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