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 
crypto_cmac_digest_setkey(struct crypto_shash * parent,const u8 * inkey,unsigned int keylen)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,
61 				   (alignmask | (__alignof__(__be64) - 1)) + 1);
62 	u64 _const[2];
63 	int i, err = 0;
64 	u8 msb_mask, gfmask;
65 
66 	err = crypto_cipher_setkey(ctx->child, inkey, keylen);
67 	if (err)
68 		return err;
69 
70 	/* encrypt the zero block */
71 	memset(consts, 0, bs);
72 	crypto_cipher_encrypt_one(ctx->child, (u8 *)consts, (u8 *)consts);
73 
74 	switch (bs) {
75 	case 16:
76 		gfmask = 0x87;
77 		_const[0] = be64_to_cpu(consts[1]);
78 		_const[1] = be64_to_cpu(consts[0]);
79 
80 		/* gf(2^128) multiply zero-ciphertext with u and u^2 */
81 		for (i = 0; i < 4; i += 2) {
82 			msb_mask = ((s64)_const[1] >> 63) & gfmask;
83 			_const[1] = (_const[1] << 1) | (_const[0] >> 63);
84 			_const[0] = (_const[0] << 1) ^ msb_mask;
85 
86 			consts[i + 0] = cpu_to_be64(_const[1]);
87 			consts[i + 1] = cpu_to_be64(_const[0]);
88 		}
89 
90 		break;
91 	case 8:
92 		gfmask = 0x1B;
93 		_const[0] = be64_to_cpu(consts[0]);
94 
95 		/* gf(2^64) multiply zero-ciphertext with u and u^2 */
96 		for (i = 0; i < 2; i++) {
97 			msb_mask = ((s64)_const[0] >> 63) & gfmask;
98 			_const[0] = (_const[0] << 1) ^ msb_mask;
99 
100 			consts[i] = cpu_to_be64(_const[0]);
101 		}
102 
103 		break;
104 	}
105 
106 	return 0;
107 }
108 
crypto_cmac_digest_init(struct shash_desc * pdesc)109 static int crypto_cmac_digest_init(struct shash_desc *pdesc)
110 {
111 	unsigned long alignmask = crypto_shash_alignmask(pdesc->tfm);
112 	struct cmac_desc_ctx *ctx = shash_desc_ctx(pdesc);
113 	int bs = crypto_shash_blocksize(pdesc->tfm);
114 	u8 *prev = PTR_ALIGN((void *)ctx->ctx, alignmask + 1) + bs;
115 
116 	ctx->len = 0;
117 	memset(prev, 0, bs);
118 
119 	return 0;
120 }
121 
crypto_cmac_digest_update(struct shash_desc * pdesc,const u8 * p,unsigned int len)122 static int crypto_cmac_digest_update(struct shash_desc *pdesc, const u8 *p,
123 				     unsigned int len)
124 {
125 	struct crypto_shash *parent = pdesc->tfm;
126 	unsigned long alignmask = crypto_shash_alignmask(parent);
127 	struct cmac_tfm_ctx *tctx = crypto_shash_ctx(parent);
128 	struct cmac_desc_ctx *ctx = shash_desc_ctx(pdesc);
129 	struct crypto_cipher *tfm = tctx->child;
130 	int bs = crypto_shash_blocksize(parent);
131 	u8 *odds = PTR_ALIGN((void *)ctx->ctx, alignmask + 1);
132 	u8 *prev = odds + bs;
133 
134 	/* checking the data can fill the block */
135 	if ((ctx->len + len) <= bs) {
136 		memcpy(odds + ctx->len, p, len);
137 		ctx->len += len;
138 		return 0;
139 	}
140 
141 	/* filling odds with new data and encrypting it */
142 	memcpy(odds + ctx->len, p, bs - ctx->len);
143 	len -= bs - ctx->len;
144 	p += bs - ctx->len;
145 
146 	crypto_xor(prev, odds, bs);
147 	crypto_cipher_encrypt_one(tfm, prev, prev);
148 
149 	/* clearing the length */
150 	ctx->len = 0;
151 
152 	/* encrypting the rest of data */
153 	while (len > bs) {
154 		crypto_xor(prev, p, bs);
155 		crypto_cipher_encrypt_one(tfm, prev, prev);
156 		p += bs;
157 		len -= bs;
158 	}
159 
160 	/* keeping the surplus of blocksize */
161 	if (len) {
162 		memcpy(odds, p, len);
163 		ctx->len = len;
164 	}
165 
166 	return 0;
167 }
168 
crypto_cmac_digest_final(struct shash_desc * pdesc,u8 * out)169 static int crypto_cmac_digest_final(struct shash_desc *pdesc, u8 *out)
170 {
171 	struct crypto_shash *parent = pdesc->tfm;
172 	unsigned long alignmask = crypto_shash_alignmask(parent);
173 	struct cmac_tfm_ctx *tctx = crypto_shash_ctx(parent);
174 	struct cmac_desc_ctx *ctx = shash_desc_ctx(pdesc);
175 	struct crypto_cipher *tfm = tctx->child;
176 	int bs = crypto_shash_blocksize(parent);
177 	u8 *consts = PTR_ALIGN((void *)tctx->ctx,
178 			       (alignmask | (__alignof__(__be64) - 1)) + 1);
179 	u8 *odds = PTR_ALIGN((void *)ctx->ctx, alignmask + 1);
180 	u8 *prev = odds + bs;
181 	unsigned int offset = 0;
182 
183 	if (ctx->len != bs) {
184 		unsigned int rlen;
185 		u8 *p = odds + ctx->len;
186 
187 		*p = 0x80;
188 		p++;
189 
190 		rlen = bs - ctx->len - 1;
191 		if (rlen)
192 			memset(p, 0, rlen);
193 
194 		offset += bs;
195 	}
196 
197 	crypto_xor(prev, odds, bs);
198 	crypto_xor(prev, consts + offset, bs);
199 
200 	crypto_cipher_encrypt_one(tfm, out, prev);
201 
202 	return 0;
203 }
204 
cmac_init_tfm(struct crypto_tfm * tfm)205 static int cmac_init_tfm(struct crypto_tfm *tfm)
206 {
207 	struct crypto_cipher *cipher;
208 	struct crypto_instance *inst = (void *)tfm->__crt_alg;
209 	struct crypto_spawn *spawn = crypto_instance_ctx(inst);
210 	struct cmac_tfm_ctx *ctx = crypto_tfm_ctx(tfm);
211 
212 	cipher = crypto_spawn_cipher(spawn);
213 	if (IS_ERR(cipher))
214 		return PTR_ERR(cipher);
215 
216 	ctx->child = cipher;
217 
218 	return 0;
219 };
220 
cmac_exit_tfm(struct crypto_tfm * tfm)221 static void cmac_exit_tfm(struct crypto_tfm *tfm)
222 {
223 	struct cmac_tfm_ctx *ctx = crypto_tfm_ctx(tfm);
224 	crypto_free_cipher(ctx->child);
225 }
226 
cmac_create(struct crypto_template * tmpl,struct rtattr ** tb)227 static int cmac_create(struct crypto_template *tmpl, struct rtattr **tb)
228 {
229 	struct shash_instance *inst;
230 	struct crypto_alg *alg;
231 	unsigned long alignmask;
232 	int err;
233 
234 	err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_SHASH);
235 	if (err)
236 		return err;
237 
238 	alg = crypto_get_attr_alg(tb, CRYPTO_ALG_TYPE_CIPHER,
239 				  CRYPTO_ALG_TYPE_MASK);
240 	if (IS_ERR(alg))
241 		return PTR_ERR(alg);
242 
243 	switch (alg->cra_blocksize) {
244 	case 16:
245 	case 8:
246 		break;
247 	default:
248 		err = -EINVAL;
249 		goto out_put_alg;
250 	}
251 
252 	inst = shash_alloc_instance("cmac", alg);
253 	err = PTR_ERR(inst);
254 	if (IS_ERR(inst))
255 		goto out_put_alg;
256 
257 	err = crypto_init_spawn(shash_instance_ctx(inst), alg,
258 				shash_crypto_instance(inst),
259 				CRYPTO_ALG_TYPE_MASK);
260 	if (err)
261 		goto out_free_inst;
262 
263 	alignmask = alg->cra_alignmask;
264 	inst->alg.base.cra_alignmask = alignmask;
265 	inst->alg.base.cra_priority = alg->cra_priority;
266 	inst->alg.base.cra_blocksize = alg->cra_blocksize;
267 
268 	inst->alg.digestsize = alg->cra_blocksize;
269 	inst->alg.descsize =
270 		ALIGN(sizeof(struct cmac_desc_ctx), crypto_tfm_ctx_alignment())
271 		+ (alignmask & ~(crypto_tfm_ctx_alignment() - 1))
272 		+ alg->cra_blocksize * 2;
273 
274 	inst->alg.base.cra_ctxsize =
275 		ALIGN(sizeof(struct cmac_tfm_ctx), crypto_tfm_ctx_alignment())
276 		+ ((alignmask | (__alignof__(__be64) - 1)) &
277 		   ~(crypto_tfm_ctx_alignment() - 1))
278 		+ alg->cra_blocksize * 2;
279 
280 	inst->alg.base.cra_init = cmac_init_tfm;
281 	inst->alg.base.cra_exit = cmac_exit_tfm;
282 
283 	inst->alg.init = crypto_cmac_digest_init;
284 	inst->alg.update = crypto_cmac_digest_update;
285 	inst->alg.final = crypto_cmac_digest_final;
286 	inst->alg.setkey = crypto_cmac_digest_setkey;
287 
288 	err = shash_register_instance(tmpl, inst);
289 	if (err) {
290 out_free_inst:
291 		shash_free_instance(shash_crypto_instance(inst));
292 	}
293 
294 out_put_alg:
295 	crypto_mod_put(alg);
296 	return err;
297 }
298 
299 static struct crypto_template crypto_cmac_tmpl = {
300 	.name = "cmac",
301 	.create = cmac_create,
302 	.free = shash_free_instance,
303 	.module = THIS_MODULE,
304 };
305 
crypto_cmac_module_init(void)306 static int __init crypto_cmac_module_init(void)
307 {
308 	return crypto_register_template(&crypto_cmac_tmpl);
309 }
310 
crypto_cmac_module_exit(void)311 static void __exit crypto_cmac_module_exit(void)
312 {
313 	crypto_unregister_template(&crypto_cmac_tmpl);
314 }
315 
316 module_init(crypto_cmac_module_init);
317 module_exit(crypto_cmac_module_exit);
318 
319 MODULE_LICENSE("GPL");
320 MODULE_DESCRIPTION("CMAC keyed hash algorithm");
321 MODULE_ALIAS_CRYPTO("cmac");
322