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
55 struct crypto_cts_ctx {
56 struct crypto_skcipher *child;
57 };
58
59 struct crypto_cts_reqctx {
60 struct scatterlist sg[2];
61 unsigned offset;
62 struct skcipher_request subreq;
63 };
64
crypto_cts_reqctx_space(struct skcipher_request * req)65 static 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
crypto_cts_setkey(struct crypto_skcipher * parent,const u8 * key,unsigned int keylen)76 static 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
cts_cbc_crypt_done(struct crypto_async_request * areq,int err)92 static 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
cts_cbc_encrypt(struct skcipher_request * req)102 static 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
crypto_cts_encrypt_done(struct crypto_async_request * areq,int err)132 static 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
143 out:
144 skcipher_request_complete(req, err);
145 }
146
crypto_cts_encrypt(struct skcipher_request * req)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 unsigned int offset;
156
157 skcipher_request_set_tfm(subreq, ctx->child);
158
159 if (nbytes < bsize)
160 return -EINVAL;
161
162 if (nbytes == bsize) {
163 skcipher_request_set_callback(subreq, req->base.flags,
164 req->base.complete,
165 req->base.data);
166 skcipher_request_set_crypt(subreq, req->src, req->dst, nbytes,
167 req->iv);
168 return crypto_skcipher_encrypt(subreq);
169 }
170
171 offset = rounddown(nbytes - 1, bsize);
172 rctx->offset = offset;
173
174 skcipher_request_set_callback(subreq, req->base.flags,
175 crypto_cts_encrypt_done, req);
176 skcipher_request_set_crypt(subreq, req->src, req->dst,
177 offset, req->iv);
178
179 return crypto_skcipher_encrypt(subreq) ?:
180 cts_cbc_encrypt(req);
181 }
182
cts_cbc_decrypt(struct skcipher_request * req)183 static int cts_cbc_decrypt(struct skcipher_request *req)
184 {
185 struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
186 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
187 struct skcipher_request *subreq = &rctx->subreq;
188 int bsize = crypto_skcipher_blocksize(tfm);
189 u8 d[MAX_CIPHER_BLOCKSIZE * 2] __aligned(__alignof__(u32));
190 struct scatterlist *sg;
191 unsigned int offset;
192 u8 *space;
193 int lastn;
194
195 offset = rctx->offset;
196 lastn = req->cryptlen - offset;
197
198 sg = scatterwalk_ffwd(rctx->sg, req->dst, offset - bsize);
199
200 /* 1. Decrypt Cn-1 (s) to create Dn */
201 scatterwalk_map_and_copy(d + bsize, sg, 0, bsize, 0);
202 space = crypto_cts_reqctx_space(req);
203 crypto_xor(d + bsize, space, bsize);
204 /* 2. Pad Cn with zeros at the end to create C of length BB */
205 memset(d, 0, bsize);
206 scatterwalk_map_and_copy(d, req->src, offset, lastn, 0);
207 /* 3. Exclusive-or Dn with C to create Xn */
208 /* 4. Select the first Ln bytes of Xn to create Pn */
209 crypto_xor(d + bsize, d, lastn);
210
211 /* 5. Append the tail (BB - Ln) bytes of Xn to Cn to create En */
212 memcpy(d + lastn, d + bsize + lastn, bsize - lastn);
213 /* 6. Decrypt En to create Pn-1 */
214
215 scatterwalk_map_and_copy(d, sg, 0, bsize + lastn, 1);
216 memzero_explicit(d, sizeof(d));
217
218 skcipher_request_set_callback(subreq, req->base.flags &
219 CRYPTO_TFM_REQ_MAY_BACKLOG,
220 cts_cbc_crypt_done, req);
221
222 skcipher_request_set_crypt(subreq, sg, sg, bsize, space);
223 return crypto_skcipher_decrypt(subreq);
224 }
225
crypto_cts_decrypt_done(struct crypto_async_request * areq,int err)226 static void crypto_cts_decrypt_done(struct crypto_async_request *areq, int err)
227 {
228 struct skcipher_request *req = areq->data;
229
230 if (err)
231 goto out;
232
233 err = cts_cbc_decrypt(req);
234 if (err == -EINPROGRESS || err == -EBUSY)
235 return;
236
237 out:
238 skcipher_request_complete(req, err);
239 }
240
crypto_cts_decrypt(struct skcipher_request * req)241 static int crypto_cts_decrypt(struct skcipher_request *req)
242 {
243 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
244 struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
245 struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
246 struct skcipher_request *subreq = &rctx->subreq;
247 int bsize = crypto_skcipher_blocksize(tfm);
248 unsigned int nbytes = req->cryptlen;
249 unsigned int offset;
250 u8 *space;
251
252 skcipher_request_set_tfm(subreq, ctx->child);
253
254 if (nbytes < bsize)
255 return -EINVAL;
256
257 if (nbytes == bsize) {
258 skcipher_request_set_callback(subreq, req->base.flags,
259 req->base.complete,
260 req->base.data);
261 skcipher_request_set_crypt(subreq, req->src, req->dst, nbytes,
262 req->iv);
263 return crypto_skcipher_decrypt(subreq);
264 }
265
266 skcipher_request_set_callback(subreq, req->base.flags,
267 crypto_cts_decrypt_done, req);
268
269 space = crypto_cts_reqctx_space(req);
270
271 offset = rounddown(nbytes - 1, bsize);
272 rctx->offset = offset;
273
274 if (offset <= bsize)
275 memcpy(space, req->iv, bsize);
276 else
277 scatterwalk_map_and_copy(space, req->src, offset - 2 * bsize,
278 bsize, 0);
279
280 skcipher_request_set_crypt(subreq, req->src, req->dst,
281 offset, req->iv);
282
283 return crypto_skcipher_decrypt(subreq) ?:
284 cts_cbc_decrypt(req);
285 }
286
crypto_cts_init_tfm(struct crypto_skcipher * tfm)287 static int crypto_cts_init_tfm(struct crypto_skcipher *tfm)
288 {
289 struct skcipher_instance *inst = skcipher_alg_instance(tfm);
290 struct crypto_skcipher_spawn *spawn = skcipher_instance_ctx(inst);
291 struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
292 struct crypto_skcipher *cipher;
293 unsigned reqsize;
294 unsigned bsize;
295 unsigned align;
296
297 cipher = crypto_spawn_skcipher(spawn);
298 if (IS_ERR(cipher))
299 return PTR_ERR(cipher);
300
301 ctx->child = cipher;
302
303 align = crypto_skcipher_alignmask(tfm);
304 bsize = crypto_skcipher_blocksize(cipher);
305 reqsize = ALIGN(sizeof(struct crypto_cts_reqctx) +
306 crypto_skcipher_reqsize(cipher),
307 crypto_tfm_ctx_alignment()) +
308 (align & ~(crypto_tfm_ctx_alignment() - 1)) + bsize;
309
310 crypto_skcipher_set_reqsize(tfm, reqsize);
311
312 return 0;
313 }
314
crypto_cts_exit_tfm(struct crypto_skcipher * tfm)315 static void crypto_cts_exit_tfm(struct crypto_skcipher *tfm)
316 {
317 struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
318
319 crypto_free_skcipher(ctx->child);
320 }
321
crypto_cts_free(struct skcipher_instance * inst)322 static void crypto_cts_free(struct skcipher_instance *inst)
323 {
324 crypto_drop_skcipher(skcipher_instance_ctx(inst));
325 kfree(inst);
326 }
327
crypto_cts_create(struct crypto_template * tmpl,struct rtattr ** tb)328 static int crypto_cts_create(struct crypto_template *tmpl, struct rtattr **tb)
329 {
330 struct crypto_skcipher_spawn *spawn;
331 struct skcipher_instance *inst;
332 struct crypto_attr_type *algt;
333 struct skcipher_alg *alg;
334 const char *cipher_name;
335 int err;
336
337 algt = crypto_get_attr_type(tb);
338 if (IS_ERR(algt))
339 return PTR_ERR(algt);
340
341 if ((algt->type ^ CRYPTO_ALG_TYPE_SKCIPHER) & algt->mask)
342 return -EINVAL;
343
344 cipher_name = crypto_attr_alg_name(tb[1]);
345 if (IS_ERR(cipher_name))
346 return PTR_ERR(cipher_name);
347
348 inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL);
349 if (!inst)
350 return -ENOMEM;
351
352 spawn = skcipher_instance_ctx(inst);
353
354 crypto_set_skcipher_spawn(spawn, skcipher_crypto_instance(inst));
355 err = crypto_grab_skcipher(spawn, cipher_name, 0,
356 crypto_requires_sync(algt->type,
357 algt->mask));
358 if (err)
359 goto err_free_inst;
360
361 alg = crypto_spawn_skcipher_alg(spawn);
362
363 err = -EINVAL;
364 if (crypto_skcipher_alg_ivsize(alg) != alg->base.cra_blocksize)
365 goto err_drop_spawn;
366
367 if (strncmp(alg->base.cra_name, "cbc(", 4))
368 goto err_drop_spawn;
369
370 err = crypto_inst_setname(skcipher_crypto_instance(inst), "cts",
371 &alg->base);
372 if (err)
373 goto err_drop_spawn;
374
375 inst->alg.base.cra_flags = alg->base.cra_flags & CRYPTO_ALG_ASYNC;
376 inst->alg.base.cra_priority = alg->base.cra_priority;
377 inst->alg.base.cra_blocksize = alg->base.cra_blocksize;
378 inst->alg.base.cra_alignmask = alg->base.cra_alignmask;
379
380 inst->alg.ivsize = alg->base.cra_blocksize;
381 inst->alg.chunksize = crypto_skcipher_alg_chunksize(alg);
382 inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(alg);
383 inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(alg);
384
385 inst->alg.base.cra_ctxsize = sizeof(struct crypto_cts_ctx);
386
387 inst->alg.init = crypto_cts_init_tfm;
388 inst->alg.exit = crypto_cts_exit_tfm;
389
390 inst->alg.setkey = crypto_cts_setkey;
391 inst->alg.encrypt = crypto_cts_encrypt;
392 inst->alg.decrypt = crypto_cts_decrypt;
393
394 inst->free = crypto_cts_free;
395
396 err = skcipher_register_instance(tmpl, inst);
397 if (err)
398 goto err_drop_spawn;
399
400 out:
401 return err;
402
403 err_drop_spawn:
404 crypto_drop_skcipher(spawn);
405 err_free_inst:
406 kfree(inst);
407 goto out;
408 }
409
410 static struct crypto_template crypto_cts_tmpl = {
411 .name = "cts",
412 .create = crypto_cts_create,
413 .module = THIS_MODULE,
414 };
415
crypto_cts_module_init(void)416 static int __init crypto_cts_module_init(void)
417 {
418 return crypto_register_template(&crypto_cts_tmpl);
419 }
420
crypto_cts_module_exit(void)421 static void __exit crypto_cts_module_exit(void)
422 {
423 crypto_unregister_template(&crypto_cts_tmpl);
424 }
425
426 subsys_initcall(crypto_cts_module_init);
427 module_exit(crypto_cts_module_exit);
428
429 MODULE_LICENSE("Dual BSD/GPL");
430 MODULE_DESCRIPTION("CTS-CBC CipherText Stealing for CBC");
431 MODULE_ALIAS_CRYPTO("cts");
432