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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
90struct crypto_kw_ctx {
91 struct crypto_cipher *child;
92};
93
94struct crypto_kw_block {
95#define SEMIBSIZE 8
96 u8 A[SEMIBSIZE];
97 u8 R[SEMIBSIZE];
98};
99
100/* convert 64 bit integer into its string representation */
101static inline void crypto_kw_cpu_to_be64(u64 val, u8 *buf)
102{
103 __be64 *a = (__be64 *)buf;
104
105 *a = cpu_to_be64(val);
106}
107
108/*
109 * Fast forward the SGL to the "end" length minus SEMIBSIZE.
110 * The start in the SGL defined by the fast-forward is returned with
111 * the walk variable
112 */
113static void crypto_kw_scatterlist_ff(struct scatter_walk *walk,
114 struct scatterlist *sg,
115 unsigned int end)
116{
117 unsigned int skip = 0;
118
119 /* The caller should only operate on full SEMIBLOCKs. */
120 BUG_ON(end < SEMIBSIZE);
121
122 skip = end - SEMIBSIZE;
123 while (sg) {
124 if (sg->length > skip) {
125 scatterwalk_start(walk, sg);
126 scatterwalk_advance(walk, skip);
127 break;
128 } else
129 skip -= sg->length;
130
131 sg = sg_next(sg);
132 }
133}
134
135static int crypto_kw_decrypt(struct blkcipher_desc *desc,
136 struct scatterlist *dst, struct scatterlist *src,
137 unsigned int nbytes)
138{
139 struct crypto_blkcipher *tfm = desc->tfm;
140 struct crypto_kw_ctx *ctx = crypto_blkcipher_ctx(tfm);
141 struct crypto_cipher *child = ctx->child;
142
143 unsigned long alignmask = max_t(unsigned long, SEMIBSIZE,
144 crypto_cipher_alignmask(child));
145 unsigned int i;
146
147 u8 blockbuf[sizeof(struct crypto_kw_block) + alignmask];
148 struct crypto_kw_block *block = (struct crypto_kw_block *)
149 PTR_ALIGN(blockbuf + 0, alignmask + 1);
150
151 u64 t = 6 * ((nbytes) >> 3);
152 struct scatterlist *lsrc, *ldst;
153 int ret = 0;
154
155 /*
156 * Require at least 2 semiblocks (note, the 3rd semiblock that is
157 * required by SP800-38F is the IV.
158 */
159 if (nbytes < (2 * SEMIBSIZE) || nbytes % SEMIBSIZE)
160 return -EINVAL;
161
162 /* Place the IV into block A */
163 memcpy(block->A, desc->info, SEMIBSIZE);
164
165 /*
166 * src scatterlist is read-only. dst scatterlist is r/w. During the
167 * first loop, lsrc points to src and ldst to dst. For any
168 * subsequent round, the code operates on dst only.
169 */
170 lsrc = src;
171 ldst = dst;
172
173 for (i = 0; i < 6; i++) {
174 u8 tbe_buffer[SEMIBSIZE + alignmask];
175 /* alignment for the crypto_xor and the _to_be64 operation */
176 u8 *tbe = PTR_ALIGN(tbe_buffer + 0, alignmask + 1);
177 unsigned int tmp_nbytes = nbytes;
178 struct scatter_walk src_walk, dst_walk;
179
180 while (tmp_nbytes) {
181 /* move pointer by tmp_nbytes in the SGL */
182 crypto_kw_scatterlist_ff(&src_walk, lsrc, tmp_nbytes);
183 /* get the source block */
184 scatterwalk_copychunks(block->R, &src_walk, SEMIBSIZE,
185 false);
186
187 /* perform KW operation: get counter as byte string */
188 crypto_kw_cpu_to_be64(t, tbe);
189 /* perform KW operation: modify IV with counter */
190 crypto_xor(block->A, tbe, SEMIBSIZE);
191 t--;
192 /* perform KW operation: decrypt block */
193 crypto_cipher_decrypt_one(child, (u8*)block,
194 (u8*)block);
195
196 /* move pointer by tmp_nbytes in the SGL */
197 crypto_kw_scatterlist_ff(&dst_walk, ldst, tmp_nbytes);
198 /* Copy block->R into place */
199 scatterwalk_copychunks(block->R, &dst_walk, SEMIBSIZE,
200 true);
201
202 tmp_nbytes -= SEMIBSIZE;
203 }
204
205 /* we now start to operate on the dst SGL only */
206 lsrc = dst;
207 ldst = dst;
208 }
209
210 /* Perform authentication check */
211 if (crypto_memneq("\xA6\xA6\xA6\xA6\xA6\xA6\xA6\xA6", block->A,
212 SEMIBSIZE))
213 ret = -EBADMSG;
214
215 memzero_explicit(block, sizeof(struct crypto_kw_block));
216
217 return ret;
218}
219
220static int crypto_kw_encrypt(struct blkcipher_desc *desc,
221 struct scatterlist *dst, struct scatterlist *src,
222 unsigned int nbytes)
223{
224 struct crypto_blkcipher *tfm = desc->tfm;
225 struct crypto_kw_ctx *ctx = crypto_blkcipher_ctx(tfm);
226 struct crypto_cipher *child = ctx->child;
227
228 unsigned long alignmask = max_t(unsigned long, SEMIBSIZE,
229 crypto_cipher_alignmask(child));
230 unsigned int i;
231
232 u8 blockbuf[sizeof(struct crypto_kw_block) + alignmask];
233 struct crypto_kw_block *block = (struct crypto_kw_block *)
234 PTR_ALIGN(blockbuf + 0, alignmask + 1);
235
236 u64 t = 1;
237 struct scatterlist *lsrc, *ldst;
238
239 /*
240 * Require at least 2 semiblocks (note, the 3rd semiblock that is
241 * required by SP800-38F is the IV that occupies the first semiblock.
242 * This means that the dst memory must be one semiblock larger than src.
243 * Also ensure that the given data is aligned to semiblock.
244 */
245 if (nbytes < (2 * SEMIBSIZE) || nbytes % SEMIBSIZE)
246 return -EINVAL;
247
248 /*
249 * Place the predefined IV into block A -- for encrypt, the caller
250 * does not need to provide an IV, but he needs to fetch the final IV.
251 */
252 memcpy(block->A, "\xA6\xA6\xA6\xA6\xA6\xA6\xA6\xA6", SEMIBSIZE);
253
254 /*
255 * src scatterlist is read-only. dst scatterlist is r/w. During the
256 * first loop, lsrc points to src and ldst to dst. For any
257 * subsequent round, the code operates on dst only.
258 */
259 lsrc = src;
260 ldst = dst;
261
262 for (i = 0; i < 6; i++) {
263 u8 tbe_buffer[SEMIBSIZE + alignmask];
264 u8 *tbe = PTR_ALIGN(tbe_buffer + 0, alignmask + 1);
265 unsigned int tmp_nbytes = nbytes;
266 struct scatter_walk src_walk, dst_walk;
267
268 scatterwalk_start(&src_walk, lsrc);
269 scatterwalk_start(&dst_walk, ldst);
270
271 while (tmp_nbytes) {
272 /* get the source block */
273 scatterwalk_copychunks(block->R, &src_walk, SEMIBSIZE,
274 false);
275
276 /* perform KW operation: encrypt block */
277 crypto_cipher_encrypt_one(child, (u8 *)block,
278 (u8 *)block);
279 /* perform KW operation: get counter as byte string */
280 crypto_kw_cpu_to_be64(t, tbe);
281 /* perform KW operation: modify IV with counter */
282 crypto_xor(block->A, tbe, SEMIBSIZE);
283 t++;
284
285 /* Copy block->R into place */
286 scatterwalk_copychunks(block->R, &dst_walk, SEMIBSIZE,
287 true);
288
289 tmp_nbytes -= SEMIBSIZE;
290 }
291
292 /* we now start to operate on the dst SGL only */
293 lsrc = dst;
294 ldst = dst;
295 }
296
297 /* establish the IV for the caller to pick up */
298 memcpy(desc->info, block->A, SEMIBSIZE);
299
300 memzero_explicit(block, sizeof(struct crypto_kw_block));
301
302 return 0;
303}
304
305static int crypto_kw_setkey(struct crypto_tfm *parent, const u8 *key,
306 unsigned int keylen)
307{
308 struct crypto_kw_ctx *ctx = crypto_tfm_ctx(parent);
309 struct crypto_cipher *child = ctx->child;
310 int err;
311
312 crypto_cipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
313 crypto_cipher_set_flags(child, crypto_tfm_get_flags(parent) &
314 CRYPTO_TFM_REQ_MASK);
315 err = crypto_cipher_setkey(child, key, keylen);
316 crypto_tfm_set_flags(parent, crypto_cipher_get_flags(child) &
317 CRYPTO_TFM_RES_MASK);
318 return err;
319}
320
321static int crypto_kw_init_tfm(struct crypto_tfm *tfm)
322{
323 struct crypto_instance *inst = crypto_tfm_alg_instance(tfm);
324 struct crypto_spawn *spawn = crypto_instance_ctx(inst);
325 struct crypto_kw_ctx *ctx = crypto_tfm_ctx(tfm);
326 struct crypto_cipher *cipher;
327
328 cipher = crypto_spawn_cipher(spawn);
329 if (IS_ERR(cipher))
330 return PTR_ERR(cipher);
331
332 ctx->child = cipher;
333 return 0;
334}
335
336static void crypto_kw_exit_tfm(struct crypto_tfm *tfm)
337{
338 struct crypto_kw_ctx *ctx = crypto_tfm_ctx(tfm);
339
340 crypto_free_cipher(ctx->child);
341}
342
343static struct crypto_instance *crypto_kw_alloc(struct rtattr **tb)
344{
345 struct crypto_instance *inst = NULL;
346 struct crypto_alg *alg = NULL;
347 int err;
348
349 err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_BLKCIPHER);
350 if (err)
351 return ERR_PTR(err);
352
353 alg = crypto_get_attr_alg(tb, CRYPTO_ALG_TYPE_CIPHER,
354 CRYPTO_ALG_TYPE_MASK);
355 if (IS_ERR(alg))
356 return ERR_CAST(alg);
357
358 inst = ERR_PTR(-EINVAL);
359 /* Section 5.1 requirement for KW */
360 if (alg->cra_blocksize != sizeof(struct crypto_kw_block))
361 goto err;
362
363 inst = crypto_alloc_instance("kw", alg);
364 if (IS_ERR(inst))
365 goto err;
366
367 inst->alg.cra_flags = CRYPTO_ALG_TYPE_BLKCIPHER;
368 inst->alg.cra_priority = alg->cra_priority;
369 inst->alg.cra_blocksize = SEMIBSIZE;
370 inst->alg.cra_alignmask = 0;
371 inst->alg.cra_type = &crypto_blkcipher_type;
372 inst->alg.cra_blkcipher.ivsize = SEMIBSIZE;
373 inst->alg.cra_blkcipher.min_keysize = alg->cra_cipher.cia_min_keysize;
374 inst->alg.cra_blkcipher.max_keysize = alg->cra_cipher.cia_max_keysize;
375
376 inst->alg.cra_ctxsize = sizeof(struct crypto_kw_ctx);
377
378 inst->alg.cra_init = crypto_kw_init_tfm;
379 inst->alg.cra_exit = crypto_kw_exit_tfm;
380
381 inst->alg.cra_blkcipher.setkey = crypto_kw_setkey;
382 inst->alg.cra_blkcipher.encrypt = crypto_kw_encrypt;
383 inst->alg.cra_blkcipher.decrypt = crypto_kw_decrypt;
384
385err:
386 crypto_mod_put(alg);
387 return inst;
388}
389
390static void crypto_kw_free(struct crypto_instance *inst)
391{
392 crypto_drop_spawn(crypto_instance_ctx(inst));
393 kfree(inst);
394}
395
396static struct crypto_template crypto_kw_tmpl = {
397 .name = "kw",
398 .alloc = crypto_kw_alloc,
399 .free = crypto_kw_free,
400 .module = THIS_MODULE,
401};
402
403static int __init crypto_kw_init(void)
404{
405 return crypto_register_template(&crypto_kw_tmpl);
406}
407
408static void __exit crypto_kw_exit(void)
409{
410 crypto_unregister_template(&crypto_kw_tmpl);
411}
412
413module_init(crypto_kw_init);
414module_exit(crypto_kw_exit);
415
416MODULE_LICENSE("Dual BSD/GPL");
417MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");
418MODULE_DESCRIPTION("Key Wrapping (RFC3394 / NIST SP800-38F)");
419MODULE_ALIAS_CRYPTO("kw");