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, pt, 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, ct, ctlen);
74 *	skcipher_request_set_crypt(req, &sg, &sg, ctlen, 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/cipher.h>
89#include <crypto/internal/skcipher.h>
90
91struct crypto_kw_block {
92#define SEMIBSIZE 8
93	__be64 A;
94	__be64 R;
95};
96
97/*
98 * Fast forward the SGL to the "end" length minus SEMIBSIZE.
99 * The start in the SGL defined by the fast-forward is returned with
100 * the walk variable
101 */
102static void crypto_kw_scatterlist_ff(struct scatter_walk *walk,
103				     struct scatterlist *sg,
104				     unsigned int end)
105{
106	unsigned int skip = 0;
107
108	/* The caller should only operate on full SEMIBLOCKs. */
109	BUG_ON(end < SEMIBSIZE);
110
111	skip = end - SEMIBSIZE;
112	while (sg) {
113		if (sg->length > skip) {
114			scatterwalk_start(walk, sg);
115			scatterwalk_advance(walk, skip);
116			break;
117		}
118
119		skip -= sg->length;
120		sg = sg_next(sg);
121	}
122}
123
124static int crypto_kw_decrypt(struct skcipher_request *req)
125{
126	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
127	struct crypto_cipher *cipher = skcipher_cipher_simple(tfm);
128	struct crypto_kw_block block;
129	struct scatterlist *src, *dst;
130	u64 t = 6 * ((req->cryptlen) >> 3);
131	unsigned int i;
132	int ret = 0;
133
134	/*
135	 * Require at least 2 semiblocks (note, the 3rd semiblock that is
136	 * required by SP800-38F is the IV.
137	 */
138	if (req->cryptlen < (2 * SEMIBSIZE) || req->cryptlen % SEMIBSIZE)
139		return -EINVAL;
140
141	/* Place the IV into block A */
142	memcpy(&block.A, req->iv, SEMIBSIZE);
143
144	/*
145	 * src scatterlist is read-only. dst scatterlist is r/w. During the
146	 * first loop, src points to req->src and dst to req->dst. For any
147	 * subsequent round, the code operates on req->dst only.
148	 */
149	src = req->src;
150	dst = req->dst;
151
152	for (i = 0; i < 6; i++) {
153		struct scatter_walk src_walk, dst_walk;
154		unsigned int nbytes = req->cryptlen;
155
156		while (nbytes) {
157			/* move pointer by nbytes in the SGL */
158			crypto_kw_scatterlist_ff(&src_walk, src, nbytes);
159			/* get the source block */
160			scatterwalk_copychunks(&block.R, &src_walk, SEMIBSIZE,
161					       false);
162
163			/* perform KW operation: modify IV with counter */
164			block.A ^= cpu_to_be64(t);
165			t--;
166			/* perform KW operation: decrypt block */
167			crypto_cipher_decrypt_one(cipher, (u8 *)&block,
168						  (u8 *)&block);
169
170			/* move pointer by nbytes in the SGL */
171			crypto_kw_scatterlist_ff(&dst_walk, dst, nbytes);
172			/* Copy block->R into place */
173			scatterwalk_copychunks(&block.R, &dst_walk, SEMIBSIZE,
174					       true);
175
176			nbytes -= SEMIBSIZE;
177		}
178
179		/* we now start to operate on the dst SGL only */
180		src = req->dst;
181		dst = req->dst;
182	}
183
184	/* Perform authentication check */
185	if (block.A != cpu_to_be64(0xa6a6a6a6a6a6a6a6ULL))
186		ret = -EBADMSG;
187
188	memzero_explicit(&block, sizeof(struct crypto_kw_block));
189
190	return ret;
191}
192
193static int crypto_kw_encrypt(struct skcipher_request *req)
194{
195	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
196	struct crypto_cipher *cipher = skcipher_cipher_simple(tfm);
197	struct crypto_kw_block block;
198	struct scatterlist *src, *dst;
199	u64 t = 1;
200	unsigned int i;
201
202	/*
203	 * Require at least 2 semiblocks (note, the 3rd semiblock that is
204	 * required by SP800-38F is the IV that occupies the first semiblock.
205	 * This means that the dst memory must be one semiblock larger than src.
206	 * Also ensure that the given data is aligned to semiblock.
207	 */
208	if (req->cryptlen < (2 * SEMIBSIZE) || req->cryptlen % SEMIBSIZE)
209		return -EINVAL;
210
211	/*
212	 * Place the predefined IV into block A -- for encrypt, the caller
213	 * does not need to provide an IV, but he needs to fetch the final IV.
214	 */
215	block.A = cpu_to_be64(0xa6a6a6a6a6a6a6a6ULL);
216
217	/*
218	 * src scatterlist is read-only. dst scatterlist is r/w. During the
219	 * first loop, src points to req->src and dst to req->dst. For any
220	 * subsequent round, the code operates on req->dst only.
221	 */
222	src = req->src;
223	dst = req->dst;
224
225	for (i = 0; i < 6; i++) {
226		struct scatter_walk src_walk, dst_walk;
227		unsigned int nbytes = req->cryptlen;
228
229		scatterwalk_start(&src_walk, src);
230		scatterwalk_start(&dst_walk, dst);
231
232		while (nbytes) {
233			/* get the source block */
234			scatterwalk_copychunks(&block.R, &src_walk, SEMIBSIZE,
235					       false);
236
237			/* perform KW operation: encrypt block */
238			crypto_cipher_encrypt_one(cipher, (u8 *)&block,
239						  (u8 *)&block);
240			/* perform KW operation: modify IV with counter */
241			block.A ^= cpu_to_be64(t);
242			t++;
243
244			/* Copy block->R into place */
245			scatterwalk_copychunks(&block.R, &dst_walk, SEMIBSIZE,
246					       true);
247
248			nbytes -= SEMIBSIZE;
249		}
250
251		/* we now start to operate on the dst SGL only */
252		src = req->dst;
253		dst = req->dst;
254	}
255
256	/* establish the IV for the caller to pick up */
257	memcpy(req->iv, &block.A, SEMIBSIZE);
258
259	memzero_explicit(&block, sizeof(struct crypto_kw_block));
260
261	return 0;
262}
263
264static int crypto_kw_create(struct crypto_template *tmpl, struct rtattr **tb)
265{
266	struct skcipher_instance *inst;
267	struct crypto_alg *alg;
268	int err;
269
270	inst = skcipher_alloc_instance_simple(tmpl, tb);
271	if (IS_ERR(inst))
272		return PTR_ERR(inst);
273
274	alg = skcipher_ialg_simple(inst);
275
276	err = -EINVAL;
277	/* Section 5.1 requirement for KW */
278	if (alg->cra_blocksize != sizeof(struct crypto_kw_block))
279		goto out_free_inst;
280
281	inst->alg.base.cra_blocksize = SEMIBSIZE;
282	inst->alg.base.cra_alignmask = 0;
283	inst->alg.ivsize = SEMIBSIZE;
284
285	inst->alg.encrypt = crypto_kw_encrypt;
286	inst->alg.decrypt = crypto_kw_decrypt;
287
288	err = skcipher_register_instance(tmpl, inst);
289	if (err) {
290out_free_inst:
291		inst->free(inst);
292	}
293
294	return err;
295}
296
297static struct crypto_template crypto_kw_tmpl = {
298	.name = "kw",
299	.create = crypto_kw_create,
300	.module = THIS_MODULE,
301};
302
303static int __init crypto_kw_init(void)
304{
305	return crypto_register_template(&crypto_kw_tmpl);
306}
307
308static void __exit crypto_kw_exit(void)
309{
310	crypto_unregister_template(&crypto_kw_tmpl);
311}
312
313subsys_initcall(crypto_kw_init);
314module_exit(crypto_kw_exit);
315
316MODULE_LICENSE("Dual BSD/GPL");
317MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");
318MODULE_DESCRIPTION("Key Wrapping (RFC3394 / NIST SP800-38F)");
319MODULE_ALIAS_CRYPTO("kw");
320MODULE_IMPORT_NS(CRYPTO_INTERNAL);
321