cmac.c

  1// SPDX-License-Identifier: GPL-2.0-or-later
  2/*
  3 * CMAC: Cipher Block Mode for Authentication
  4 *
  5 * Copyright © 2013 Jussi Kivilinna <jussi.kivilinna@iki.fi>
  6 *
  7 * Based on work by:
  8 *  Copyright © 2013 Tom St Denis <tstdenis@elliptictech.com>
  9 * Based on crypto/xcbc.c:
 10 *  Copyright © 2006 USAGI/WIDE Project,
 11 *   Author: Kazunori Miyazawa <miyazawa@linux-ipv6.org>
 12 */
 13
 14#include <crypto/internal/cipher.h>
 15#include <crypto/internal/hash.h>
 16#include <crypto/utils.h>
 17#include <linux/err.h>
 18#include <linux/kernel.h>
 19#include <linux/module.h>
 20#include <linux/slab.h>
 21#include <linux/string.h>
 22
 23/*
 24 * +------------------------
 25 * | <parent tfm>
 26 * +------------------------
 27 * | cmac_tfm_ctx
 28 * +------------------------
 29 * | consts (block size * 2)
 30 * +------------------------
 31 */
 32struct cmac_tfm_ctx {
 33	struct crypto_cipher *child;
 34	__be64 consts[];
 35};
 36
 37static int crypto_cmac_digest_setkey(struct crypto_shash *parent,
 38				     const u8 *inkey, unsigned int keylen)
 39{
 40	struct cmac_tfm_ctx *ctx = crypto_shash_ctx(parent);
 41	unsigned int bs = crypto_shash_blocksize(parent);
 42	__be64 *consts = ctx->consts;
 43	u64 _const[2];
 44	int i, err = 0;
 45	u8 msb_mask, gfmask;
 46
 47	err = crypto_cipher_setkey(ctx->child, inkey, keylen);
 48	if (err)
 49		return err;
 50
 51	/* encrypt the zero block */
 52	memset(consts, 0, bs);
 53	crypto_cipher_encrypt_one(ctx->child, (u8 *)consts, (u8 *)consts);
 54
 55	switch (bs) {
 56	case 16:
 57		gfmask = 0x87;
 58		_const[0] = be64_to_cpu(consts[1]);
 59		_const[1] = be64_to_cpu(consts[0]);
 60
 61		/* gf(2^128) multiply zero-ciphertext with u and u^2 */
 62		for (i = 0; i < 4; i += 2) {
 63			msb_mask = ((s64)_const[1] >> 63) & gfmask;
 64			_const[1] = (_const[1] << 1) | (_const[0] >> 63);
 65			_const[0] = (_const[0] << 1) ^ msb_mask;
 66
 67			consts[i + 0] = cpu_to_be64(_const[1]);
 68			consts[i + 1] = cpu_to_be64(_const[0]);
 69		}
 70
 71		break;
 72	case 8:
 73		gfmask = 0x1B;
 74		_const[0] = be64_to_cpu(consts[0]);
 75
 76		/* gf(2^64) multiply zero-ciphertext with u and u^2 */
 77		for (i = 0; i < 2; i++) {
 78			msb_mask = ((s64)_const[0] >> 63) & gfmask;
 79			_const[0] = (_const[0] << 1) ^ msb_mask;
 80
 81			consts[i] = cpu_to_be64(_const[0]);
 82		}
 83
 84		break;
 85	}
 86
 87	return 0;
 88}
 89
 90static int crypto_cmac_digest_init(struct shash_desc *pdesc)
 91{
 92	int bs = crypto_shash_blocksize(pdesc->tfm);
 93	u8 *prev = shash_desc_ctx(pdesc);
 94
 95	memset(prev, 0, bs);
 96	return 0;
 97}
 98
 99static int crypto_cmac_digest_update(struct shash_desc *pdesc, const u8 *p,
100				     unsigned int len)
101{
102	struct crypto_shash *parent = pdesc->tfm;
103	struct cmac_tfm_ctx *tctx = crypto_shash_ctx(parent);
104	struct crypto_cipher *tfm = tctx->child;
105	int bs = crypto_shash_blocksize(parent);
106	u8 *prev = shash_desc_ctx(pdesc);
107
108	do {
109		crypto_xor(prev, p, bs);
110		crypto_cipher_encrypt_one(tfm, prev, prev);
111		p += bs;
112		len -= bs;
113	} while (len >= bs);
114	return len;
115}
116
117static int crypto_cmac_digest_finup(struct shash_desc *pdesc, const u8 *src,
118				    unsigned int len, u8 *out)
119{
120	struct crypto_shash *parent = pdesc->tfm;
121	struct cmac_tfm_ctx *tctx = crypto_shash_ctx(parent);
122	struct crypto_cipher *tfm = tctx->child;
123	int bs = crypto_shash_blocksize(parent);
124	u8 *prev = shash_desc_ctx(pdesc);
125	unsigned int offset = 0;
126
127	crypto_xor(prev, src, len);
128	if (len != bs) {
129		prev[len] ^= 0x80;
130		offset += bs;
131	}
132	crypto_xor(prev, (const u8 *)tctx->consts + offset, bs);
133	crypto_cipher_encrypt_one(tfm, out, prev);
134	return 0;
135}
136
137static int cmac_init_tfm(struct crypto_shash *tfm)
138{
139	struct shash_instance *inst = shash_alg_instance(tfm);
140	struct cmac_tfm_ctx *ctx = crypto_shash_ctx(tfm);
141	struct crypto_cipher_spawn *spawn;
142	struct crypto_cipher *cipher;
143
144	spawn = shash_instance_ctx(inst);
145	cipher = crypto_spawn_cipher(spawn);
146	if (IS_ERR(cipher))
147		return PTR_ERR(cipher);
148
149	ctx->child = cipher;
150
151	return 0;
152}
153
154static int cmac_clone_tfm(struct crypto_shash *tfm, struct crypto_shash *otfm)
155{
156	struct cmac_tfm_ctx *octx = crypto_shash_ctx(otfm);
157	struct cmac_tfm_ctx *ctx = crypto_shash_ctx(tfm);
158	struct crypto_cipher *cipher;
159
160	cipher = crypto_clone_cipher(octx->child);
161	if (IS_ERR(cipher))
162		return PTR_ERR(cipher);
163
164	ctx->child = cipher;
165
166	return 0;
167}
168
169static void cmac_exit_tfm(struct crypto_shash *tfm)
170{
171	struct cmac_tfm_ctx *ctx = crypto_shash_ctx(tfm);
172	crypto_free_cipher(ctx->child);
173}
174
175static int cmac_create(struct crypto_template *tmpl, struct rtattr **tb)
176{
177	struct shash_instance *inst;
178	struct crypto_cipher_spawn *spawn;
179	struct crypto_alg *alg;
180	u32 mask;
181	int err;
182
183	err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_SHASH, &mask);
184	if (err)
185		return err;
186
187	inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL);
188	if (!inst)
189		return -ENOMEM;
190	spawn = shash_instance_ctx(inst);
191
192	err = crypto_grab_cipher(spawn, shash_crypto_instance(inst),
193				 crypto_attr_alg_name(tb[1]), 0, mask);
194	if (err)
195		goto err_free_inst;
196	alg = crypto_spawn_cipher_alg(spawn);
197
198	switch (alg->cra_blocksize) {
199	case 16:
200	case 8:
201		break;
202	default:
203		err = -EINVAL;
204		goto err_free_inst;
205	}
206
207	err = crypto_inst_setname(shash_crypto_instance(inst), tmpl->name, alg);
208	if (err)
209		goto err_free_inst;
210
211	inst->alg.base.cra_priority = alg->cra_priority;
212	inst->alg.base.cra_blocksize = alg->cra_blocksize;
213	inst->alg.base.cra_ctxsize = sizeof(struct cmac_tfm_ctx) +
214				     alg->cra_blocksize * 2;
215	inst->alg.base.cra_flags = CRYPTO_AHASH_ALG_BLOCK_ONLY |
216				   CRYPTO_AHASH_ALG_FINAL_NONZERO;
217
218	inst->alg.digestsize = alg->cra_blocksize;
219	inst->alg.descsize = alg->cra_blocksize;
220	inst->alg.init = crypto_cmac_digest_init;
221	inst->alg.update = crypto_cmac_digest_update;
222	inst->alg.finup = crypto_cmac_digest_finup;
223	inst->alg.setkey = crypto_cmac_digest_setkey;
224	inst->alg.init_tfm = cmac_init_tfm;
225	inst->alg.clone_tfm = cmac_clone_tfm;
226	inst->alg.exit_tfm = cmac_exit_tfm;
227
228	inst->free = shash_free_singlespawn_instance;
229
230	err = shash_register_instance(tmpl, inst);
231	if (err) {
232err_free_inst:
233		shash_free_singlespawn_instance(inst);
234	}
235	return err;
236}
237
238static struct crypto_template crypto_cmac_tmpl = {
239	.name = "cmac",
240	.create = cmac_create,
241	.module = THIS_MODULE,
242};
243
244static int __init crypto_cmac_module_init(void)
245{
246	return crypto_register_template(&crypto_cmac_tmpl);
247}
248
249static void __exit crypto_cmac_module_exit(void)
250{
251	crypto_unregister_template(&crypto_cmac_tmpl);
252}
253
254module_init(crypto_cmac_module_init);
255module_exit(crypto_cmac_module_exit);
256
257MODULE_LICENSE("GPL");
258MODULE_DESCRIPTION("CMAC keyed hash algorithm");
259MODULE_ALIAS_CRYPTO("cmac");
260MODULE_IMPORT_NS("CRYPTO_INTERNAL");