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 int err;
82
83 crypto_skcipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
84 crypto_skcipher_set_flags(child, crypto_skcipher_get_flags(parent) &
85 CRYPTO_TFM_REQ_MASK);
86 err = crypto_skcipher_setkey(child, key, keylen);
87 crypto_skcipher_set_flags(parent, crypto_skcipher_get_flags(child) &
88 CRYPTO_TFM_RES_MASK);
89 return err;
90}
91
92static void cts_cbc_crypt_done(struct crypto_async_request *areq, int err)
93{
94 struct skcipher_request *req = areq->data;
95
96 if (err == -EINPROGRESS)
97 return;
98
99 skcipher_request_complete(req, err);
100}
101
102static int cts_cbc_encrypt(struct skcipher_request *req)
103{
104 struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
105 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
106 struct skcipher_request *subreq = &rctx->subreq;
107 int bsize = crypto_skcipher_blocksize(tfm);
108 u8 d[MAX_CIPHER_BLOCKSIZE * 2] __aligned(__alignof__(u32));
109 struct scatterlist *sg;
110 unsigned int offset;
111 int lastn;
112
113 offset = rctx->offset;
114 lastn = req->cryptlen - offset;
115
116 sg = scatterwalk_ffwd(rctx->sg, req->dst, offset - bsize);
117 scatterwalk_map_and_copy(d + bsize, sg, 0, bsize, 0);
118
119 memset(d, 0, bsize);
120 scatterwalk_map_and_copy(d, req->src, offset, lastn, 0);
121
122 scatterwalk_map_and_copy(d, sg, 0, bsize + lastn, 1);
123 memzero_explicit(d, sizeof(d));
124
125 skcipher_request_set_callback(subreq, req->base.flags &
126 CRYPTO_TFM_REQ_MAY_BACKLOG,
127 cts_cbc_crypt_done, req);
128 skcipher_request_set_crypt(subreq, sg, sg, bsize, req->iv);
129 return crypto_skcipher_encrypt(subreq);
130}
131
132static void crypto_cts_encrypt_done(struct crypto_async_request *areq, int err)
133{
134 struct skcipher_request *req = areq->data;
135
136 if (err)
137 goto out;
138
139 err = cts_cbc_encrypt(req);
140 if (err == -EINPROGRESS || err == -EBUSY)
141 return;
142
143out:
144 skcipher_request_complete(req, err);
145}
146
147static int crypto_cts_encrypt(struct skcipher_request *req)
148{
149 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
150 struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
151 struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
152 struct skcipher_request *subreq = &rctx->subreq;
153 int bsize = crypto_skcipher_blocksize(tfm);
154 unsigned int nbytes = req->cryptlen;
155 int cbc_blocks = (nbytes + bsize - 1) / bsize - 1;
156 unsigned int offset;
157
158 skcipher_request_set_tfm(subreq, ctx->child);
159
160 if (cbc_blocks <= 0) {
161 skcipher_request_set_callback(subreq, req->base.flags,
162 req->base.complete,
163 req->base.data);
164 skcipher_request_set_crypt(subreq, req->src, req->dst, nbytes,
165 req->iv);
166 return crypto_skcipher_encrypt(subreq);
167 }
168
169 offset = cbc_blocks * bsize;
170 rctx->offset = offset;
171
172 skcipher_request_set_callback(subreq, req->base.flags,
173 crypto_cts_encrypt_done, req);
174 skcipher_request_set_crypt(subreq, req->src, req->dst,
175 offset, req->iv);
176
177 return crypto_skcipher_encrypt(subreq) ?:
178 cts_cbc_encrypt(req);
179}
180
181static int cts_cbc_decrypt(struct skcipher_request *req)
182{
183 struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
184 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
185 struct skcipher_request *subreq = &rctx->subreq;
186 int bsize = crypto_skcipher_blocksize(tfm);
187 u8 d[MAX_CIPHER_BLOCKSIZE * 2] __aligned(__alignof__(u32));
188 struct scatterlist *sg;
189 unsigned int offset;
190 u8 *space;
191 int lastn;
192
193 offset = rctx->offset;
194 lastn = req->cryptlen - offset;
195
196 sg = scatterwalk_ffwd(rctx->sg, req->dst, offset - bsize);
197
198 /* 1. Decrypt Cn-1 (s) to create Dn */
199 scatterwalk_map_and_copy(d + bsize, sg, 0, bsize, 0);
200 space = crypto_cts_reqctx_space(req);
201 crypto_xor(d + bsize, space, bsize);
202 /* 2. Pad Cn with zeros at the end to create C of length BB */
203 memset(d, 0, bsize);
204 scatterwalk_map_and_copy(d, req->src, offset, lastn, 0);
205 /* 3. Exclusive-or Dn with C to create Xn */
206 /* 4. Select the first Ln bytes of Xn to create Pn */
207 crypto_xor(d + bsize, d, lastn);
208
209 /* 5. Append the tail (BB - Ln) bytes of Xn to Cn to create En */
210 memcpy(d + lastn, d + bsize + lastn, bsize - lastn);
211 /* 6. Decrypt En to create Pn-1 */
212
213 scatterwalk_map_and_copy(d, sg, 0, bsize + lastn, 1);
214 memzero_explicit(d, sizeof(d));
215
216 skcipher_request_set_callback(subreq, req->base.flags &
217 CRYPTO_TFM_REQ_MAY_BACKLOG,
218 cts_cbc_crypt_done, req);
219
220 skcipher_request_set_crypt(subreq, sg, sg, bsize, space);
221 return crypto_skcipher_decrypt(subreq);
222}
223
224static void crypto_cts_decrypt_done(struct crypto_async_request *areq, int err)
225{
226 struct skcipher_request *req = areq->data;
227
228 if (err)
229 goto out;
230
231 err = cts_cbc_decrypt(req);
232 if (err == -EINPROGRESS || err == -EBUSY)
233 return;
234
235out:
236 skcipher_request_complete(req, err);
237}
238
239static int crypto_cts_decrypt(struct skcipher_request *req)
240{
241 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
242 struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
243 struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
244 struct skcipher_request *subreq = &rctx->subreq;
245 int bsize = crypto_skcipher_blocksize(tfm);
246 unsigned int nbytes = req->cryptlen;
247 int cbc_blocks = (nbytes + bsize - 1) / bsize - 1;
248 unsigned int offset;
249 u8 *space;
250
251 skcipher_request_set_tfm(subreq, ctx->child);
252
253 if (cbc_blocks <= 0) {
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 = cbc_blocks * bsize;
268 rctx->offset = offset;
269
270 if (cbc_blocks <= 1)
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_instance *inst;
328 struct crypto_attr_type *algt;
329 struct skcipher_alg *alg;
330 const char *cipher_name;
331 int err;
332
333 algt = crypto_get_attr_type(tb);
334 if (IS_ERR(algt))
335 return PTR_ERR(algt);
336
337 if ((algt->type ^ CRYPTO_ALG_TYPE_SKCIPHER) & algt->mask)
338 return -EINVAL;
339
340 cipher_name = crypto_attr_alg_name(tb[1]);
341 if (IS_ERR(cipher_name))
342 return PTR_ERR(cipher_name);
343
344 inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL);
345 if (!inst)
346 return -ENOMEM;
347
348 spawn = skcipher_instance_ctx(inst);
349
350 crypto_set_skcipher_spawn(spawn, skcipher_crypto_instance(inst));
351 err = crypto_grab_skcipher(spawn, cipher_name, 0,
352 crypto_requires_sync(algt->type,
353 algt->mask));
354 if (err)
355 goto err_free_inst;
356
357 alg = crypto_spawn_skcipher_alg(spawn);
358
359 err = -EINVAL;
360 if (crypto_skcipher_alg_ivsize(alg) != alg->base.cra_blocksize)
361 goto err_drop_spawn;
362
363 if (strncmp(alg->base.cra_name, "cbc(", 4))
364 goto err_drop_spawn;
365
366 err = crypto_inst_setname(skcipher_crypto_instance(inst), "cts",
367 &alg->base);
368 if (err)
369 goto err_drop_spawn;
370
371 inst->alg.base.cra_flags = alg->base.cra_flags & CRYPTO_ALG_ASYNC;
372 inst->alg.base.cra_priority = alg->base.cra_priority;
373 inst->alg.base.cra_blocksize = alg->base.cra_blocksize;
374 inst->alg.base.cra_alignmask = alg->base.cra_alignmask;
375
376 inst->alg.ivsize = alg->base.cra_blocksize;
377 inst->alg.chunksize = crypto_skcipher_alg_chunksize(alg);
378 inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(alg);
379 inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(alg);
380
381 inst->alg.base.cra_ctxsize = sizeof(struct crypto_cts_ctx);
382
383 inst->alg.init = crypto_cts_init_tfm;
384 inst->alg.exit = crypto_cts_exit_tfm;
385
386 inst->alg.setkey = crypto_cts_setkey;
387 inst->alg.encrypt = crypto_cts_encrypt;
388 inst->alg.decrypt = crypto_cts_decrypt;
389
390 inst->free = crypto_cts_free;
391
392 err = skcipher_register_instance(tmpl, inst);
393 if (err)
394 goto err_drop_spawn;
395
396out:
397 return err;
398
399err_drop_spawn:
400 crypto_drop_skcipher(spawn);
401err_free_inst:
402 kfree(inst);
403 goto out;
404}
405
406static struct crypto_template crypto_cts_tmpl = {
407 .name = "cts",
408 .create = crypto_cts_create,
409 .module = THIS_MODULE,
410};
411
412static int __init crypto_cts_module_init(void)
413{
414 return crypto_register_template(&crypto_cts_tmpl);
415}
416
417static void __exit crypto_cts_module_exit(void)
418{
419 crypto_unregister_template(&crypto_cts_tmpl);
420}
421
422module_init(crypto_cts_module_init);
423module_exit(crypto_cts_module_exit);
424
425MODULE_LICENSE("Dual BSD/GPL");
426MODULE_DESCRIPTION("CTS-CBC CipherText Stealing for CBC");
427MODULE_ALIAS_CRYPTO("cts");
428