Root/crypto/cmac.c

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");
316

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