1/*
2 * CTS: Cipher Text Stealing mode
3 *
4 * COPYRIGHT (c) 2008
5 * The Regents of the University of Michigan
6 * ALL RIGHTS RESERVED
7 *
8 * Permission is granted to use, copy, create derivative works
9 * and redistribute this software and such derivative works
10 * for any purpose, so long as the name of The University of
11 * Michigan is not used in any advertising or publicity
12 * pertaining to the use of distribution of this software
13 * without specific, written prior authorization.  If the
14 * above copyright notice or any other identification of the
15 * University of Michigan is included in any copy of any
16 * portion of this software, then the disclaimer below must
17 * also be included.
18 *
19 * THIS SOFTWARE IS PROVIDED AS IS, WITHOUT REPRESENTATION
20 * FROM THE UNIVERSITY OF MICHIGAN AS TO ITS FITNESS FOR ANY
21 * PURPOSE, AND WITHOUT WARRANTY BY THE UNIVERSITY OF
22 * MICHIGAN OF ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING
23 * WITHOUT LIMITATION THE IMPLIED WARRANTIES OF
24 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE
25 * REGENTS OF THE UNIVERSITY OF MICHIGAN SHALL NOT BE LIABLE
26 * FOR ANY DAMAGES, INCLUDING SPECIAL, INDIRECT, INCIDENTAL, OR
27 * CONSEQUENTIAL DAMAGES, WITH RESPECT TO ANY CLAIM ARISING
28 * OUT OF OR IN CONNECTION WITH THE USE OF THE SOFTWARE, EVEN
29 * IF IT HAS BEEN OR IS HEREAFTER ADVISED OF THE POSSIBILITY OF
30 * SUCH DAMAGES.
31 */
32
33/* Derived from various:
34 *	Copyright (c) 2006 Herbert Xu <herbert@gondor.apana.org.au>
35 */
36
37/*
38 * This is the Cipher Text Stealing mode as described by
39 * Section 8 of rfc2040 and referenced by rfc3962.
40 * rfc3962 includes errata information in its Appendix A.
41 */
42
43#include <crypto/algapi.h>
44#include <crypto/internal/skcipher.h>
45#include <linux/err.h>
46#include <linux/init.h>
47#include <linux/kernel.h>
48#include <linux/log2.h>
49#include <linux/module.h>
50#include <linux/scatterlist.h>
51#include <crypto/scatterwalk.h>
52#include <linux/slab.h>
53#include <linux/compiler.h>
54
55struct crypto_cts_ctx {
56	struct crypto_skcipher *child;
57};
58
59struct crypto_cts_reqctx {
60	struct scatterlist sg[2];
61	unsigned offset;
62	struct skcipher_request subreq;
63};
64
65static inline u8 *crypto_cts_reqctx_space(struct skcipher_request *req)
66{
67	struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
68	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
69	struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
70	struct crypto_skcipher *child = ctx->child;
71
72	return PTR_ALIGN((u8 *)(rctx + 1) + crypto_skcipher_reqsize(child),
73			 crypto_skcipher_alignmask(tfm) + 1);
74}
75
76static int crypto_cts_setkey(struct crypto_skcipher *parent, const u8 *key,
77			     unsigned int keylen)
78{
79	struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(parent);
80	struct crypto_skcipher *child = ctx->child;
81
82	crypto_skcipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
83	crypto_skcipher_set_flags(child, crypto_skcipher_get_flags(parent) &
84					 CRYPTO_TFM_REQ_MASK);
85	return crypto_skcipher_setkey(child, key, keylen);
86}
87
88static void cts_cbc_crypt_done(void *data, int err)
89{
90	struct skcipher_request *req = data;
91
92	if (err == -EINPROGRESS)
93		return;
94
95	skcipher_request_complete(req, err);
96}
97
98static int cts_cbc_encrypt(struct skcipher_request *req)
99{
100	struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
101	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
102	struct skcipher_request *subreq = &rctx->subreq;
103	int bsize = crypto_skcipher_blocksize(tfm);
104	u8 d[MAX_CIPHER_BLOCKSIZE * 2] __aligned(__alignof__(u32));
105	struct scatterlist *sg;
106	unsigned int offset;
107	int lastn;
108
109	offset = rctx->offset;
110	lastn = req->cryptlen - offset;
111
112	sg = scatterwalk_ffwd(rctx->sg, req->dst, offset - bsize);
113	scatterwalk_map_and_copy(d + bsize, sg, 0, bsize, 0);
114
115	memset(d, 0, bsize);
116	scatterwalk_map_and_copy(d, req->src, offset, lastn, 0);
117
118	scatterwalk_map_and_copy(d, sg, 0, bsize + lastn, 1);
119	memzero_explicit(d, sizeof(d));
120
121	skcipher_request_set_callback(subreq, req->base.flags &
122					      CRYPTO_TFM_REQ_MAY_BACKLOG,
123				      cts_cbc_crypt_done, req);
124	skcipher_request_set_crypt(subreq, sg, sg, bsize, req->iv);
125	return crypto_skcipher_encrypt(subreq);
126}
127
128static void crypto_cts_encrypt_done(void *data, int err)
129{
130	struct skcipher_request *req = data;
131
132	if (err)
133		goto out;
134
135	err = cts_cbc_encrypt(req);
136	if (err == -EINPROGRESS || err == -EBUSY)
137		return;
138
139out:
140	skcipher_request_complete(req, err);
141}
142
143static int crypto_cts_encrypt(struct skcipher_request *req)
144{
145	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
146	struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
147	struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
148	struct skcipher_request *subreq = &rctx->subreq;
149	int bsize = crypto_skcipher_blocksize(tfm);
150	unsigned int nbytes = req->cryptlen;
151	unsigned int offset;
152
153	skcipher_request_set_tfm(subreq, ctx->child);
154
155	if (nbytes < bsize)
156		return -EINVAL;
157
158	if (nbytes == bsize) {
159		skcipher_request_set_callback(subreq, req->base.flags,
160					      req->base.complete,
161					      req->base.data);
162		skcipher_request_set_crypt(subreq, req->src, req->dst, nbytes,
163					   req->iv);
164		return crypto_skcipher_encrypt(subreq);
165	}
166
167	offset = rounddown(nbytes - 1, bsize);
168	rctx->offset = offset;
169
170	skcipher_request_set_callback(subreq, req->base.flags,
171				      crypto_cts_encrypt_done, req);
172	skcipher_request_set_crypt(subreq, req->src, req->dst,
173				   offset, req->iv);
174
175	return crypto_skcipher_encrypt(subreq) ?:
176	       cts_cbc_encrypt(req);
177}
178
179static int cts_cbc_decrypt(struct skcipher_request *req)
180{
181	struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
182	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
183	struct skcipher_request *subreq = &rctx->subreq;
184	int bsize = crypto_skcipher_blocksize(tfm);
185	u8 d[MAX_CIPHER_BLOCKSIZE * 2] __aligned(__alignof__(u32));
186	struct scatterlist *sg;
187	unsigned int offset;
188	u8 *space;
189	int lastn;
190
191	offset = rctx->offset;
192	lastn = req->cryptlen - offset;
193
194	sg = scatterwalk_ffwd(rctx->sg, req->dst, offset - bsize);
195
196	/* 1. Decrypt Cn-1 (s) to create Dn */
197	scatterwalk_map_and_copy(d + bsize, sg, 0, bsize, 0);
198	space = crypto_cts_reqctx_space(req);
199	crypto_xor(d + bsize, space, bsize);
200	/* 2. Pad Cn with zeros at the end to create C of length BB */
201	memset(d, 0, bsize);
202	scatterwalk_map_and_copy(d, req->src, offset, lastn, 0);
203	/* 3. Exclusive-or Dn with C to create Xn */
204	/* 4. Select the first Ln bytes of Xn to create Pn */
205	crypto_xor(d + bsize, d, lastn);
206
207	/* 5. Append the tail (BB - Ln) bytes of Xn to Cn to create En */
208	memcpy(d + lastn, d + bsize + lastn, bsize - lastn);
209	/* 6. Decrypt En to create Pn-1 */
210
211	scatterwalk_map_and_copy(d, sg, 0, bsize + lastn, 1);
212	memzero_explicit(d, sizeof(d));
213
214	skcipher_request_set_callback(subreq, req->base.flags &
215					      CRYPTO_TFM_REQ_MAY_BACKLOG,
216				      cts_cbc_crypt_done, req);
217
218	skcipher_request_set_crypt(subreq, sg, sg, bsize, space);
219	return crypto_skcipher_decrypt(subreq);
220}
221
222static void crypto_cts_decrypt_done(void *data, int err)
223{
224	struct skcipher_request *req = data;
225
226	if (err)
227		goto out;
228
229	err = cts_cbc_decrypt(req);
230	if (err == -EINPROGRESS || err == -EBUSY)
231		return;
232
233out:
234	skcipher_request_complete(req, err);
235}
236
237static int crypto_cts_decrypt(struct skcipher_request *req)
238{
239	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
240	struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
241	struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
242	struct skcipher_request *subreq = &rctx->subreq;
243	int bsize = crypto_skcipher_blocksize(tfm);
244	unsigned int nbytes = req->cryptlen;
245	unsigned int offset;
246	u8 *space;
247
248	skcipher_request_set_tfm(subreq, ctx->child);
249
250	if (nbytes < bsize)
251		return -EINVAL;
252
253	if (nbytes == bsize) {
254		skcipher_request_set_callback(subreq, req->base.flags,
255					      req->base.complete,
256					      req->base.data);
257		skcipher_request_set_crypt(subreq, req->src, req->dst, nbytes,
258					   req->iv);
259		return crypto_skcipher_decrypt(subreq);
260	}
261
262	skcipher_request_set_callback(subreq, req->base.flags,
263				      crypto_cts_decrypt_done, req);
264
265	space = crypto_cts_reqctx_space(req);
266
267	offset = rounddown(nbytes - 1, bsize);
268	rctx->offset = offset;
269
270	if (offset <= bsize)
271		memcpy(space, req->iv, bsize);
272	else
273		scatterwalk_map_and_copy(space, req->src, offset - 2 * bsize,
274					 bsize, 0);
275
276	skcipher_request_set_crypt(subreq, req->src, req->dst,
277				   offset, req->iv);
278
279	return crypto_skcipher_decrypt(subreq) ?:
280	       cts_cbc_decrypt(req);
281}
282
283static int crypto_cts_init_tfm(struct crypto_skcipher *tfm)
284{
285	struct skcipher_instance *inst = skcipher_alg_instance(tfm);
286	struct crypto_skcipher_spawn *spawn = skcipher_instance_ctx(inst);
287	struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
288	struct crypto_skcipher *cipher;
289	unsigned reqsize;
290	unsigned bsize;
291	unsigned align;
292
293	cipher = crypto_spawn_skcipher(spawn);
294	if (IS_ERR(cipher))
295		return PTR_ERR(cipher);
296
297	ctx->child = cipher;
298
299	align = crypto_skcipher_alignmask(tfm);
300	bsize = crypto_skcipher_blocksize(cipher);
301	reqsize = ALIGN(sizeof(struct crypto_cts_reqctx) +
302			crypto_skcipher_reqsize(cipher),
303			crypto_tfm_ctx_alignment()) +
304		  (align & ~(crypto_tfm_ctx_alignment() - 1)) + bsize;
305
306	crypto_skcipher_set_reqsize(tfm, reqsize);
307
308	return 0;
309}
310
311static void crypto_cts_exit_tfm(struct crypto_skcipher *tfm)
312{
313	struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
314
315	crypto_free_skcipher(ctx->child);
316}
317
318static void crypto_cts_free(struct skcipher_instance *inst)
319{
320	crypto_drop_skcipher(skcipher_instance_ctx(inst));
321	kfree(inst);
322}
323
324static int crypto_cts_create(struct crypto_template *tmpl, struct rtattr **tb)
325{
326	struct crypto_skcipher_spawn *spawn;
327	struct skcipher_alg_common *alg;
328	struct skcipher_instance *inst;
329	u32 mask;
330	int err;
331
332	err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_SKCIPHER, &mask);
333	if (err)
334		return err;
335
336	inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL);
337	if (!inst)
338		return -ENOMEM;
339
340	spawn = skcipher_instance_ctx(inst);
341
342	err = crypto_grab_skcipher(spawn, skcipher_crypto_instance(inst),
343				   crypto_attr_alg_name(tb[1]), 0, mask);
344	if (err)
345		goto err_free_inst;
346
347	alg = crypto_spawn_skcipher_alg_common(spawn);
348
349	err = -EINVAL;
350	if (alg->ivsize != alg->base.cra_blocksize)
351		goto err_free_inst;
352
353	if (strncmp(alg->base.cra_name, "cbc(", 4))
354		goto err_free_inst;
355
356	err = crypto_inst_setname(skcipher_crypto_instance(inst), "cts",
357				  &alg->base);
358	if (err)
359		goto err_free_inst;
360
361	inst->alg.base.cra_priority = alg->base.cra_priority;
362	inst->alg.base.cra_blocksize = alg->base.cra_blocksize;
363	inst->alg.base.cra_alignmask = alg->base.cra_alignmask;
364
365	inst->alg.ivsize = alg->base.cra_blocksize;
366	inst->alg.chunksize = alg->chunksize;
367	inst->alg.min_keysize = alg->min_keysize;
368	inst->alg.max_keysize = alg->max_keysize;
369
370	inst->alg.base.cra_ctxsize = sizeof(struct crypto_cts_ctx);
371
372	inst->alg.init = crypto_cts_init_tfm;
373	inst->alg.exit = crypto_cts_exit_tfm;
374
375	inst->alg.setkey = crypto_cts_setkey;
376	inst->alg.encrypt = crypto_cts_encrypt;
377	inst->alg.decrypt = crypto_cts_decrypt;
378
379	inst->free = crypto_cts_free;
380
381	err = skcipher_register_instance(tmpl, inst);
382	if (err) {
383err_free_inst:
384		crypto_cts_free(inst);
385	}
386	return err;
387}
388
389static struct crypto_template crypto_cts_tmpl = {
390	.name = "cts",
391	.create = crypto_cts_create,
392	.module = THIS_MODULE,
393};
394
395static int __init crypto_cts_module_init(void)
396{
397	return crypto_register_template(&crypto_cts_tmpl);
398}
399
400static void __exit crypto_cts_module_exit(void)
401{
402	crypto_unregister_template(&crypto_cts_tmpl);
403}
404
405subsys_initcall(crypto_cts_module_init);
406module_exit(crypto_cts_module_exit);
407
408MODULE_LICENSE("Dual BSD/GPL");
409MODULE_DESCRIPTION("CTS-CBC CipherText Stealing for CBC");
410MODULE_ALIAS_CRYPTO("cts");
411