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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/internal/skcipher.h>
44 #include <linux/err.h>
45 #include <linux/init.h>
46 #include <linux/kernel.h>
47 #include <linux/log2.h>
48 #include <linux/module.h>
49 #include <linux/scatterlist.h>
50 #include <crypto/scatterwalk.h>
51 #include <linux/slab.h>
52 #include <linux/compiler.h>
53
54 struct crypto_cts_ctx {
55 struct crypto_skcipher *child;
56 };
57
58 struct crypto_cts_reqctx {
59 struct scatterlist sg[2];
60 unsigned offset;
61 struct skcipher_request subreq;
62 };
63
64 static inline u8 *crypto_cts_reqctx_space(struct skcipher_request *req)
65 {
66 struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
67 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
68 struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
69 struct crypto_skcipher *child = ctx->child;
70
71 return PTR_ALIGN((u8 *)(rctx + 1) + crypto_skcipher_reqsize(child),
72 crypto_skcipher_alignmask(tfm) + 1);
73 }
74
75 static int crypto_cts_setkey(struct crypto_skcipher *parent, const u8 *key,
76 unsigned int keylen)
77 {
78 struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(parent);
79 struct crypto_skcipher *child = ctx->child;
80 int err;
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 err = crypto_skcipher_setkey(child, key, keylen);
86 crypto_skcipher_set_flags(parent, crypto_skcipher_get_flags(child) &
87 CRYPTO_TFM_RES_MASK);
88 return err;
89 }
90
91 static void cts_cbc_crypt_done(struct crypto_async_request *areq, int err)
92 {
93 struct skcipher_request *req = areq->data;
94
95 if (err == -EINPROGRESS)
96 return;
97
98 skcipher_request_complete(req, err);
99 }
100
101 static int cts_cbc_encrypt(struct skcipher_request *req)
102 {
103 struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
104 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
105 struct skcipher_request *subreq = &rctx->subreq;
106 int bsize = crypto_skcipher_blocksize(tfm);
107 u8 d[bsize * 2] __aligned(__alignof__(u32));
108 struct scatterlist *sg;
109 unsigned int offset;
110 int lastn;
111
112 offset = rctx->offset;
113 lastn = req->cryptlen - offset;
114
115 sg = scatterwalk_ffwd(rctx->sg, req->dst, offset - bsize);
116 scatterwalk_map_and_copy(d + bsize, sg, 0, bsize, 0);
117
118 memset(d, 0, bsize);
119 scatterwalk_map_and_copy(d, req->src, offset, lastn, 0);
120
121 scatterwalk_map_and_copy(d, sg, 0, bsize + lastn, 1);
122 memzero_explicit(d, sizeof(d));
123
124 skcipher_request_set_callback(subreq, req->base.flags &
125 CRYPTO_TFM_REQ_MAY_BACKLOG,
126 cts_cbc_crypt_done, req);
127 skcipher_request_set_crypt(subreq, sg, sg, bsize, req->iv);
128 return crypto_skcipher_encrypt(subreq);
129 }
130
131 static void crypto_cts_encrypt_done(struct crypto_async_request *areq, int err)
132 {
133 struct skcipher_request *req = areq->data;
134
135 if (err)
136 goto out;
137
138 err = cts_cbc_encrypt(req);
139 if (err == -EINPROGRESS ||
140 (err == -EBUSY && req->base.flags & CRYPTO_TFM_REQ_MAY_BACKLOG))
141 return;
142
143 out:
144 skcipher_request_complete(req, err);
145 }
146
147 static 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
181 static 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[bsize * 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
224 static 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 ||
233 (err == -EBUSY && req->base.flags & CRYPTO_TFM_REQ_MAY_BACKLOG))
234 return;
235
236 out:
237 skcipher_request_complete(req, err);
238 }
239
240 static int crypto_cts_decrypt(struct skcipher_request *req)
241 {
242 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
243 struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
244 struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
245 struct skcipher_request *subreq = &rctx->subreq;
246 int bsize = crypto_skcipher_blocksize(tfm);
247 unsigned int nbytes = req->cryptlen;
248 int cbc_blocks = (nbytes + bsize - 1) / bsize - 1;
249 unsigned int offset;
250 u8 *space;
251
252 skcipher_request_set_tfm(subreq, ctx->child);
253
254 if (cbc_blocks <= 0) {
255 skcipher_request_set_callback(subreq, req->base.flags,
256 req->base.complete,
257 req->base.data);
258 skcipher_request_set_crypt(subreq, req->src, req->dst, nbytes,
259 req->iv);
260 return crypto_skcipher_decrypt(subreq);
261 }
262
263 skcipher_request_set_callback(subreq, req->base.flags,
264 crypto_cts_decrypt_done, req);
265
266 space = crypto_cts_reqctx_space(req);
267
268 offset = cbc_blocks * bsize;
269 rctx->offset = offset;
270
271 if (cbc_blocks <= 1)
272 memcpy(space, req->iv, bsize);
273 else
274 scatterwalk_map_and_copy(space, req->src, offset - 2 * bsize,
275 bsize, 0);
276
277 skcipher_request_set_crypt(subreq, req->src, req->dst,
278 offset, req->iv);
279
280 return crypto_skcipher_decrypt(subreq) ?:
281 cts_cbc_decrypt(req);
282 }
283
284 static int crypto_cts_init_tfm(struct crypto_skcipher *tfm)
285 {
286 struct skcipher_instance *inst = skcipher_alg_instance(tfm);
287 struct crypto_skcipher_spawn *spawn = skcipher_instance_ctx(inst);
288 struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
289 struct crypto_skcipher *cipher;
290 unsigned reqsize;
291 unsigned bsize;
292 unsigned align;
293
294 cipher = crypto_spawn_skcipher(spawn);
295 if (IS_ERR(cipher))
296 return PTR_ERR(cipher);
297
298 ctx->child = cipher;
299
300 align = crypto_skcipher_alignmask(tfm);
301 bsize = crypto_skcipher_blocksize(cipher);
302 reqsize = ALIGN(sizeof(struct crypto_cts_reqctx) +
303 crypto_skcipher_reqsize(cipher),
304 crypto_tfm_ctx_alignment()) +
305 (align & ~(crypto_tfm_ctx_alignment() - 1)) + bsize;
306
307 crypto_skcipher_set_reqsize(tfm, reqsize);
308
309 return 0;
310 }
311
312 static void crypto_cts_exit_tfm(struct crypto_skcipher *tfm)
313 {
314 struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
315
316 crypto_free_skcipher(ctx->child);
317 }
318
319 static void crypto_cts_free(struct skcipher_instance *inst)
320 {
321 crypto_drop_skcipher(skcipher_instance_ctx(inst));
322 kfree(inst);
323 }
324
325 static int crypto_cts_create(struct crypto_template *tmpl, struct rtattr **tb)
326 {
327 struct crypto_skcipher_spawn *spawn;
328 struct skcipher_instance *inst;
329 struct crypto_attr_type *algt;
330 struct skcipher_alg *alg;
331 const char *cipher_name;
332 int err;
333
334 algt = crypto_get_attr_type(tb);
335 if (IS_ERR(algt))
336 return PTR_ERR(algt);
337
338 if ((algt->type ^ CRYPTO_ALG_TYPE_SKCIPHER) & algt->mask)
339 return -EINVAL;
340
341 cipher_name = crypto_attr_alg_name(tb[1]);
342 if (IS_ERR(cipher_name))
343 return PTR_ERR(cipher_name);
344
345 inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL);
346 if (!inst)
347 return -ENOMEM;
348
349 spawn = skcipher_instance_ctx(inst);
350
351 crypto_set_skcipher_spawn(spawn, skcipher_crypto_instance(inst));
352 err = crypto_grab_skcipher(spawn, cipher_name, 0,
353 crypto_requires_sync(algt->type,
354 algt->mask));
355 if (err)
356 goto err_free_inst;
357
358 alg = crypto_spawn_skcipher_alg(spawn);
359
360 err = -EINVAL;
361 if (crypto_skcipher_alg_ivsize(alg) != alg->base.cra_blocksize)
362 goto err_drop_spawn;
363
364 if (strncmp(alg->base.cra_name, "cbc(", 4))
365 goto err_drop_spawn;
366
367 err = crypto_inst_setname(skcipher_crypto_instance(inst), "cts",
368 &alg->base);
369 if (err)
370 goto err_drop_spawn;
371
372 inst->alg.base.cra_flags = alg->base.cra_flags & CRYPTO_ALG_ASYNC;
373 inst->alg.base.cra_priority = alg->base.cra_priority;
374 inst->alg.base.cra_blocksize = alg->base.cra_blocksize;
375 inst->alg.base.cra_alignmask = alg->base.cra_alignmask;
376
377 inst->alg.ivsize = alg->base.cra_blocksize;
378 inst->alg.chunksize = crypto_skcipher_alg_chunksize(alg);
379 inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(alg);
380 inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(alg);
381
382 inst->alg.base.cra_ctxsize = sizeof(struct crypto_cts_ctx);
383
384 inst->alg.init = crypto_cts_init_tfm;
385 inst->alg.exit = crypto_cts_exit_tfm;
386
387 inst->alg.setkey = crypto_cts_setkey;
388 inst->alg.encrypt = crypto_cts_encrypt;
389 inst->alg.decrypt = crypto_cts_decrypt;
390
391 inst->free = crypto_cts_free;
392
393 err = skcipher_register_instance(tmpl, inst);
394 if (err)
395 goto err_drop_spawn;
396
397 out:
398 return err;
399
400 err_drop_spawn:
401 crypto_drop_skcipher(spawn);
402 err_free_inst:
403 kfree(inst);
404 goto out;
405 }
406
407 static struct crypto_template crypto_cts_tmpl = {
408 .name = "cts",
409 .create = crypto_cts_create,
410 .module = THIS_MODULE,
411 };
412
413 static int __init crypto_cts_module_init(void)
414 {
415 return crypto_register_template(&crypto_cts_tmpl);
416 }
417
418 static void __exit crypto_cts_module_exit(void)
419 {
420 crypto_unregister_template(&crypto_cts_tmpl);
421 }
422
423 module_init(crypto_cts_module_init);
424 module_exit(crypto_cts_module_exit);
425
426 MODULE_LICENSE("Dual BSD/GPL");
427 MODULE_DESCRIPTION("CTS-CBC CipherText Stealing for CBC");
428 MODULE_ALIAS_CRYPTO("cts");