xref: /linux/crypto/xts.c (revision 827634added7f38b7d724cab1dccdb2b004c13c3)
1 /* XTS: as defined in IEEE1619/D16
2  *	http://grouper.ieee.org/groups/1619/email/pdf00086.pdf
3  *	(sector sizes which are not a multiple of 16 bytes are,
4  *	however currently unsupported)
5  *
6  * Copyright (c) 2007 Rik Snel <rsnel@cube.dyndns.org>
7  *
8  * Based om ecb.c
9  * Copyright (c) 2006 Herbert Xu <herbert@gondor.apana.org.au>
10  *
11  * This program is free software; you can redistribute it and/or modify it
12  * under the terms of the GNU General Public License as published by the Free
13  * Software Foundation; either version 2 of the License, or (at your option)
14  * any later version.
15  */
16 #include <crypto/algapi.h>
17 #include <linux/err.h>
18 #include <linux/init.h>
19 #include <linux/kernel.h>
20 #include <linux/module.h>
21 #include <linux/scatterlist.h>
22 #include <linux/slab.h>
23 
24 #include <crypto/xts.h>
25 #include <crypto/b128ops.h>
26 #include <crypto/gf128mul.h>
27 
28 struct priv {
29 	struct crypto_cipher *child;
30 	struct crypto_cipher *tweak;
31 };
32 
33 static int setkey(struct crypto_tfm *parent, const u8 *key,
34 		  unsigned int keylen)
35 {
36 	struct priv *ctx = crypto_tfm_ctx(parent);
37 	struct crypto_cipher *child = ctx->tweak;
38 	u32 *flags = &parent->crt_flags;
39 	int err;
40 
41 	/* key consists of keys of equal size concatenated, therefore
42 	 * the length must be even */
43 	if (keylen % 2) {
44 		/* tell the user why there was an error */
45 		*flags |= CRYPTO_TFM_RES_BAD_KEY_LEN;
46 		return -EINVAL;
47 	}
48 
49 	/* we need two cipher instances: one to compute the initial 'tweak'
50 	 * by encrypting the IV (usually the 'plain' iv) and the other
51 	 * one to encrypt and decrypt the data */
52 
53 	/* tweak cipher, uses Key2 i.e. the second half of *key */
54 	crypto_cipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
55 	crypto_cipher_set_flags(child, crypto_tfm_get_flags(parent) &
56 				       CRYPTO_TFM_REQ_MASK);
57 	err = crypto_cipher_setkey(child, key + keylen/2, keylen/2);
58 	if (err)
59 		return err;
60 
61 	crypto_tfm_set_flags(parent, crypto_cipher_get_flags(child) &
62 				     CRYPTO_TFM_RES_MASK);
63 
64 	child = ctx->child;
65 
66 	/* data cipher, uses Key1 i.e. the first half of *key */
67 	crypto_cipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
68 	crypto_cipher_set_flags(child, crypto_tfm_get_flags(parent) &
69 				       CRYPTO_TFM_REQ_MASK);
70 	err = crypto_cipher_setkey(child, key, keylen/2);
71 	if (err)
72 		return err;
73 
74 	crypto_tfm_set_flags(parent, crypto_cipher_get_flags(child) &
75 				     CRYPTO_TFM_RES_MASK);
76 
77 	return 0;
78 }
79 
80 struct sinfo {
81 	be128 *t;
82 	struct crypto_tfm *tfm;
83 	void (*fn)(struct crypto_tfm *, u8 *, const u8 *);
84 };
85 
86 static inline void xts_round(struct sinfo *s, void *dst, const void *src)
87 {
88 	be128_xor(dst, s->t, src);		/* PP <- T xor P */
89 	s->fn(s->tfm, dst, dst);		/* CC <- E(Key1,PP) */
90 	be128_xor(dst, dst, s->t);		/* C <- T xor CC */
91 }
92 
93 static int crypt(struct blkcipher_desc *d,
94 		 struct blkcipher_walk *w, struct priv *ctx,
95 		 void (*tw)(struct crypto_tfm *, u8 *, const u8 *),
96 		 void (*fn)(struct crypto_tfm *, u8 *, const u8 *))
97 {
98 	int err;
99 	unsigned int avail;
100 	const int bs = XTS_BLOCK_SIZE;
101 	struct sinfo s = {
102 		.tfm = crypto_cipher_tfm(ctx->child),
103 		.fn = fn
104 	};
105 	u8 *wsrc;
106 	u8 *wdst;
107 
108 	err = blkcipher_walk_virt(d, w);
109 	if (!w->nbytes)
110 		return err;
111 
112 	s.t = (be128 *)w->iv;
113 	avail = w->nbytes;
114 
115 	wsrc = w->src.virt.addr;
116 	wdst = w->dst.virt.addr;
117 
118 	/* calculate first value of T */
119 	tw(crypto_cipher_tfm(ctx->tweak), w->iv, w->iv);
120 
121 	goto first;
122 
123 	for (;;) {
124 		do {
125 			gf128mul_x_ble(s.t, s.t);
126 
127 first:
128 			xts_round(&s, wdst, wsrc);
129 
130 			wsrc += bs;
131 			wdst += bs;
132 		} while ((avail -= bs) >= bs);
133 
134 		err = blkcipher_walk_done(d, w, avail);
135 		if (!w->nbytes)
136 			break;
137 
138 		avail = w->nbytes;
139 
140 		wsrc = w->src.virt.addr;
141 		wdst = w->dst.virt.addr;
142 	}
143 
144 	return err;
145 }
146 
147 static int encrypt(struct blkcipher_desc *desc, struct scatterlist *dst,
148 		   struct scatterlist *src, unsigned int nbytes)
149 {
150 	struct priv *ctx = crypto_blkcipher_ctx(desc->tfm);
151 	struct blkcipher_walk w;
152 
153 	blkcipher_walk_init(&w, dst, src, nbytes);
154 	return crypt(desc, &w, ctx, crypto_cipher_alg(ctx->tweak)->cia_encrypt,
155 		     crypto_cipher_alg(ctx->child)->cia_encrypt);
156 }
157 
158 static int decrypt(struct blkcipher_desc *desc, struct scatterlist *dst,
159 		   struct scatterlist *src, unsigned int nbytes)
160 {
161 	struct priv *ctx = crypto_blkcipher_ctx(desc->tfm);
162 	struct blkcipher_walk w;
163 
164 	blkcipher_walk_init(&w, dst, src, nbytes);
165 	return crypt(desc, &w, ctx, crypto_cipher_alg(ctx->tweak)->cia_encrypt,
166 		     crypto_cipher_alg(ctx->child)->cia_decrypt);
167 }
168 
169 int xts_crypt(struct blkcipher_desc *desc, struct scatterlist *sdst,
170 	      struct scatterlist *ssrc, unsigned int nbytes,
171 	      struct xts_crypt_req *req)
172 {
173 	const unsigned int bsize = XTS_BLOCK_SIZE;
174 	const unsigned int max_blks = req->tbuflen / bsize;
175 	struct blkcipher_walk walk;
176 	unsigned int nblocks;
177 	be128 *src, *dst, *t;
178 	be128 *t_buf = req->tbuf;
179 	int err, i;
180 
181 	BUG_ON(max_blks < 1);
182 
183 	blkcipher_walk_init(&walk, sdst, ssrc, nbytes);
184 
185 	err = blkcipher_walk_virt(desc, &walk);
186 	nbytes = walk.nbytes;
187 	if (!nbytes)
188 		return err;
189 
190 	nblocks = min(nbytes / bsize, max_blks);
191 	src = (be128 *)walk.src.virt.addr;
192 	dst = (be128 *)walk.dst.virt.addr;
193 
194 	/* calculate first value of T */
195 	req->tweak_fn(req->tweak_ctx, (u8 *)&t_buf[0], walk.iv);
196 
197 	i = 0;
198 	goto first;
199 
200 	for (;;) {
201 		do {
202 			for (i = 0; i < nblocks; i++) {
203 				gf128mul_x_ble(&t_buf[i], t);
204 first:
205 				t = &t_buf[i];
206 
207 				/* PP <- T xor P */
208 				be128_xor(dst + i, t, src + i);
209 			}
210 
211 			/* CC <- E(Key2,PP) */
212 			req->crypt_fn(req->crypt_ctx, (u8 *)dst,
213 				      nblocks * bsize);
214 
215 			/* C <- T xor CC */
216 			for (i = 0; i < nblocks; i++)
217 				be128_xor(dst + i, dst + i, &t_buf[i]);
218 
219 			src += nblocks;
220 			dst += nblocks;
221 			nbytes -= nblocks * bsize;
222 			nblocks = min(nbytes / bsize, max_blks);
223 		} while (nblocks > 0);
224 
225 		*(be128 *)walk.iv = *t;
226 
227 		err = blkcipher_walk_done(desc, &walk, nbytes);
228 		nbytes = walk.nbytes;
229 		if (!nbytes)
230 			break;
231 
232 		nblocks = min(nbytes / bsize, max_blks);
233 		src = (be128 *)walk.src.virt.addr;
234 		dst = (be128 *)walk.dst.virt.addr;
235 	}
236 
237 	return err;
238 }
239 EXPORT_SYMBOL_GPL(xts_crypt);
240 
241 static int init_tfm(struct crypto_tfm *tfm)
242 {
243 	struct crypto_cipher *cipher;
244 	struct crypto_instance *inst = (void *)tfm->__crt_alg;
245 	struct crypto_spawn *spawn = crypto_instance_ctx(inst);
246 	struct priv *ctx = crypto_tfm_ctx(tfm);
247 	u32 *flags = &tfm->crt_flags;
248 
249 	cipher = crypto_spawn_cipher(spawn);
250 	if (IS_ERR(cipher))
251 		return PTR_ERR(cipher);
252 
253 	if (crypto_cipher_blocksize(cipher) != XTS_BLOCK_SIZE) {
254 		*flags |= CRYPTO_TFM_RES_BAD_BLOCK_LEN;
255 		crypto_free_cipher(cipher);
256 		return -EINVAL;
257 	}
258 
259 	ctx->child = cipher;
260 
261 	cipher = crypto_spawn_cipher(spawn);
262 	if (IS_ERR(cipher)) {
263 		crypto_free_cipher(ctx->child);
264 		return PTR_ERR(cipher);
265 	}
266 
267 	/* this check isn't really needed, leave it here just in case */
268 	if (crypto_cipher_blocksize(cipher) != XTS_BLOCK_SIZE) {
269 		crypto_free_cipher(cipher);
270 		crypto_free_cipher(ctx->child);
271 		*flags |= CRYPTO_TFM_RES_BAD_BLOCK_LEN;
272 		return -EINVAL;
273 	}
274 
275 	ctx->tweak = cipher;
276 
277 	return 0;
278 }
279 
280 static void exit_tfm(struct crypto_tfm *tfm)
281 {
282 	struct priv *ctx = crypto_tfm_ctx(tfm);
283 	crypto_free_cipher(ctx->child);
284 	crypto_free_cipher(ctx->tweak);
285 }
286 
287 static struct crypto_instance *alloc(struct rtattr **tb)
288 {
289 	struct crypto_instance *inst;
290 	struct crypto_alg *alg;
291 	int err;
292 
293 	err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_BLKCIPHER);
294 	if (err)
295 		return ERR_PTR(err);
296 
297 	alg = crypto_get_attr_alg(tb, CRYPTO_ALG_TYPE_CIPHER,
298 				  CRYPTO_ALG_TYPE_MASK);
299 	if (IS_ERR(alg))
300 		return ERR_CAST(alg);
301 
302 	inst = crypto_alloc_instance("xts", alg);
303 	if (IS_ERR(inst))
304 		goto out_put_alg;
305 
306 	inst->alg.cra_flags = CRYPTO_ALG_TYPE_BLKCIPHER;
307 	inst->alg.cra_priority = alg->cra_priority;
308 	inst->alg.cra_blocksize = alg->cra_blocksize;
309 
310 	if (alg->cra_alignmask < 7)
311 		inst->alg.cra_alignmask = 7;
312 	else
313 		inst->alg.cra_alignmask = alg->cra_alignmask;
314 
315 	inst->alg.cra_type = &crypto_blkcipher_type;
316 
317 	inst->alg.cra_blkcipher.ivsize = alg->cra_blocksize;
318 	inst->alg.cra_blkcipher.min_keysize =
319 		2 * alg->cra_cipher.cia_min_keysize;
320 	inst->alg.cra_blkcipher.max_keysize =
321 		2 * alg->cra_cipher.cia_max_keysize;
322 
323 	inst->alg.cra_ctxsize = sizeof(struct priv);
324 
325 	inst->alg.cra_init = init_tfm;
326 	inst->alg.cra_exit = exit_tfm;
327 
328 	inst->alg.cra_blkcipher.setkey = setkey;
329 	inst->alg.cra_blkcipher.encrypt = encrypt;
330 	inst->alg.cra_blkcipher.decrypt = decrypt;
331 
332 out_put_alg:
333 	crypto_mod_put(alg);
334 	return inst;
335 }
336 
337 static void free(struct crypto_instance *inst)
338 {
339 	crypto_drop_spawn(crypto_instance_ctx(inst));
340 	kfree(inst);
341 }
342 
343 static struct crypto_template crypto_tmpl = {
344 	.name = "xts",
345 	.alloc = alloc,
346 	.free = free,
347 	.module = THIS_MODULE,
348 };
349 
350 static int __init crypto_module_init(void)
351 {
352 	return crypto_register_template(&crypto_tmpl);
353 }
354 
355 static void __exit crypto_module_exit(void)
356 {
357 	crypto_unregister_template(&crypto_tmpl);
358 }
359 
360 module_init(crypto_module_init);
361 module_exit(crypto_module_exit);
362 
363 MODULE_LICENSE("GPL");
364 MODULE_DESCRIPTION("XTS block cipher mode");
365 MODULE_ALIAS_CRYPTO("xts");
366