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Linux/crypto/cts.c

  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 
 53 struct crypto_cts_ctx {
 54         struct crypto_skcipher *child;
 55 };
 56 
 57 struct crypto_cts_reqctx {
 58         struct scatterlist sg[2];
 59         unsigned offset;
 60         struct skcipher_request subreq;
 61 };
 62 
 63 static inline u8 *crypto_cts_reqctx_space(struct skcipher_request *req)
 64 {
 65         struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
 66         struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 67         struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
 68         struct crypto_skcipher *child = ctx->child;
 69 
 70         return PTR_ALIGN((u8 *)(rctx + 1) + crypto_skcipher_reqsize(child),
 71                          crypto_skcipher_alignmask(tfm) + 1);
 72 }
 73 
 74 static int crypto_cts_setkey(struct crypto_skcipher *parent, const u8 *key,
 75                              unsigned int keylen)
 76 {
 77         struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(parent);
 78         struct crypto_skcipher *child = ctx->child;
 79         int err;
 80 
 81         crypto_skcipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
 82         crypto_skcipher_set_flags(child, crypto_skcipher_get_flags(parent) &
 83                                          CRYPTO_TFM_REQ_MASK);
 84         err = crypto_skcipher_setkey(child, key, keylen);
 85         crypto_skcipher_set_flags(parent, crypto_skcipher_get_flags(child) &
 86                                           CRYPTO_TFM_RES_MASK);
 87         return err;
 88 }
 89 
 90 static void cts_cbc_crypt_done(struct crypto_async_request *areq, int err)
 91 {
 92         struct skcipher_request *req = areq->data;
 93 
 94         if (err == -EINPROGRESS)
 95                 return;
 96 
 97         skcipher_request_complete(req, err);
 98 }
 99 
100 static int cts_cbc_encrypt(struct skcipher_request *req)
101 {
102         struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
103         struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
104         struct skcipher_request *subreq = &rctx->subreq;
105         int bsize = crypto_skcipher_blocksize(tfm);
106         u8 d[bsize * 2] __attribute__ ((aligned(__alignof__(u32))));
107         struct scatterlist *sg;
108         unsigned int offset;
109         int lastn;
110 
111         offset = rctx->offset;
112         lastn = req->cryptlen - offset;
113 
114         sg = scatterwalk_ffwd(rctx->sg, req->dst, offset - bsize);
115         scatterwalk_map_and_copy(d + bsize, sg, 0, bsize, 0);
116 
117         memset(d, 0, bsize);
118         scatterwalk_map_and_copy(d, req->src, offset, lastn, 0);
119 
120         scatterwalk_map_and_copy(d, sg, 0, bsize + lastn, 1);
121         memzero_explicit(d, sizeof(d));
122 
123         skcipher_request_set_callback(subreq, req->base.flags &
124                                               CRYPTO_TFM_REQ_MAY_BACKLOG,
125                                       cts_cbc_crypt_done, req);
126         skcipher_request_set_crypt(subreq, sg, sg, bsize, req->iv);
127         return crypto_skcipher_encrypt(subreq);
128 }
129 
130 static void crypto_cts_encrypt_done(struct crypto_async_request *areq, int err)
131 {
132         struct skcipher_request *req = areq->data;
133 
134         if (err)
135                 goto out;
136 
137         err = cts_cbc_encrypt(req);
138         if (err == -EINPROGRESS ||
139             (err == -EBUSY && req->base.flags & CRYPTO_TFM_REQ_MAY_BACKLOG))
140                 return;
141 
142 out:
143         skcipher_request_complete(req, err);
144 }
145 
146 static int crypto_cts_encrypt(struct skcipher_request *req)
147 {
148         struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
149         struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
150         struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
151         struct skcipher_request *subreq = &rctx->subreq;
152         int bsize = crypto_skcipher_blocksize(tfm);
153         unsigned int nbytes = req->cryptlen;
154         int cbc_blocks = (nbytes + bsize - 1) / bsize - 1;
155         unsigned int offset;
156 
157         skcipher_request_set_tfm(subreq, ctx->child);
158 
159         if (cbc_blocks <= 0) {
160                 skcipher_request_set_callback(subreq, req->base.flags,
161                                               req->base.complete,
162                                               req->base.data);
163                 skcipher_request_set_crypt(subreq, req->src, req->dst, nbytes,
164                                            req->iv);
165                 return crypto_skcipher_encrypt(subreq);
166         }
167 
168         offset = cbc_blocks * bsize;
169         rctx->offset = offset;
170 
171         skcipher_request_set_callback(subreq, req->base.flags,
172                                       crypto_cts_encrypt_done, req);
173         skcipher_request_set_crypt(subreq, req->src, req->dst,
174                                    offset, req->iv);
175 
176         return crypto_skcipher_encrypt(subreq) ?:
177                cts_cbc_encrypt(req);
178 }
179 
180 static int cts_cbc_decrypt(struct skcipher_request *req)
181 {
182         struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
183         struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
184         struct skcipher_request *subreq = &rctx->subreq;
185         int bsize = crypto_skcipher_blocksize(tfm);
186         u8 d[bsize * 2] __attribute__ ((aligned(__alignof__(u32))));
187         struct scatterlist *sg;
188         unsigned int offset;
189         u8 *space;
190         int lastn;
191 
192         offset = rctx->offset;
193         lastn = req->cryptlen - offset;
194 
195         sg = scatterwalk_ffwd(rctx->sg, req->dst, offset - bsize);
196 
197         /* 1. Decrypt Cn-1 (s) to create Dn */
198         scatterwalk_map_and_copy(d + bsize, sg, 0, bsize, 0);
199         space = crypto_cts_reqctx_space(req);
200         crypto_xor(d + bsize, space, bsize);
201         /* 2. Pad Cn with zeros at the end to create C of length BB */
202         memset(d, 0, bsize);
203         scatterwalk_map_and_copy(d, req->src, offset, lastn, 0);
204         /* 3. Exclusive-or Dn with C to create Xn */
205         /* 4. Select the first Ln bytes of Xn to create Pn */
206         crypto_xor(d + bsize, d, lastn);
207 
208         /* 5. Append the tail (BB - Ln) bytes of Xn to Cn to create En */
209         memcpy(d + lastn, d + bsize + lastn, bsize - lastn);
210         /* 6. Decrypt En to create Pn-1 */
211 
212         scatterwalk_map_and_copy(d, sg, 0, bsize + lastn, 1);
213         memzero_explicit(d, sizeof(d));
214 
215         skcipher_request_set_callback(subreq, req->base.flags &
216                                               CRYPTO_TFM_REQ_MAY_BACKLOG,
217                                       cts_cbc_crypt_done, req);
218 
219         skcipher_request_set_crypt(subreq, sg, sg, bsize, space);
220         return crypto_skcipher_decrypt(subreq);
221 }
222 
223 static void crypto_cts_decrypt_done(struct crypto_async_request *areq, int err)
224 {
225         struct skcipher_request *req = areq->data;
226 
227         if (err)
228                 goto out;
229 
230         err = cts_cbc_decrypt(req);
231         if (err == -EINPROGRESS ||
232             (err == -EBUSY && req->base.flags & CRYPTO_TFM_REQ_MAY_BACKLOG))
233                 return;
234 
235 out:
236         skcipher_request_complete(req, err);
237 }
238 
239 static 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 
283 static 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 
311 static 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 
318 static void crypto_cts_free(struct skcipher_instance *inst)
319 {
320         crypto_drop_skcipher(skcipher_instance_ctx(inst));
321         kfree(inst);
322 }
323 
324 static 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         /* We access the data as u32s when xoring. */
377         inst->alg.base.cra_alignmask |= __alignof__(u32) - 1;
378 
379         inst->alg.ivsize = alg->base.cra_blocksize;
380         inst->alg.chunksize = crypto_skcipher_alg_chunksize(alg);
381         inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(alg);
382         inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(alg);
383 
384         inst->alg.base.cra_ctxsize = sizeof(struct crypto_cts_ctx);
385 
386         inst->alg.init = crypto_cts_init_tfm;
387         inst->alg.exit = crypto_cts_exit_tfm;
388 
389         inst->alg.setkey = crypto_cts_setkey;
390         inst->alg.encrypt = crypto_cts_encrypt;
391         inst->alg.decrypt = crypto_cts_decrypt;
392 
393         inst->free = crypto_cts_free;
394 
395         err = skcipher_register_instance(tmpl, inst);
396         if (err)
397                 goto err_drop_spawn;
398 
399 out:
400         return err;
401 
402 err_drop_spawn:
403         crypto_drop_skcipher(spawn);
404 err_free_inst:
405         kfree(inst);
406         goto out;
407 }
408 
409 static struct crypto_template crypto_cts_tmpl = {
410         .name = "cts",
411         .create = crypto_cts_create,
412         .module = THIS_MODULE,
413 };
414 
415 static int __init crypto_cts_module_init(void)
416 {
417         return crypto_register_template(&crypto_cts_tmpl);
418 }
419 
420 static void __exit crypto_cts_module_exit(void)
421 {
422         crypto_unregister_template(&crypto_cts_tmpl);
423 }
424 
425 module_init(crypto_cts_module_init);
426 module_exit(crypto_cts_module_exit);
427 
428 MODULE_LICENSE("Dual BSD/GPL");
429 MODULE_DESCRIPTION("CTS-CBC CipherText Stealing for CBC");
430 MODULE_ALIAS_CRYPTO("cts");
431 

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