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Linux/crypto/cmac.c

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  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 

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