xref: /linux/crypto/cmac.c (revision 4949009eb8d40a441dcddcd96e101e77d31cf1b2)
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  */
33 struct 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  */
49 struct cmac_desc_ctx {
50 	unsigned int len;
51 	u8 ctx[];
52 };
53 
54 static 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 
108 static 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 
121 static 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 
168 static 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 
203 static 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 
219 static 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 
225 static 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) {
285 out_free_inst:
286 		shash_free_instance(shash_crypto_instance(inst));
287 	}
288 
289 out_put_alg:
290 	crypto_mod_put(alg);
291 	return err;
292 }
293 
294 static struct crypto_template crypto_cmac_tmpl = {
295 	.name = "cmac",
296 	.create = cmac_create,
297 	.free = shash_free_instance,
298 	.module = THIS_MODULE,
299 };
300 
301 static int __init crypto_cmac_module_init(void)
302 {
303 	return crypto_register_template(&crypto_cmac_tmpl);
304 }
305 
306 static void __exit crypto_cmac_module_exit(void)
307 {
308 	crypto_unregister_template(&crypto_cmac_tmpl);
309 }
310 
311 module_init(crypto_cmac_module_init);
312 module_exit(crypto_cmac_module_exit);
313 
314 MODULE_LICENSE("GPL");
315 MODULE_DESCRIPTION("CMAC keyed hash algorithm");
316 MODULE_ALIAS_CRYPTO("cmac");
317