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
crypto_ofb_crypt(struct skcipher_request * req)17 static 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
crypto_ofb_create(struct crypto_template * tmpl,struct rtattr ** tb)52 static 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
83 static struct crypto_template crypto_ofb_tmpl = {
84 .name = "ofb",
85 .create = crypto_ofb_create,
86 .module = THIS_MODULE,
87 };
88
crypto_ofb_module_init(void)89 static int __init crypto_ofb_module_init(void)
90 {
91 return crypto_register_template(&crypto_ofb_tmpl);
92 }
93
crypto_ofb_module_exit(void)94 static void __exit crypto_ofb_module_exit(void)
95 {
96 crypto_unregister_template(&crypto_ofb_tmpl);
97 }
98
99 subsys_initcall(crypto_ofb_module_init);
100 module_exit(crypto_ofb_module_exit);
101
102 MODULE_LICENSE("GPL");
103 MODULE_DESCRIPTION("OFB block cipher mode of operation");
104 MODULE_ALIAS_CRYPTO("ofb");
105
