmpl, struct rtattr **tb)132{133 struct skcipher_instance *inst;134 struct crypto_alg *alg;135 int err;136 137 inst = skcipher_alloc_instance_simple(tmpl, tb);138 if (IS_ERR(inst))139 return PTR_ERR(inst);140 141 alg = skcipher_ialg_simple(inst);142 143 /* Block size must be 16 bytes. */144 err = -EINVAL;145 if (alg->cra_blocksize != XCTR_BLOCKSIZE)146 goto out_free_inst;147 148 /* XCTR mode is a stream cipher. */149 inst->alg.base.cra_blocksize = 1;150 151 /*152 * To simplify the implementation, configure the skcipher walk to only153 * give a partial block at the very end, never earlier.154 */155 inst->alg.chunksize = alg->cra_blocksize;156 157 inst->alg.encrypt = crypto_xctr_crypt;158 inst->alg.decrypt = crypto_xctr_crypt;159 160 err = skcipher_register_instance(tmpl, inst);161 if (err) {162out_free_inst:163 inst->free(inst);164 }165 166 return err;167}168 169static struct crypto_template crypto_xctr_tmpl = {170 .name = "xctr",171 .create = crypto_xctr_create,172 .module = THIS_MODULE,173};174 175static int __init crypto_xctr_module_init(void)176{177 return crypto_register_template(&crypto_xctr_tmpl);178}179 180static void __exit crypto_xctr_module_exit(void)181{182 crypto_unregister_template(&crypto_xctr_tmpl);183}184 185subsys_initcall(crypto_xctr_module_init);186module_exit(crypto_xctr_module_exit);187 188MODULE_LICENSE("GPL");189MODULE_DESCRIPTION("XCTR block cipher mode of operation");190MODULE_ALIAS_CRYPTO("xctr");191MODULE_IMPORT_NS(CRYPTO_INTERNAL);192