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 <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_blkcipher *child;
55 };
56
57 static int crypto_cts_setkey(struct crypto_tfm *parent, const u8 *key,
58 unsigned int keylen)
59 {
60 struct crypto_cts_ctx *ctx = crypto_tfm_ctx(parent);
61 struct crypto_blkcipher *child = ctx->child;
62 int err;
63
64 crypto_blkcipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
65 crypto_blkcipher_set_flags(child, crypto_tfm_get_flags(parent) &
66 CRYPTO_TFM_REQ_MASK);
67 err = crypto_blkcipher_setkey(child, key, keylen);
68 crypto_tfm_set_flags(parent, crypto_blkcipher_get_flags(child) &
69 CRYPTO_TFM_RES_MASK);
70 return err;
71 }
72
73 static int cts_cbc_encrypt(struct crypto_cts_ctx *ctx,
74 struct blkcipher_desc *desc,
75 struct scatterlist *dst,
76 struct scatterlist *src,
77 unsigned int offset,
78 unsigned int nbytes)
79 {
80 int bsize = crypto_blkcipher_blocksize(desc->tfm);
81 u8 tmp[bsize], tmp2[bsize];
82 struct blkcipher_desc lcldesc;
83 struct scatterlist sgsrc[1], sgdst[1];
84 int lastn = nbytes - bsize;
85 u8 iv[bsize];
86 u8 s[bsize * 2], d[bsize * 2];
87 int err;
88
89 if (lastn < 0)
90 return -EINVAL;
91
92 sg_init_table(sgsrc, 1);
93 sg_init_table(sgdst, 1);
94
95 memset(s, 0, sizeof(s));
96 scatterwalk_map_and_copy(s, src, offset, nbytes, 0);
97
98 memcpy(iv, desc->info, bsize);
99
100 lcldesc.tfm = ctx->child;
101 lcldesc.info = iv;
102 lcldesc.flags = desc->flags;
103
104 sg_set_buf(&sgsrc[0], s, bsize);
105 sg_set_buf(&sgdst[0], tmp, bsize);
106 err = crypto_blkcipher_encrypt_iv(&lcldesc, sgdst, sgsrc, bsize);
107
108 memcpy(d + bsize, tmp, lastn);
109
110 lcldesc.info = tmp;
111
112 sg_set_buf(&sgsrc[0], s + bsize, bsize);
113 sg_set_buf(&sgdst[0], tmp2, bsize);
114 err = crypto_blkcipher_encrypt_iv(&lcldesc, sgdst, sgsrc, bsize);
115
116 memcpy(d, tmp2, bsize);
117
118 scatterwalk_map_and_copy(d, dst, offset, nbytes, 1);
119
120 memcpy(desc->info, tmp2, bsize);
121
122 return err;
123 }
124
125 static int crypto_cts_encrypt(struct blkcipher_desc *desc,
126 struct scatterlist *dst, struct scatterlist *src,
127 unsigned int nbytes)
128 {
129 struct crypto_cts_ctx *ctx = crypto_blkcipher_ctx(desc->tfm);
130 int bsize = crypto_blkcipher_blocksize(desc->tfm);
131 int tot_blocks = (nbytes + bsize - 1) / bsize;
132 int cbc_blocks = tot_blocks > 2 ? tot_blocks - 2 : 0;
133 struct blkcipher_desc lcldesc;
134 int err;
135
136 lcldesc.tfm = ctx->child;
137 lcldesc.info = desc->info;
138 lcldesc.flags = desc->flags;
139
140 if (tot_blocks == 1) {
141 err = crypto_blkcipher_encrypt_iv(&lcldesc, dst, src, bsize);
142 } else if (nbytes <= bsize * 2) {
143 err = cts_cbc_encrypt(ctx, desc, dst, src, 0, nbytes);
144 } else {
145 /* do normal function for tot_blocks - 2 */
146 err = crypto_blkcipher_encrypt_iv(&lcldesc, dst, src,
147 cbc_blocks * bsize);
148 if (err == 0) {
149 /* do cts for final two blocks */
150 err = cts_cbc_encrypt(ctx, desc, dst, src,
151 cbc_blocks * bsize,
152 nbytes - (cbc_blocks * bsize));
153 }
154 }
155
156 return err;
157 }
158
159 static int cts_cbc_decrypt(struct crypto_cts_ctx *ctx,
160 struct blkcipher_desc *desc,
161 struct scatterlist *dst,
162 struct scatterlist *src,
163 unsigned int offset,
164 unsigned int nbytes)
165 {
166 int bsize = crypto_blkcipher_blocksize(desc->tfm);
167 u8 tmp[bsize];
168 struct blkcipher_desc lcldesc;
169 struct scatterlist sgsrc[1], sgdst[1];
170 int lastn = nbytes - bsize;
171 u8 iv[bsize];
172 u8 s[bsize * 2], d[bsize * 2];
173 int err;
174
175 if (lastn < 0)
176 return -EINVAL;
177
178 sg_init_table(sgsrc, 1);
179 sg_init_table(sgdst, 1);
180
181 scatterwalk_map_and_copy(s, src, offset, nbytes, 0);
182
183 lcldesc.tfm = ctx->child;
184 lcldesc.info = iv;
185 lcldesc.flags = desc->flags;
186
187 /* 1. Decrypt Cn-1 (s) to create Dn (tmp)*/
188 memset(iv, 0, sizeof(iv));
189 sg_set_buf(&sgsrc[0], s, bsize);
190 sg_set_buf(&sgdst[0], tmp, bsize);
191 err = crypto_blkcipher_decrypt_iv(&lcldesc, sgdst, sgsrc, bsize);
192 if (err)
193 return err;
194 /* 2. Pad Cn with zeros at the end to create C of length BB */
195 memset(iv, 0, sizeof(iv));
196 memcpy(iv, s + bsize, lastn);
197 /* 3. Exclusive-or Dn (tmp) with C (iv) to create Xn (tmp) */
198 crypto_xor(tmp, iv, bsize);
199 /* 4. Select the first Ln bytes of Xn (tmp) to create Pn */
200 memcpy(d + bsize, tmp, lastn);
201
202 /* 5. Append the tail (BB - Ln) bytes of Xn (tmp) to Cn to create En */
203 memcpy(s + bsize + lastn, tmp + lastn, bsize - lastn);
204 /* 6. Decrypt En to create Pn-1 */
205 memset(iv, 0, sizeof(iv));
206 sg_set_buf(&sgsrc[0], s + bsize, bsize);
207 sg_set_buf(&sgdst[0], d, bsize);
208 err = crypto_blkcipher_decrypt_iv(&lcldesc, sgdst, sgsrc, bsize);
209
210 /* XOR with previous block */
211 crypto_xor(d, desc->info, bsize);
212
213 scatterwalk_map_and_copy(d, dst, offset, nbytes, 1);
214
215 memcpy(desc->info, s, bsize);
216 return err;
217 }
218
219 static int crypto_cts_decrypt(struct blkcipher_desc *desc,
220 struct scatterlist *dst, struct scatterlist *src,
221 unsigned int nbytes)
222 {
223 struct crypto_cts_ctx *ctx = crypto_blkcipher_ctx(desc->tfm);
224 int bsize = crypto_blkcipher_blocksize(desc->tfm);
225 int tot_blocks = (nbytes + bsize - 1) / bsize;
226 int cbc_blocks = tot_blocks > 2 ? tot_blocks - 2 : 0;
227 struct blkcipher_desc lcldesc;
228 int err;
229
230 lcldesc.tfm = ctx->child;
231 lcldesc.info = desc->info;
232 lcldesc.flags = desc->flags;
233
234 if (tot_blocks == 1) {
235 err = crypto_blkcipher_decrypt_iv(&lcldesc, dst, src, bsize);
236 } else if (nbytes <= bsize * 2) {
237 err = cts_cbc_decrypt(ctx, desc, dst, src, 0, nbytes);
238 } else {
239 /* do normal function for tot_blocks - 2 */
240 err = crypto_blkcipher_decrypt_iv(&lcldesc, dst, src,
241 cbc_blocks * bsize);
242 if (err == 0) {
243 /* do cts for final two blocks */
244 err = cts_cbc_decrypt(ctx, desc, dst, src,
245 cbc_blocks * bsize,
246 nbytes - (cbc_blocks * bsize));
247 }
248 }
249 return err;
250 }
251
252 static int crypto_cts_init_tfm(struct crypto_tfm *tfm)
253 {
254 struct crypto_instance *inst = (void *)tfm->__crt_alg;
255 struct crypto_spawn *spawn = crypto_instance_ctx(inst);
256 struct crypto_cts_ctx *ctx = crypto_tfm_ctx(tfm);
257 struct crypto_blkcipher *cipher;
258
259 cipher = crypto_spawn_blkcipher(spawn);
260 if (IS_ERR(cipher))
261 return PTR_ERR(cipher);
262
263 ctx->child = cipher;
264 return 0;
265 }
266
267 static void crypto_cts_exit_tfm(struct crypto_tfm *tfm)
268 {
269 struct crypto_cts_ctx *ctx = crypto_tfm_ctx(tfm);
270 crypto_free_blkcipher(ctx->child);
271 }
272
273 static struct crypto_instance *crypto_cts_alloc(struct rtattr **tb)
274 {
275 struct crypto_instance *inst;
276 struct crypto_alg *alg;
277 int err;
278
279 err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_BLKCIPHER);
280 if (err)
281 return ERR_PTR(err);
282
283 alg = crypto_attr_alg(tb[1], CRYPTO_ALG_TYPE_BLKCIPHER,
284 CRYPTO_ALG_TYPE_MASK);
285 err = PTR_ERR(alg);
286 if (IS_ERR(alg))
287 return ERR_PTR(err);
288
289 inst = ERR_PTR(-EINVAL);
290 if (!is_power_of_2(alg->cra_blocksize))
291 goto out_put_alg;
292
293 inst = crypto_alloc_instance("cts", alg);
294 if (IS_ERR(inst))
295 goto out_put_alg;
296
297 inst->alg.cra_flags = CRYPTO_ALG_TYPE_BLKCIPHER;
298 inst->alg.cra_priority = alg->cra_priority;
299 inst->alg.cra_blocksize = alg->cra_blocksize;
300 inst->alg.cra_alignmask = alg->cra_alignmask;
301 inst->alg.cra_type = &crypto_blkcipher_type;
302
303 /* We access the data as u32s when xoring. */
304 inst->alg.cra_alignmask |= __alignof__(u32) - 1;
305
306 inst->alg.cra_blkcipher.ivsize = alg->cra_blocksize;
307 inst->alg.cra_blkcipher.min_keysize = alg->cra_blkcipher.min_keysize;
308 inst->alg.cra_blkcipher.max_keysize = alg->cra_blkcipher.max_keysize;
309
310 inst->alg.cra_blkcipher.geniv = "seqiv";
311
312 inst->alg.cra_ctxsize = sizeof(struct crypto_cts_ctx);
313
314 inst->alg.cra_init = crypto_cts_init_tfm;
315 inst->alg.cra_exit = crypto_cts_exit_tfm;
316
317 inst->alg.cra_blkcipher.setkey = crypto_cts_setkey;
318 inst->alg.cra_blkcipher.encrypt = crypto_cts_encrypt;
319 inst->alg.cra_blkcipher.decrypt = crypto_cts_decrypt;
320
321 out_put_alg:
322 crypto_mod_put(alg);
323 return inst;
324 }
325
326 static void crypto_cts_free(struct crypto_instance *inst)
327 {
328 crypto_drop_spawn(crypto_instance_ctx(inst));
329 kfree(inst);
330 }
331
332 static struct crypto_template crypto_cts_tmpl = {
333 .name = "cts",
334 .alloc = crypto_cts_alloc,
335 .free = crypto_cts_free,
336 .module = THIS_MODULE,
337 };
338
339 static int __init crypto_cts_module_init(void)
340 {
341 return crypto_register_template(&crypto_cts_tmpl);
342 }
343
344 static void __exit crypto_cts_module_exit(void)
345 {
346 crypto_unregister_template(&crypto_cts_tmpl);
347 }
348
349 module_init(crypto_cts_module_init);
350 module_exit(crypto_cts_module_exit);
351
352 MODULE_LICENSE("Dual BSD/GPL");
353 MODULE_DESCRIPTION("CTS-CBC CipherText Stealing for CBC");
354
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