1/*
2 * CMAC: Cipher Block Mode for Authentication
3 *
4 * Copyright © 2013 Jussi Kivilinna <jussi.kivilinna@iki.fi>
5 *
6 * Based on work by:
7 *  Copyright © 2013 Tom St Denis <tstdenis@elliptictech.com>
8 * Based on crypto/xcbc.c:
9 *  Copyright © 2006 USAGI/WIDE Project,
10 *   Author: Kazunori Miyazawa <miyazawa@linux-ipv6.org>
11 *
12 * This program is free software; you can redistribute it and/or modify
13 * it under the terms of the GNU General Public License as published by
14 * the Free Software Foundation; either version 2 of the License, or
15 * (at your option) any later version.
16 *
17 */
18
19#include <crypto/internal/hash.h>
20#include <linux/err.h>
21#include <linux/kernel.h>
22#include <linux/module.h>
23
24/*
25 * +------------------------
26 * | <parent tfm>
27 * +------------------------
28 * | cmac_tfm_ctx
29 * +------------------------
30 * | consts (block size * 2)
31 * +------------------------
32 */
33struct cmac_tfm_ctx {
34	struct crypto_cipher *child;
35	u8 ctx[];
36};
37
38/*
39 * +------------------------
40 * | <shash desc>
41 * +------------------------
42 * | cmac_desc_ctx
43 * +------------------------
44 * | odds (block size)
45 * +------------------------
46 * | prev (block size)
47 * +------------------------
48 */
49struct cmac_desc_ctx {
50	unsigned int len;
51	u8 ctx[];
52};
53
54static int crypto_cmac_digest_setkey(struct crypto_shash *parent,
55				     const u8 *inkey, unsigned int keylen)
56{
57	unsigned long alignmask = crypto_shash_alignmask(parent);
58	struct cmac_tfm_ctx *ctx = crypto_shash_ctx(parent);
59	unsigned int bs = crypto_shash_blocksize(parent);
60	__be64 *consts = PTR_ALIGN((void *)ctx->ctx, alignmask + 1);
61	u64 _const[2];
62	int i, err = 0;
63	u8 msb_mask, gfmask;
64
65	err = crypto_cipher_setkey(ctx->child, inkey, keylen);
66	if (err)
67		return err;
68
69	/* encrypt the zero block */
70	memset(consts, 0, bs);
71	crypto_cipher_encrypt_one(ctx->child, (u8 *)consts, (u8 *)consts);
72
73	switch (bs) {
74	case 16:
75		gfmask = 0x87;
76		_const[0] = be64_to_cpu(consts[1]);
77		_const[1] = be64_to_cpu(consts[0]);
78
79		/* gf(2^128) multiply zero-ciphertext with u and u^2 */
80		for (i = 0; i < 4; i += 2) {
81			msb_mask = ((s64)_const[1] >> 63) & gfmask;
82			_const[1] = (_const[1] << 1) | (_const[0] >> 63);
83			_const[0] = (_const[0] << 1) ^ msb_mask;
84
85			consts[i + 0] = cpu_to_be64(_const[1]);
86			consts[i + 1] = cpu_to_be64(_const[0]);
87		}
88
89		break;
90	case 8:
91		gfmask = 0x1B;
92		_const[0] = be64_to_cpu(consts[0]);
93
94		/* gf(2^64) multiply zero-ciphertext with u and u^2 */
95		for (i = 0; i < 2; i++) {
96			msb_mask = ((s64)_const[0] >> 63) & gfmask;
97			_const[0] = (_const[0] << 1) ^ msb_mask;
98
99			consts[i] = cpu_to_be64(_const[0]);
100		}
101
102		break;
103	}
104
105	return 0;
106}
107
108static int crypto_cmac_digest_init(struct shash_desc *pdesc)
109{
110	unsigned long alignmask = crypto_shash_alignmask(pdesc->tfm);
111	struct cmac_desc_ctx *ctx = shash_desc_ctx(pdesc);
112	int bs = crypto_shash_blocksize(pdesc->tfm);
113	u8 *prev = PTR_ALIGN((void *)ctx->ctx, alignmask + 1) + bs;
114
115	ctx->len = 0;
116	memset(prev, 0, bs);
117
118	return 0;
119}
120
121static int crypto_cmac_digest_update(struct shash_desc *pdesc, const u8 *p,
122				     unsigned int len)
123{
124	struct crypto_shash *parent = pdesc->tfm;
125	unsigned long alignmask = crypto_shash_alignmask(parent);
126	struct cmac_tfm_ctx *tctx = crypto_shash_ctx(parent);
127	struct cmac_desc_ctx *ctx = shash_desc_ctx(pdesc);
128	struct crypto_cipher *tfm = tctx->child;
129	int bs = crypto_shash_blocksize(parent);
130	u8 *odds = PTR_ALIGN((void *)ctx->ctx, alignmask + 1);
131	u8 *prev = odds + bs;
132
133	/* checking the data can fill the block */
134	if ((ctx->len + len) <= bs) {
135		memcpy(odds + ctx->len, p, len);
136		ctx->len += len;
137		return 0;
138	}
139
140	/* filling odds with new data and encrypting it */
141	memcpy(odds + ctx->len, p, bs - ctx->len);
142	len -= bs - ctx->len;
143	p += bs - ctx->len;
144
145	crypto_xor(prev, odds, bs);
146	crypto_cipher_encrypt_one(tfm, prev, prev);
147
148	/* clearing the length */
149	ctx->len = 0;
150
151	/* encrypting the rest of data */
152	while (len > bs) {
153		crypto_xor(prev, p, bs);
154		crypto_cipher_encrypt_one(tfm, prev, prev);
155		p += bs;
156		len -= bs;
157	}
158
159	/* keeping the surplus of blocksize */
160	if (len) {
161		memcpy(odds, p, len);
162		ctx->len = len;
163	}
164
165	return 0;
166}
167
168static int crypto_cmac_digest_final(struct shash_desc *pdesc, u8 *out)
169{
170	struct crypto_shash *parent = pdesc->tfm;
171	unsigned long alignmask = crypto_shash_alignmask(parent);
172	struct cmac_tfm_ctx *tctx = crypto_shash_ctx(parent);
173	struct cmac_desc_ctx *ctx = shash_desc_ctx(pdesc);
174	struct crypto_cipher *tfm = tctx->child;
175	int bs = crypto_shash_blocksize(parent);
176	u8 *consts = PTR_ALIGN((void *)tctx->ctx, alignmask + 1);
177	u8 *odds = PTR_ALIGN((void *)ctx->ctx, alignmask + 1);
178	u8 *prev = odds + bs;
179	unsigned int offset = 0;
180
181	if (ctx->len != bs) {
182		unsigned int rlen;
183		u8 *p = odds + ctx->len;
184
185		*p = 0x80;
186		p++;
187
188		rlen = bs - ctx->len - 1;
189		if (rlen)
190			memset(p, 0, rlen);
191
192		offset += bs;
193	}
194
195	crypto_xor(prev, odds, bs);
196	crypto_xor(prev, consts + offset, bs);
197
198	crypto_cipher_encrypt_one(tfm, out, prev);
199
200	return 0;
201}
202
203static int cmac_init_tfm(struct crypto_tfm *tfm)
204{
205	struct crypto_cipher *cipher;
206	struct crypto_instance *inst = (void *)tfm->__crt_alg;
207	struct crypto_spawn *spawn = crypto_instance_ctx(inst);
208	struct cmac_tfm_ctx *ctx = crypto_tfm_ctx(tfm);
209
210	cipher = crypto_spawn_cipher(spawn);
211	if (IS_ERR(cipher))
212		return PTR_ERR(cipher);
213
214	ctx->child = cipher;
215
216	return 0;
217};
218
219static void cmac_exit_tfm(struct crypto_tfm *tfm)
220{
221	struct cmac_tfm_ctx *ctx = crypto_tfm_ctx(tfm);
222	crypto_free_cipher(ctx->child);
223}
224
225static int cmac_create(struct crypto_template *tmpl, struct rtattr **tb)
226{
227	struct shash_instance *inst;
228	struct crypto_alg *alg;
229	unsigned long alignmask;
230	int err;
231
232	err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_SHASH);
233	if (err)
234		return err;
235
236	alg = crypto_get_attr_alg(tb, CRYPTO_ALG_TYPE_CIPHER,
237				  CRYPTO_ALG_TYPE_MASK);
238	if (IS_ERR(alg))
239		return PTR_ERR(alg);
240
241	switch (alg->cra_blocksize) {
242	case 16:
243	case 8:
244		break;
245	default:
246		goto out_put_alg;
247	}
248
249	inst = shash_alloc_instance("cmac", alg);
250	err = PTR_ERR(inst);
251	if (IS_ERR(inst))
252		goto out_put_alg;
253
254	err = crypto_init_spawn(shash_instance_ctx(inst), alg,
255				shash_crypto_instance(inst),
256				CRYPTO_ALG_TYPE_MASK);
257	if (err)
258		goto out_free_inst;
259
260	alignmask = alg->cra_alignmask | (sizeof(long) - 1);
261	inst->alg.base.cra_alignmask = alignmask;
262	inst->alg.base.cra_priority = alg->cra_priority;
263	inst->alg.base.cra_blocksize = alg->cra_blocksize;
264
265	inst->alg.digestsize = alg->cra_blocksize;
266	inst->alg.descsize =
267		ALIGN(sizeof(struct cmac_desc_ctx), crypto_tfm_ctx_alignment())
268		+ (alignmask & ~(crypto_tfm_ctx_alignment() - 1))
269		+ alg->cra_blocksize * 2;
270
271	inst->alg.base.cra_ctxsize =
272		ALIGN(sizeof(struct cmac_tfm_ctx), alignmask + 1)
273		+ alg->cra_blocksize * 2;
274
275	inst->alg.base.cra_init = cmac_init_tfm;
276	inst->alg.base.cra_exit = cmac_exit_tfm;
277
278	inst->alg.init = crypto_cmac_digest_init;
279	inst->alg.update = crypto_cmac_digest_update;
280	inst->alg.final = crypto_cmac_digest_final;
281	inst->alg.setkey = crypto_cmac_digest_setkey;
282
283	err = shash_register_instance(tmpl, inst);
284	if (err) {
285out_free_inst:
286		shash_free_instance(shash_crypto_instance(inst));
287	}
288
289out_put_alg:
290	crypto_mod_put(alg);
291	return err;
292}
293
294static struct crypto_template crypto_cmac_tmpl = {
295	.name = "cmac",
296	.create = cmac_create,
297	.free = shash_free_instance,
298	.module = THIS_MODULE,
299};
300
301static int __init crypto_cmac_module_init(void)
302{
303	return crypto_register_template(&crypto_cmac_tmpl);
304}
305
306static void __exit crypto_cmac_module_exit(void)
307{
308	crypto_unregister_template(&crypto_cmac_tmpl);
309}
310
311module_init(crypto_cmac_module_init);
312module_exit(crypto_cmac_module_exit);
313
314MODULE_LICENSE("GPL");
315MODULE_DESCRIPTION("CMAC keyed hash algorithm");
316MODULE_ALIAS_CRYPTO("cmac");
317