1 /*
2 * Key Wrapping: RFC3394 / NIST SP800-38F
3 *
4 * Copyright (C) 2015, Stephan Mueller <smueller@chronox.de>
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, and the entire permission notice in its entirety,
11 * including the disclaimer of warranties.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 * 3. The name of the author may not be used to endorse or promote
16 * products derived from this software without specific prior
17 * written permission.
18 *
19 * ALTERNATIVELY, this product may be distributed under the terms of
20 * the GNU General Public License, in which case the provisions of the GPL2
21 * are required INSTEAD OF the above restrictions. (This clause is
22 * necessary due to a potential bad interaction between the GPL and
23 * the restrictions contained in a BSD-style copyright.)
24 *
25 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
26 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
27 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF
28 * WHICH ARE HEREBY DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE
29 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
30 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
31 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
32 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
33 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
34 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
35 * USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH
36 * DAMAGE.
37 */
38
39 /*
40 * Note for using key wrapping:
41 *
42 * * The result of the encryption operation is the ciphertext starting
43 * with the 2nd semiblock. The first semiblock is provided as the IV.
44 * The IV used to start the encryption operation is the default IV.
45 *
46 * * The input for the decryption is the first semiblock handed in as an
47 * IV. The ciphertext is the data starting with the 2nd semiblock. The
48 * return code of the decryption operation will be EBADMSG in case an
49 * integrity error occurs.
50 *
51 * To obtain the full result of an encryption as expected by SP800-38F, the
52 * caller must allocate a buffer of plaintext + 8 bytes:
53 *
54 * unsigned int datalen = ptlen + crypto_skcipher_ivsize(tfm);
55 * u8 data[datalen];
56 * u8 *iv = data;
57 * u8 *pt = data + crypto_skcipher_ivsize(tfm);
58 * <ensure that pt contains the plaintext of size ptlen>
59 * sg_init_one(&sg, ptdata, ptlen);
60 * skcipher_request_set_crypt(req, &sg, &sg, ptlen, iv);
61 *
62 * ==> After encryption, data now contains full KW result as per SP800-38F.
63 *
64 * In case of decryption, ciphertext now already has the expected length
65 * and must be segmented appropriately:
66 *
67 * unsigned int datalen = CTLEN;
68 * u8 data[datalen];
69 * <ensure that data contains full ciphertext>
70 * u8 *iv = data;
71 * u8 *ct = data + crypto_skcipher_ivsize(tfm);
72 * unsigned int ctlen = datalen - crypto_skcipher_ivsize(tfm);
73 * sg_init_one(&sg, ctdata, ctlen);
74 * skcipher_request_set_crypt(req, &sg, &sg, ptlen, iv);
75 *
76 * ==> After decryption (which hopefully does not return EBADMSG), the ct
77 * pointer now points to the plaintext of size ctlen.
78 *
79 * Note 2: KWP is not implemented as this would defy in-place operation.
80 * If somebody wants to wrap non-aligned data, he should simply pad
81 * the input with zeros to fill it up to the 8 byte boundary.
82 */
83
84 #include <linux/module.h>
85 #include <linux/crypto.h>
86 #include <linux/scatterlist.h>
87 #include <crypto/scatterwalk.h>
88 #include <crypto/internal/skcipher.h>
89
90 struct crypto_kw_ctx {
91 struct crypto_cipher *child;
92 };
93
94 struct crypto_kw_block {
95 #define SEMIBSIZE 8
96 __be64 A;
97 __be64 R;
98 };
99
100 /*
101 * Fast forward the SGL to the "end" length minus SEMIBSIZE.
102 * The start in the SGL defined by the fast-forward is returned with
103 * the walk variable
104 */
crypto_kw_scatterlist_ff(struct scatter_walk * walk,struct scatterlist * sg,unsigned int end)105 static void crypto_kw_scatterlist_ff(struct scatter_walk *walk,
106 struct scatterlist *sg,
107 unsigned int end)
108 {
109 unsigned int skip = 0;
110
111 /* The caller should only operate on full SEMIBLOCKs. */
112 BUG_ON(end < SEMIBSIZE);
113
114 skip = end - SEMIBSIZE;
115 while (sg) {
116 if (sg->length > skip) {
117 scatterwalk_start(walk, sg);
118 scatterwalk_advance(walk, skip);
119 break;
120 } else
121 skip -= sg->length;
122
123 sg = sg_next(sg);
124 }
125 }
126
crypto_kw_decrypt(struct blkcipher_desc * desc,struct scatterlist * dst,struct scatterlist * src,unsigned int nbytes)127 static int crypto_kw_decrypt(struct blkcipher_desc *desc,
128 struct scatterlist *dst, struct scatterlist *src,
129 unsigned int nbytes)
130 {
131 struct crypto_blkcipher *tfm = desc->tfm;
132 struct crypto_kw_ctx *ctx = crypto_blkcipher_ctx(tfm);
133 struct crypto_cipher *child = ctx->child;
134 struct crypto_kw_block block;
135 struct scatterlist *lsrc, *ldst;
136 u64 t = 6 * ((nbytes) >> 3);
137 unsigned int i;
138 int ret = 0;
139
140 /*
141 * Require at least 2 semiblocks (note, the 3rd semiblock that is
142 * required by SP800-38F is the IV.
143 */
144 if (nbytes < (2 * SEMIBSIZE) || nbytes % SEMIBSIZE)
145 return -EINVAL;
146
147 /* Place the IV into block A */
148 memcpy(&block.A, desc->info, SEMIBSIZE);
149
150 /*
151 * src scatterlist is read-only. dst scatterlist is r/w. During the
152 * first loop, lsrc points to src and ldst to dst. For any
153 * subsequent round, the code operates on dst only.
154 */
155 lsrc = src;
156 ldst = dst;
157
158 for (i = 0; i < 6; i++) {
159 struct scatter_walk src_walk, dst_walk;
160 unsigned int tmp_nbytes = nbytes;
161
162 while (tmp_nbytes) {
163 /* move pointer by tmp_nbytes in the SGL */
164 crypto_kw_scatterlist_ff(&src_walk, lsrc, tmp_nbytes);
165 /* get the source block */
166 scatterwalk_copychunks(&block.R, &src_walk, SEMIBSIZE,
167 false);
168
169 /* perform KW operation: modify IV with counter */
170 block.A ^= cpu_to_be64(t);
171 t--;
172 /* perform KW operation: decrypt block */
173 crypto_cipher_decrypt_one(child, (u8*)&block,
174 (u8*)&block);
175
176 /* move pointer by tmp_nbytes in the SGL */
177 crypto_kw_scatterlist_ff(&dst_walk, ldst, tmp_nbytes);
178 /* Copy block->R into place */
179 scatterwalk_copychunks(&block.R, &dst_walk, SEMIBSIZE,
180 true);
181
182 tmp_nbytes -= SEMIBSIZE;
183 }
184
185 /* we now start to operate on the dst SGL only */
186 lsrc = dst;
187 ldst = dst;
188 }
189
190 /* Perform authentication check */
191 if (block.A != cpu_to_be64(0xa6a6a6a6a6a6a6a6ULL))
192 ret = -EBADMSG;
193
194 memzero_explicit(&block, sizeof(struct crypto_kw_block));
195
196 return ret;
197 }
198
crypto_kw_encrypt(struct blkcipher_desc * desc,struct scatterlist * dst,struct scatterlist * src,unsigned int nbytes)199 static int crypto_kw_encrypt(struct blkcipher_desc *desc,
200 struct scatterlist *dst, struct scatterlist *src,
201 unsigned int nbytes)
202 {
203 struct crypto_blkcipher *tfm = desc->tfm;
204 struct crypto_kw_ctx *ctx = crypto_blkcipher_ctx(tfm);
205 struct crypto_cipher *child = ctx->child;
206 struct crypto_kw_block block;
207 struct scatterlist *lsrc, *ldst;
208 u64 t = 1;
209 unsigned int i;
210
211 /*
212 * Require at least 2 semiblocks (note, the 3rd semiblock that is
213 * required by SP800-38F is the IV that occupies the first semiblock.
214 * This means that the dst memory must be one semiblock larger than src.
215 * Also ensure that the given data is aligned to semiblock.
216 */
217 if (nbytes < (2 * SEMIBSIZE) || nbytes % SEMIBSIZE)
218 return -EINVAL;
219
220 /*
221 * Place the predefined IV into block A -- for encrypt, the caller
222 * does not need to provide an IV, but he needs to fetch the final IV.
223 */
224 block.A = cpu_to_be64(0xa6a6a6a6a6a6a6a6ULL);
225
226 /*
227 * src scatterlist is read-only. dst scatterlist is r/w. During the
228 * first loop, lsrc points to src and ldst to dst. For any
229 * subsequent round, the code operates on dst only.
230 */
231 lsrc = src;
232 ldst = dst;
233
234 for (i = 0; i < 6; i++) {
235 struct scatter_walk src_walk, dst_walk;
236 unsigned int tmp_nbytes = nbytes;
237
238 scatterwalk_start(&src_walk, lsrc);
239 scatterwalk_start(&dst_walk, ldst);
240
241 while (tmp_nbytes) {
242 /* get the source block */
243 scatterwalk_copychunks(&block.R, &src_walk, SEMIBSIZE,
244 false);
245
246 /* perform KW operation: encrypt block */
247 crypto_cipher_encrypt_one(child, (u8 *)&block,
248 (u8 *)&block);
249 /* perform KW operation: modify IV with counter */
250 block.A ^= cpu_to_be64(t);
251 t++;
252
253 /* Copy block->R into place */
254 scatterwalk_copychunks(&block.R, &dst_walk, SEMIBSIZE,
255 true);
256
257 tmp_nbytes -= SEMIBSIZE;
258 }
259
260 /* we now start to operate on the dst SGL only */
261 lsrc = dst;
262 ldst = dst;
263 }
264
265 /* establish the IV for the caller to pick up */
266 memcpy(desc->info, &block.A, SEMIBSIZE);
267
268 memzero_explicit(&block, sizeof(struct crypto_kw_block));
269
270 return 0;
271 }
272
crypto_kw_setkey(struct crypto_tfm * parent,const u8 * key,unsigned int keylen)273 static int crypto_kw_setkey(struct crypto_tfm *parent, const u8 *key,
274 unsigned int keylen)
275 {
276 struct crypto_kw_ctx *ctx = crypto_tfm_ctx(parent);
277 struct crypto_cipher *child = ctx->child;
278 int err;
279
280 crypto_cipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
281 crypto_cipher_set_flags(child, crypto_tfm_get_flags(parent) &
282 CRYPTO_TFM_REQ_MASK);
283 err = crypto_cipher_setkey(child, key, keylen);
284 crypto_tfm_set_flags(parent, crypto_cipher_get_flags(child) &
285 CRYPTO_TFM_RES_MASK);
286 return err;
287 }
288
crypto_kw_init_tfm(struct crypto_tfm * tfm)289 static int crypto_kw_init_tfm(struct crypto_tfm *tfm)
290 {
291 struct crypto_instance *inst = crypto_tfm_alg_instance(tfm);
292 struct crypto_spawn *spawn = crypto_instance_ctx(inst);
293 struct crypto_kw_ctx *ctx = crypto_tfm_ctx(tfm);
294 struct crypto_cipher *cipher;
295
296 cipher = crypto_spawn_cipher(spawn);
297 if (IS_ERR(cipher))
298 return PTR_ERR(cipher);
299
300 ctx->child = cipher;
301 return 0;
302 }
303
crypto_kw_exit_tfm(struct crypto_tfm * tfm)304 static void crypto_kw_exit_tfm(struct crypto_tfm *tfm)
305 {
306 struct crypto_kw_ctx *ctx = crypto_tfm_ctx(tfm);
307
308 crypto_free_cipher(ctx->child);
309 }
310
crypto_kw_alloc(struct rtattr ** tb)311 static struct crypto_instance *crypto_kw_alloc(struct rtattr **tb)
312 {
313 struct crypto_instance *inst = NULL;
314 struct crypto_alg *alg = NULL;
315 int err;
316
317 err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_BLKCIPHER);
318 if (err)
319 return ERR_PTR(err);
320
321 alg = crypto_get_attr_alg(tb, CRYPTO_ALG_TYPE_CIPHER,
322 CRYPTO_ALG_TYPE_MASK);
323 if (IS_ERR(alg))
324 return ERR_CAST(alg);
325
326 inst = ERR_PTR(-EINVAL);
327 /* Section 5.1 requirement for KW */
328 if (alg->cra_blocksize != sizeof(struct crypto_kw_block))
329 goto err;
330
331 inst = crypto_alloc_instance("kw", alg);
332 if (IS_ERR(inst))
333 goto err;
334
335 inst->alg.cra_flags = CRYPTO_ALG_TYPE_BLKCIPHER;
336 inst->alg.cra_priority = alg->cra_priority;
337 inst->alg.cra_blocksize = SEMIBSIZE;
338 inst->alg.cra_alignmask = 0;
339 inst->alg.cra_type = &crypto_blkcipher_type;
340 inst->alg.cra_blkcipher.ivsize = SEMIBSIZE;
341 inst->alg.cra_blkcipher.min_keysize = alg->cra_cipher.cia_min_keysize;
342 inst->alg.cra_blkcipher.max_keysize = alg->cra_cipher.cia_max_keysize;
343
344 inst->alg.cra_ctxsize = sizeof(struct crypto_kw_ctx);
345
346 inst->alg.cra_init = crypto_kw_init_tfm;
347 inst->alg.cra_exit = crypto_kw_exit_tfm;
348
349 inst->alg.cra_blkcipher.setkey = crypto_kw_setkey;
350 inst->alg.cra_blkcipher.encrypt = crypto_kw_encrypt;
351 inst->alg.cra_blkcipher.decrypt = crypto_kw_decrypt;
352
353 err:
354 crypto_mod_put(alg);
355 return inst;
356 }
357
crypto_kw_free(struct crypto_instance * inst)358 static void crypto_kw_free(struct crypto_instance *inst)
359 {
360 crypto_drop_spawn(crypto_instance_ctx(inst));
361 kfree(inst);
362 }
363
364 static struct crypto_template crypto_kw_tmpl = {
365 .name = "kw",
366 .alloc = crypto_kw_alloc,
367 .free = crypto_kw_free,
368 .module = THIS_MODULE,
369 };
370
crypto_kw_init(void)371 static int __init crypto_kw_init(void)
372 {
373 return crypto_register_template(&crypto_kw_tmpl);
374 }
375
crypto_kw_exit(void)376 static void __exit crypto_kw_exit(void)
377 {
378 crypto_unregister_template(&crypto_kw_tmpl);
379 }
380
381 module_init(crypto_kw_init);
382 module_exit(crypto_kw_exit);
383
384 MODULE_LICENSE("Dual BSD/GPL");
385 MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");
386 MODULE_DESCRIPTION("Key Wrapping (RFC3394 / NIST SP800-38F)");
387 MODULE_ALIAS_CRYPTO("kw");
388
