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Linux/crypto/keywrap.c

  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         u8 A[SEMIBSIZE];
 97         u8 R[SEMIBSIZE];
 98 };
 99 
100 /* convert 64 bit integer into its string representation */
101 static 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  */
113 static 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 
135 static 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 
220 static 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 
305 static 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 
321 static 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 
336 static 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 
343 static 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 
385 err:
386         crypto_mod_put(alg);
387         return inst;
388 }
389 
390 static void crypto_kw_free(struct crypto_instance *inst)
391 {
392         crypto_drop_spawn(crypto_instance_ctx(inst));
393         kfree(inst);
394 }
395 
396 static 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 
403 static int __init crypto_kw_init(void)
404 {
405         return crypto_register_template(&crypto_kw_tmpl);
406 }
407 
408 static void __exit crypto_kw_exit(void)
409 {
410         crypto_unregister_template(&crypto_kw_tmpl);
411 }
412 
413 module_init(crypto_kw_init);
414 module_exit(crypto_kw_exit);
415 
416 MODULE_LICENSE("Dual BSD/GPL");
417 MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");
418 MODULE_DESCRIPTION("Key Wrapping (RFC3394 / NIST SP800-38F)");
419 MODULE_ALIAS_CRYPTO("kw");
420 

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