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/b128ops.h>
25#include <crypto/gf128mul.h>
26
27struct priv {
28	struct crypto_cipher *child;
29	struct crypto_cipher *tweak;
30};
31
32static int setkey(struct crypto_tfm *parent, const u8 *key,
33		  unsigned int keylen)
34{
35	struct priv *ctx = crypto_tfm_ctx(parent);
36	struct crypto_cipher *child = ctx->tweak;
37	u32 *flags = &parent->crt_flags;
38	int err;
39
40	/* key consists of keys of equal size concatenated, therefore
41	 * the length must be even */
42	if (keylen % 2) {
43		/* tell the user why there was an error */
44		*flags |= CRYPTO_TFM_RES_BAD_KEY_LEN;
45		return -EINVAL;
46	}
47
48	/* we need two cipher instances: one to compute the inital 'tweak'
49	 * by encrypting the IV (usually the 'plain' iv) and the other
50	 * one to encrypt and decrypt the data */
51
52	/* tweak cipher, uses Key2 i.e. the second half of *key */
53	crypto_cipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
54	crypto_cipher_set_flags(child, crypto_tfm_get_flags(parent) &
55				       CRYPTO_TFM_REQ_MASK);
56	err = crypto_cipher_setkey(child, key + keylen/2, keylen/2);
57	if (err)
58		return err;
59
60	crypto_tfm_set_flags(parent, crypto_cipher_get_flags(child) &
61				     CRYPTO_TFM_RES_MASK);
62
63	child = ctx->child;
64
65	/* data cipher, uses Key1 i.e. the first half of *key */
66	crypto_cipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
67	crypto_cipher_set_flags(child, crypto_tfm_get_flags(parent) &
68				       CRYPTO_TFM_REQ_MASK);
69	err = crypto_cipher_setkey(child, key, keylen/2);
70	if (err)
71		return err;
72
73	crypto_tfm_set_flags(parent, crypto_cipher_get_flags(child) &
74				     CRYPTO_TFM_RES_MASK);
75
76	return 0;
77}
78
79struct sinfo {
80	be128 *t;
81	struct crypto_tfm *tfm;
82	void (*fn)(struct crypto_tfm *, u8 *, const u8 *);
83};
84
85static inline void xts_round(struct sinfo *s, void *dst, const void *src)
86{
87	be128_xor(dst, s->t, src);		/* PP <- T xor P */
88	s->fn(s->tfm, dst, dst);		/* CC <- E(Key1,PP) */
89	be128_xor(dst, dst, s->t);		/* C <- T xor CC */
90}
91
92static int crypt(struct blkcipher_desc *d,
93		 struct blkcipher_walk *w, struct priv *ctx,
94		 void (*tw)(struct crypto_tfm *, u8 *, const u8 *),
95		 void (*fn)(struct crypto_tfm *, u8 *, const u8 *))
96{
97	int err;
98	unsigned int avail;
99	const int bs = crypto_cipher_blocksize(ctx->child);
100	struct sinfo s = {
101		.tfm = crypto_cipher_tfm(ctx->child),
102		.fn = fn
103	};
104	u8 *wsrc;
105	u8 *wdst;
106
107	err = blkcipher_walk_virt(d, w);
108	if (!w->nbytes)
109		return err;
110
111	s.t = (be128 *)w->iv;
112	avail = w->nbytes;
113
114	wsrc = w->src.virt.addr;
115	wdst = w->dst.virt.addr;
116
117	/* calculate first value of T */
118	tw(crypto_cipher_tfm(ctx->tweak), w->iv, w->iv);
119
120	goto first;
121
122	for (;;) {
123		do {
124			gf128mul_x_ble(s.t, s.t);
125
126first:
127			xts_round(&s, wdst, wsrc);
128
129			wsrc += bs;
130			wdst += bs;
131		} while ((avail -= bs) >= bs);
132
133		err = blkcipher_walk_done(d, w, avail);
134		if (!w->nbytes)
135			break;
136
137		avail = w->nbytes;
138
139		wsrc = w->src.virt.addr;
140		wdst = w->dst.virt.addr;
141	}
142
143	return err;
144}
145
146static int encrypt(struct blkcipher_desc *desc, struct scatterlist *dst,
147		   struct scatterlist *src, unsigned int nbytes)
148{
149	struct priv *ctx = crypto_blkcipher_ctx(desc->tfm);
150	struct blkcipher_walk w;
151
152	blkcipher_walk_init(&w, dst, src, nbytes);
153	return crypt(desc, &w, ctx, crypto_cipher_alg(ctx->tweak)->cia_encrypt,
154		     crypto_cipher_alg(ctx->child)->cia_encrypt);
155}
156
157static int decrypt(struct blkcipher_desc *desc, struct scatterlist *dst,
158		   struct scatterlist *src, unsigned int nbytes)
159{
160	struct priv *ctx = crypto_blkcipher_ctx(desc->tfm);
161	struct blkcipher_walk w;
162
163	blkcipher_walk_init(&w, dst, src, nbytes);
164	return crypt(desc, &w, ctx, crypto_cipher_alg(ctx->tweak)->cia_encrypt,
165		     crypto_cipher_alg(ctx->child)->cia_decrypt);
166}
167
168static int init_tfm(struct crypto_tfm *tfm)
169{
170	struct crypto_cipher *cipher;
171	struct crypto_instance *inst = (void *)tfm->__crt_alg;
172	struct crypto_spawn *spawn = crypto_instance_ctx(inst);
173	struct priv *ctx = crypto_tfm_ctx(tfm);
174	u32 *flags = &tfm->crt_flags;
175
176	cipher = crypto_spawn_cipher(spawn);
177	if (IS_ERR(cipher))
178		return PTR_ERR(cipher);
179
180	if (crypto_cipher_blocksize(cipher) != 16) {
181		*flags |= CRYPTO_TFM_RES_BAD_BLOCK_LEN;
182		crypto_free_cipher(cipher);
183		return -EINVAL;
184	}
185
186	ctx->child = cipher;
187
188	cipher = crypto_spawn_cipher(spawn);
189	if (IS_ERR(cipher)) {
190		crypto_free_cipher(ctx->child);
191		return PTR_ERR(cipher);
192	}
193
194	/* this check isn't really needed, leave it here just in case */
195	if (crypto_cipher_blocksize(cipher) != 16) {
196		crypto_free_cipher(cipher);
197		crypto_free_cipher(ctx->child);
198		*flags |= CRYPTO_TFM_RES_BAD_BLOCK_LEN;
199		return -EINVAL;
200	}
201
202	ctx->tweak = cipher;
203
204	return 0;
205}
206
207static void exit_tfm(struct crypto_tfm *tfm)
208{
209	struct priv *ctx = crypto_tfm_ctx(tfm);
210	crypto_free_cipher(ctx->child);
211	crypto_free_cipher(ctx->tweak);
212}
213
214static struct crypto_instance *alloc(struct rtattr **tb)
215{
216	struct crypto_instance *inst;
217	struct crypto_alg *alg;
218	int err;
219
220	err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_BLKCIPHER);
221	if (err)
222		return ERR_PTR(err);
223
224	alg = crypto_get_attr_alg(tb, CRYPTO_ALG_TYPE_CIPHER,
225				  CRYPTO_ALG_TYPE_MASK);
226	if (IS_ERR(alg))
227		return ERR_CAST(alg);
228
229	inst = crypto_alloc_instance("xts", alg);
230	if (IS_ERR(inst))
231		goto out_put_alg;
232
233	inst->alg.cra_flags = CRYPTO_ALG_TYPE_BLKCIPHER;
234	inst->alg.cra_priority = alg->cra_priority;
235	inst->alg.cra_blocksize = alg->cra_blocksize;
236
237	if (alg->cra_alignmask < 7)
238		inst->alg.cra_alignmask = 7;
239	else
240		inst->alg.cra_alignmask = alg->cra_alignmask;
241
242	inst->alg.cra_type = &crypto_blkcipher_type;
243
244	inst->alg.cra_blkcipher.ivsize = alg->cra_blocksize;
245	inst->alg.cra_blkcipher.min_keysize =
246		2 * alg->cra_cipher.cia_min_keysize;
247	inst->alg.cra_blkcipher.max_keysize =
248		2 * alg->cra_cipher.cia_max_keysize;
249
250	inst->alg.cra_ctxsize = sizeof(struct priv);
251
252	inst->alg.cra_init = init_tfm;
253	inst->alg.cra_exit = exit_tfm;
254
255	inst->alg.cra_blkcipher.setkey = setkey;
256	inst->alg.cra_blkcipher.encrypt = encrypt;
257	inst->alg.cra_blkcipher.decrypt = decrypt;
258
259out_put_alg:
260	crypto_mod_put(alg);
261	return inst;
262}
263
264static void free(struct crypto_instance *inst)
265{
266	crypto_drop_spawn(crypto_instance_ctx(inst));
267	kfree(inst);
268}
269
270static struct crypto_template crypto_tmpl = {
271	.name = "xts",
272	.alloc = alloc,
273	.free = free,
274	.module = THIS_MODULE,
275};
276
277static int __init crypto_module_init(void)
278{
279	return crypto_register_template(&crypto_tmpl);
280}
281
282static void __exit crypto_module_exit(void)
283{
284	crypto_unregister_template(&crypto_tmpl);
285}
286
287module_init(crypto_module_init);
288module_exit(crypto_module_exit);
289
290MODULE_LICENSE("GPL");
291MODULE_DESCRIPTION("XTS block cipher mode");
292