xref: /kernel/linux/linux-5.10/crypto/ofb.c (revision 8c2ecf20) 
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");
105