1 //SPDX-License-Identifier: GPL-2.0
2 /*
3 * CFB: Cipher FeedBack mode
4 *
5 * Copyright (c) 2018 James.Bottomley@HansenPartnership.com
6 *
7 * CFB is a stream cipher mode which is layered on to a block
8 * encryption scheme. It works very much like a one time pad where
9 * the pad is generated initially from the encrypted IV and then
10 * subsequently from the encrypted previous block of ciphertext. The
11 * pad is XOR'd into the plain text to get the final ciphertext.
12 *
13 * The scheme of CFB is best described by wikipedia:
14 *
15 * https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#CFB
16 *
17 * Note that since the pad for both encryption and decryption is
18 * generated by an encryption operation, CFB never uses the block
19 * decryption function.
20 */
21
22 #include <crypto/algapi.h>
23 #include <crypto/internal/cipher.h>
24 #include <crypto/internal/skcipher.h>
25 #include <linux/err.h>
26 #include <linux/init.h>
27 #include <linux/kernel.h>
28 #include <linux/module.h>
29 #include <linux/string.h>
30
crypto_cfb_bsize(struct crypto_skcipher * tfm)31 static unsigned int crypto_cfb_bsize(struct crypto_skcipher *tfm)
32 {
33 return crypto_cipher_blocksize(skcipher_cipher_simple(tfm));
34 }
35
crypto_cfb_encrypt_one(struct crypto_skcipher * tfm,const u8 * src,u8 * dst)36 static void crypto_cfb_encrypt_one(struct crypto_skcipher *tfm,
37 const u8 *src, u8 *dst)
38 {
39 crypto_cipher_encrypt_one(skcipher_cipher_simple(tfm), dst, src);
40 }
41
42 /* final encrypt and decrypt is the same */
crypto_cfb_final(struct skcipher_walk * walk,struct crypto_skcipher * tfm)43 static void crypto_cfb_final(struct skcipher_walk *walk,
44 struct crypto_skcipher *tfm)
45 {
46 const unsigned long alignmask = crypto_skcipher_alignmask(tfm);
47 u8 tmp[MAX_CIPHER_BLOCKSIZE + MAX_CIPHER_ALIGNMASK];
48 u8 *stream = PTR_ALIGN(tmp + 0, alignmask + 1);
49 u8 *src = walk->src.virt.addr;
50 u8 *dst = walk->dst.virt.addr;
51 u8 *iv = walk->iv;
52 unsigned int nbytes = walk->nbytes;
53
54 crypto_cfb_encrypt_one(tfm, iv, stream);
55 crypto_xor_cpy(dst, stream, src, nbytes);
56 }
57
crypto_cfb_encrypt_segment(struct skcipher_walk * walk,struct crypto_skcipher * tfm)58 static int crypto_cfb_encrypt_segment(struct skcipher_walk *walk,
59 struct crypto_skcipher *tfm)
60 {
61 const unsigned int bsize = crypto_cfb_bsize(tfm);
62 unsigned int nbytes = walk->nbytes;
63 u8 *src = walk->src.virt.addr;
64 u8 *dst = walk->dst.virt.addr;
65 u8 *iv = walk->iv;
66
67 do {
68 crypto_cfb_encrypt_one(tfm, iv, dst);
69 crypto_xor(dst, src, bsize);
70 iv = dst;
71
72 src += bsize;
73 dst += bsize;
74 } while ((nbytes -= bsize) >= bsize);
75
76 memcpy(walk->iv, iv, bsize);
77
78 return nbytes;
79 }
80
crypto_cfb_encrypt_inplace(struct skcipher_walk * walk,struct crypto_skcipher * tfm)81 static int crypto_cfb_encrypt_inplace(struct skcipher_walk *walk,
82 struct crypto_skcipher *tfm)
83 {
84 const unsigned int bsize = crypto_cfb_bsize(tfm);
85 unsigned int nbytes = walk->nbytes;
86 u8 *src = walk->src.virt.addr;
87 u8 *iv = walk->iv;
88 u8 tmp[MAX_CIPHER_BLOCKSIZE];
89
90 do {
91 crypto_cfb_encrypt_one(tfm, iv, tmp);
92 crypto_xor(src, tmp, bsize);
93 iv = src;
94
95 src += bsize;
96 } while ((nbytes -= bsize) >= bsize);
97
98 memcpy(walk->iv, iv, bsize);
99
100 return nbytes;
101 }
102
crypto_cfb_encrypt(struct skcipher_request * req)103 static int crypto_cfb_encrypt(struct skcipher_request *req)
104 {
105 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
106 struct skcipher_walk walk;
107 unsigned int bsize = crypto_cfb_bsize(tfm);
108 int err;
109
110 err = skcipher_walk_virt(&walk, req, false);
111
112 while (walk.nbytes >= bsize) {
113 if (walk.src.virt.addr == walk.dst.virt.addr)
114 err = crypto_cfb_encrypt_inplace(&walk, tfm);
115 else
116 err = crypto_cfb_encrypt_segment(&walk, tfm);
117 err = skcipher_walk_done(&walk, err);
118 }
119
120 if (walk.nbytes) {
121 crypto_cfb_final(&walk, tfm);
122 err = skcipher_walk_done(&walk, 0);
123 }
124
125 return err;
126 }
127
crypto_cfb_decrypt_segment(struct skcipher_walk * walk,struct crypto_skcipher * tfm)128 static int crypto_cfb_decrypt_segment(struct skcipher_walk *walk,
129 struct crypto_skcipher *tfm)
130 {
131 const unsigned int bsize = crypto_cfb_bsize(tfm);
132 unsigned int nbytes = walk->nbytes;
133 u8 *src = walk->src.virt.addr;
134 u8 *dst = walk->dst.virt.addr;
135 u8 *iv = walk->iv;
136
137 do {
138 crypto_cfb_encrypt_one(tfm, iv, dst);
139 crypto_xor(dst, src, bsize);
140 iv = src;
141
142 src += bsize;
143 dst += bsize;
144 } while ((nbytes -= bsize) >= bsize);
145
146 memcpy(walk->iv, iv, bsize);
147
148 return nbytes;
149 }
150
crypto_cfb_decrypt_inplace(struct skcipher_walk * walk,struct crypto_skcipher * tfm)151 static int crypto_cfb_decrypt_inplace(struct skcipher_walk *walk,
152 struct crypto_skcipher *tfm)
153 {
154 const unsigned int bsize = crypto_cfb_bsize(tfm);
155 unsigned int nbytes = walk->nbytes;
156 u8 *src = walk->src.virt.addr;
157 u8 * const iv = walk->iv;
158 u8 tmp[MAX_CIPHER_BLOCKSIZE];
159
160 do {
161 crypto_cfb_encrypt_one(tfm, iv, tmp);
162 memcpy(iv, src, bsize);
163 crypto_xor(src, tmp, bsize);
164 src += bsize;
165 } while ((nbytes -= bsize) >= bsize);
166
167 return nbytes;
168 }
169
crypto_cfb_decrypt_blocks(struct skcipher_walk * walk,struct crypto_skcipher * tfm)170 static int crypto_cfb_decrypt_blocks(struct skcipher_walk *walk,
171 struct crypto_skcipher *tfm)
172 {
173 if (walk->src.virt.addr == walk->dst.virt.addr)
174 return crypto_cfb_decrypt_inplace(walk, tfm);
175 else
176 return crypto_cfb_decrypt_segment(walk, tfm);
177 }
178
crypto_cfb_decrypt(struct skcipher_request * req)179 static int crypto_cfb_decrypt(struct skcipher_request *req)
180 {
181 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
182 struct skcipher_walk walk;
183 const unsigned int bsize = crypto_cfb_bsize(tfm);
184 int err;
185
186 err = skcipher_walk_virt(&walk, req, false);
187
188 while (walk.nbytes >= bsize) {
189 err = crypto_cfb_decrypt_blocks(&walk, tfm);
190 err = skcipher_walk_done(&walk, err);
191 }
192
193 if (walk.nbytes) {
194 crypto_cfb_final(&walk, tfm);
195 err = skcipher_walk_done(&walk, 0);
196 }
197
198 return err;
199 }
200
crypto_cfb_create(struct crypto_template * tmpl,struct rtattr ** tb)201 static int crypto_cfb_create(struct crypto_template *tmpl, struct rtattr **tb)
202 {
203 struct skcipher_instance *inst;
204 struct crypto_alg *alg;
205 int err;
206
207 inst = skcipher_alloc_instance_simple(tmpl, tb);
208 if (IS_ERR(inst))
209 return PTR_ERR(inst);
210
211 alg = skcipher_ialg_simple(inst);
212
213 /* CFB mode is a stream cipher. */
214 inst->alg.base.cra_blocksize = 1;
215
216 /*
217 * To simplify the implementation, configure the skcipher walk to only
218 * give a partial block at the very end, never earlier.
219 */
220 inst->alg.chunksize = alg->cra_blocksize;
221
222 inst->alg.encrypt = crypto_cfb_encrypt;
223 inst->alg.decrypt = crypto_cfb_decrypt;
224
225 err = skcipher_register_instance(tmpl, inst);
226 if (err)
227 inst->free(inst);
228
229 return err;
230 }
231
232 static struct crypto_template crypto_cfb_tmpl = {
233 .name = "cfb",
234 .create = crypto_cfb_create,
235 .module = THIS_MODULE,
236 };
237
crypto_cfb_module_init(void)238 static int __init crypto_cfb_module_init(void)
239 {
240 return crypto_register_template(&crypto_cfb_tmpl);
241 }
242
crypto_cfb_module_exit(void)243 static void __exit crypto_cfb_module_exit(void)
244 {
245 crypto_unregister_template(&crypto_cfb_tmpl);
246 }
247
248 subsys_initcall(crypto_cfb_module_init);
249 module_exit(crypto_cfb_module_exit);
250
251 MODULE_LICENSE("GPL");
252 MODULE_DESCRIPTION("CFB block cipher mode of operation");
253 MODULE_ALIAS_CRYPTO("cfb");
254 MODULE_IMPORT_NS(CRYPTO_INTERNAL);
255
