xref: /kernel/linux/linux-6.6/crypto/ofb.c (revision 62306a36) 
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);
107