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