aboutsummaryrefslogtreecommitdiff
path: root/crypto/keywrap.c
blob: a155c88105ea1a91fb9d4f4fde2cf22ec8e1713f (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
/*
 * Key Wrapping: RFC3394 / NIST SP800-38F
 *
 * Copyright (C) 2015, Stephan Mueller <smueller@chronox.de>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, and the entire permission notice in its entirety,
 *    including the disclaimer of warranties.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote
 *    products derived from this software without specific prior
 *    written permission.
 *
 * ALTERNATIVELY, this product may be distributed under the terms of
 * the GNU General Public License, in which case the provisions of the GPL2
 * are required INSTEAD OF the above restrictions.  (This clause is
 * necessary due to a potential bad interaction between the GPL and
 * the restrictions contained in a BSD-style copyright.)
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF
 * WHICH ARE HEREBY DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
 * USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH
 * DAMAGE.
 */

/*
 * Note for using key wrapping:
 *
 *	* The result of the encryption operation is the ciphertext starting
 *	  with the 2nd semiblock. The first semiblock is provided as the IV.
 *	  The IV used to start the encryption operation is the default IV.
 *
 *	* The input for the decryption is the first semiblock handed in as an
 *	  IV. The ciphertext is the data starting with the 2nd semiblock. The
 *	  return code of the decryption operation will be EBADMSG in case an
 *	  integrity error occurs.
 *
 * To obtain the full result of an encryption as expected by SP800-38F, the
 * caller must allocate a buffer of plaintext + 8 bytes:
 *
 *	unsigned int datalen = ptlen + crypto_skcipher_ivsize(tfm);
 *	u8 data[datalen];
 *	u8 *iv = data;
 *	u8 *pt = data + crypto_skcipher_ivsize(tfm);
 *		<ensure that pt contains the plaintext of size ptlen>
 *	sg_init_one(&sg, pt, ptlen);
 *	skcipher_request_set_crypt(req, &sg, &sg, ptlen, iv);
 *
 *	==> After encryption, data now contains full KW result as per SP800-38F.
 *
 * In case of decryption, ciphertext now already has the expected length
 * and must be segmented appropriately:
 *
 *	unsigned int datalen = CTLEN;
 *	u8 data[datalen];
 *		<ensure that data contains full ciphertext>
 *	u8 *iv = data;
 *	u8 *ct = data + crypto_skcipher_ivsize(tfm);
 *	unsigned int ctlen = datalen - crypto_skcipher_ivsize(tfm);
 *	sg_init_one(&sg, ct, ctlen);
 *	skcipher_request_set_crypt(req, &sg, &sg, ctlen, iv);
 *
 *	==> After decryption (which hopefully does not return EBADMSG), the ct
 *	pointer now points to the plaintext of size ctlen.
 *
 * Note 2: KWP is not implemented as this would defy in-place operation.
 *	   If somebody wants to wrap non-aligned data, he should simply pad
 *	   the input with zeros to fill it up to the 8 byte boundary.
 */

#include <linux/module.h>
#include <linux/crypto.h>
#include <linux/scatterlist.h>
#include <crypto/scatterwalk.h>
#include <crypto/internal/skcipher.h>

struct crypto_kw_block {
#define SEMIBSIZE 8
	__be64 A;
	__be64 R;
};

/*
 * Fast forward the SGL to the "end" length minus SEMIBSIZE.
 * The start in the SGL defined by the fast-forward is returned with
 * the walk variable
 */
static void crypto_kw_scatterlist_ff(struct scatter_walk *walk,
				     struct scatterlist *sg,
				     unsigned int end)
{
	unsigned int skip = 0;

	/* The caller should only operate on full SEMIBLOCKs. */
	BUG_ON(end < SEMIBSIZE);

	skip = end - SEMIBSIZE;
	while (sg) {
		if (sg->length > skip) {
			scatterwalk_start(walk, sg);
			scatterwalk_advance(walk, skip);
			break;
		} else
			skip -= sg->length;

		sg = sg_next(sg);
	}
}

static int crypto_kw_decrypt(struct skcipher_request *req)
{
	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
	struct crypto_cipher *cipher = skcipher_cipher_simple(tfm);
	struct crypto_kw_block block;
	struct scatterlist *src, *dst;
	u64 t = 6 * ((req->cryptlen) >> 3);
	unsigned int i;
	int ret = 0;

	/*
	 * Require at least 2 semiblocks (note, the 3rd semiblock that is
	 * required by SP800-38F is the IV.
	 */
	if (req->cryptlen < (2 * SEMIBSIZE) || req->cryptlen % SEMIBSIZE)
		return -EINVAL;

	/* Place the IV into block A */
	memcpy(&block.A, req->iv, SEMIBSIZE);

	/*
	 * src scatterlist is read-only. dst scatterlist is r/w. During the
	 * first loop, src points to req->src and dst to req->dst. For any
	 * subsequent round, the code operates on req->dst only.
	 */
	src = req->src;
	dst = req->dst;

	for (i = 0; i < 6; i++) {
		struct scatter_walk src_walk, dst_walk;
		unsigned int nbytes = req->cryptlen;

		while (nbytes) {
			/* move pointer by nbytes in the SGL */
			crypto_kw_scatterlist_ff(&src_walk, src, nbytes);
			/* get the source block */
			scatterwalk_copychunks(&block.R, &src_walk, SEMIBSIZE,
					       false);

			/* perform KW operation: modify IV with counter */
			block.A ^= cpu_to_be64(t);
			t--;
			/* perform KW operation: decrypt block */
			crypto_cipher_decrypt_one(cipher, (u8 *)&block,
						  (u8 *)&block);

			/* move pointer by nbytes in the SGL */
			crypto_kw_scatterlist_ff(&dst_walk, dst, nbytes);
			/* Copy block->R into place */
			scatterwalk_copychunks(&block.R, &dst_walk, SEMIBSIZE,
					       true);

			nbytes -= SEMIBSIZE;
		}

		/* we now start to operate on the dst SGL only */
		src = req->dst;
		dst = req->dst;
	}

	/* Perform authentication check */
	if (block.A != cpu_to_be64(0xa6a6a6a6a6a6a6a6ULL))
		ret = -EBADMSG;

	memzero_explicit(&block, sizeof(struct crypto_kw_block));

	return ret;
}

static int crypto_kw_encrypt(struct skcipher_request *req)
{
	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
	struct crypto_cipher *cipher = skcipher_cipher_simple(tfm);
	struct crypto_kw_block block;
	struct scatterlist *src, *dst;
	u64 t = 1;
	unsigned int i;

	/*
	 * Require at least 2 semiblocks (note, the 3rd semiblock that is
	 * required by SP800-38F is the IV that occupies the first semiblock.
	 * This means that the dst memory must be one semiblock larger than src.
	 * Also ensure that the given data is aligned to semiblock.
	 */
	if (req->cryptlen < (2 * SEMIBSIZE) || req->cryptlen % SEMIBSIZE)
		return -EINVAL;

	/*
	 * Place the predefined IV into block A -- for encrypt, the caller
	 * does not need to provide an IV, but he needs to fetch the final IV.
	 */
	block.A = cpu_to_be64(0xa6a6a6a6a6a6a6a6ULL);

	/*
	 * src scatterlist is read-only. dst scatterlist is r/w. During the
	 * first loop, src points to req->src and dst to req->dst. For any
	 * subsequent round, the code operates on req->dst only.
	 */
	src = req->src;
	dst = req->dst;

	for (i = 0; i < 6; i++) {
		struct scatter_walk src_walk, dst_walk;
		unsigned int nbytes = req->cryptlen;

		scatterwalk_start(&src_walk, src);
		scatterwalk_start(&dst_walk, dst);

		while (nbytes) {
			/* get the source block */
			scatterwalk_copychunks(&block.R, &src_walk, SEMIBSIZE,
					       false);

			/* perform KW operation: encrypt block */
			crypto_cipher_encrypt_one(cipher, (u8 *)&block,
						  (u8 *)&block);
			/* perform KW operation: modify IV with counter */
			block.A ^= cpu_to_be64(t);
			t++;

			/* Copy block->R into place */
			scatterwalk_copychunks(&block.R, &dst_walk, SEMIBSIZE,
					       true);

			nbytes -= SEMIBSIZE;
		}

		/* we now start to operate on the dst SGL only */
		src = req->dst;
		dst = req->dst;
	}

	/* establish the IV for the caller to pick up */
	memcpy(req->iv, &block.A, SEMIBSIZE);

	memzero_explicit(&block, sizeof(struct crypto_kw_block));

	return 0;
}

static int crypto_kw_create(struct crypto_template *tmpl, struct rtattr **tb)
{
	struct skcipher_instance *inst;
	struct crypto_alg *alg;
	int err;

	inst = skcipher_alloc_instance_simple(tmpl, tb, &alg);
	if (IS_ERR(inst))
		return PTR_ERR(inst);

	err = -EINVAL;
	/* Section 5.1 requirement for KW */
	if (alg->cra_blocksize != sizeof(struct crypto_kw_block))
		goto out_free_inst;

	inst->alg.base.cra_blocksize = SEMIBSIZE;
	inst->alg.base.cra_alignmask = 0;
	inst->alg.ivsize = SEMIBSIZE;

	inst->alg.encrypt = crypto_kw_encrypt;
	inst->alg.decrypt = crypto_kw_decrypt;

	err = skcipher_register_instance(tmpl, inst);
	if (err)
		goto out_free_inst;
	goto out_put_alg;

out_free_inst:
	inst->free(inst);
out_put_alg:
	crypto_mod_put(alg);
	return err;
}

static struct crypto_template crypto_kw_tmpl = {
	.name = "kw",
	.create = crypto_kw_create,
	.module = THIS_MODULE,
};

static int __init crypto_kw_init(void)
{
	return crypto_register_template(&crypto_kw_tmpl);
}

static void __exit crypto_kw_exit(void)
{
	crypto_unregister_template(&crypto_kw_tmpl);
}

subsys_initcall(crypto_kw_init);
module_exit(crypto_kw_exit);

MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");
MODULE_DESCRIPTION("Key Wrapping (RFC3394 / NIST SP800-38F)");
MODULE_ALIAS_CRYPTO("kw");