1// SPDX-License-Identifier: GPL-2.0
  2
  3/*
  4 * OFB: Output FeedBack mode
  5 *
  6 * Copyright (C) 2018 ARM Limited or its affiliates.
  7 * All rights reserved.
  8 */
  9
 10#include <crypto/algapi.h>
 11#include <crypto/internal/cipher.h>
 12#include <crypto/internal/skcipher.h>
 13#include <linux/err.h>
 14#include <linux/init.h>
 15#include <linux/kernel.h>
 16#include <linux/module.h>
 17
 18static int crypto_ofb_crypt(struct skcipher_request *req)
 19{
 20	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 21	struct crypto_cipher *cipher = skcipher_cipher_simple(tfm);
 22	const unsigned int bsize = crypto_cipher_blocksize(cipher);
 23	struct skcipher_walk walk;
 24	int err;
 25
 26	err = skcipher_walk_virt(&walk, req, false);
 27
 28	while (walk.nbytes >= bsize) {
 29		const u8 *src = walk.src.virt.addr;
 30		u8 *dst = walk.dst.virt.addr;
 31		u8 * const iv = walk.iv;
 32		unsigned int nbytes = walk.nbytes;
 33
 34		do {
 35			crypto_cipher_encrypt_one(cipher, iv, iv);
 36			crypto_xor_cpy(dst, src, iv, bsize);
 37			dst += bsize;
 38			src += bsize;
 39		} while ((nbytes -= bsize) >= bsize);
 40
 41		err = skcipher_walk_done(&walk, nbytes);
 42	}
 43
 44	if (walk.nbytes) {
 45		crypto_cipher_encrypt_one(cipher, walk.iv, walk.iv);
 46		crypto_xor_cpy(walk.dst.virt.addr, walk.src.virt.addr, walk.iv,
 47			       walk.nbytes);
 48		err = skcipher_walk_done(&walk, 0);
 49	}
 50	return err;
 51}
 52
 53static int crypto_ofb_create(struct crypto_template *tmpl, struct rtattr **tb)
 54{
 55	struct skcipher_instance *inst;
 56	struct crypto_alg *alg;
 57	int err;
 58
 59	inst = skcipher_alloc_instance_simple(tmpl, tb);
 60	if (IS_ERR(inst))
 61		return PTR_ERR(inst);
 62
 63	alg = skcipher_ialg_simple(inst);
 64
 65	/* OFB mode is a stream cipher. */
 66	inst->alg.base.cra_blocksize = 1;
 67
 68	/*
 69	 * To simplify the implementation, configure the skcipher walk to only
 70	 * give a partial block at the very end, never earlier.
 71	 */
 72	inst->alg.chunksize = alg->cra_blocksize;
 73
 74	inst->alg.encrypt = crypto_ofb_crypt;
 75	inst->alg.decrypt = crypto_ofb_crypt;
 76
 77	err = skcipher_register_instance(tmpl, inst);
 78	if (err)
 79		inst->free(inst);
 80
 81	return err;
 82}
 83
 84static struct crypto_template crypto_ofb_tmpl = {
 85	.name = "ofb",
 86	.create = crypto_ofb_create,
 87	.module = THIS_MODULE,
 88};
 89
 90static int __init crypto_ofb_module_init(void)
 91{
 92	return crypto_register_template(&crypto_ofb_tmpl);
 93}
 94
 95static void __exit crypto_ofb_module_exit(void)
 96{
 97	crypto_unregister_template(&crypto_ofb_tmpl);
 98}
 99
100subsys_initcall(crypto_ofb_module_init);
101module_exit(crypto_ofb_module_exit);
102
103MODULE_LICENSE("GPL");
104MODULE_DESCRIPTION("OFB block cipher mode of operation");
105MODULE_ALIAS_CRYPTO("ofb");
106MODULE_IMPORT_NS(CRYPTO_INTERNAL);