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, &alg);
59 if (IS_ERR(inst))
60 return PTR_ERR(inst);
61
62 /* OFB mode is a stream cipher. */
63 inst->alg.base.cra_blocksize = 1;
64
65 /*
66 * To simplify the implementation, configure the skcipher walk to only
67 * give a partial block at the very end, never earlier.
68 */
69 inst->alg.chunksize = alg->cra_blocksize;
70
71 inst->alg.encrypt = crypto_ofb_crypt;
72 inst->alg.decrypt = crypto_ofb_crypt;
73
74 err = skcipher_register_instance(tmpl, inst);
75 if (err)
76 inst->free(inst);
77
78 crypto_mod_put(alg);
79 return err;
80}
81
82static struct crypto_template crypto_ofb_tmpl = {
83 .name = "ofb",
84 .create = crypto_ofb_create,
85 .module = THIS_MODULE,
86};
87
88static int __init crypto_ofb_module_init(void)
89{
90 return crypto_register_template(&crypto_ofb_tmpl);
91}
92
93static void __exit crypto_ofb_module_exit(void)
94{
95 crypto_unregister_template(&crypto_ofb_tmpl);
96}
97
98module_init(crypto_ofb_module_init);
99module_exit(crypto_ofb_module_exit);
100
101MODULE_LICENSE("GPL");
102MODULE_DESCRIPTION("OFB block cipher mode of operation");
103MODULE_ALIAS_CRYPTO("ofb");
104