linux/crypto/cmac.c
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   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 <linux/err.h>
  17#include <linux/kernel.h>
  18#include <linux/module.h>
  19
  20/*
  21 * +------------------------
  22 * | <parent tfm>
  23 * +------------------------
  24 * | cmac_tfm_ctx
  25 * +------------------------
  26 * | consts (block size * 2)
  27 * +------------------------
  28 */
  29struct cmac_tfm_ctx {
  30        struct crypto_cipher *child;
  31        u8 ctx[];
  32};
  33
  34/*
  35 * +------------------------
  36 * | <shash desc>
  37 * +------------------------
  38 * | cmac_desc_ctx
  39 * +------------------------
  40 * | odds (block size)
  41 * +------------------------
  42 * | prev (block size)
  43 * +------------------------
  44 */
  45struct cmac_desc_ctx {
  46        unsigned int len;
  47        u8 ctx[];
  48};
  49
  50static int crypto_cmac_digest_setkey(struct crypto_shash *parent,
  51                                     const u8 *inkey, unsigned int keylen)
  52{
  53        unsigned long alignmask = crypto_shash_alignmask(parent);
  54        struct cmac_tfm_ctx *ctx = crypto_shash_ctx(parent);
  55        unsigned int bs = crypto_shash_blocksize(parent);
  56        __be64 *consts = PTR_ALIGN((void *)ctx->ctx,
  57                                   (alignmask | (__alignof__(__be64) - 1)) + 1);
  58        u64 _const[2];
  59        int i, err = 0;
  60        u8 msb_mask, gfmask;
  61
  62        err = crypto_cipher_setkey(ctx->child, inkey, keylen);
  63        if (err)
  64                return err;
  65
  66        /* encrypt the zero block */
  67        memset(consts, 0, bs);
  68        crypto_cipher_encrypt_one(ctx->child, (u8 *)consts, (u8 *)consts);
  69
  70        switch (bs) {
  71        case 16:
  72                gfmask = 0x87;
  73                _const[0] = be64_to_cpu(consts[1]);
  74                _const[1] = be64_to_cpu(consts[0]);
  75
  76                /* gf(2^128) multiply zero-ciphertext with u and u^2 */
  77                for (i = 0; i < 4; i += 2) {
  78                        msb_mask = ((s64)_const[1] >> 63) & gfmask;
  79                        _const[1] = (_const[1] << 1) | (_const[0] >> 63);
  80                        _const[0] = (_const[0] << 1) ^ msb_mask;
  81
  82                        consts[i + 0] = cpu_to_be64(_const[1]);
  83                        consts[i + 1] = cpu_to_be64(_const[0]);
  84                }
  85
  86                break;
  87        case 8:
  88                gfmask = 0x1B;
  89                _const[0] = be64_to_cpu(consts[0]);
  90
  91                /* gf(2^64) multiply zero-ciphertext with u and u^2 */
  92                for (i = 0; i < 2; i++) {
  93                        msb_mask = ((s64)_const[0] >> 63) & gfmask;
  94                        _const[0] = (_const[0] << 1) ^ msb_mask;
  95
  96                        consts[i] = cpu_to_be64(_const[0]);
  97                }
  98
  99                break;
 100        }
 101
 102        return 0;
 103}
 104
 105static int crypto_cmac_digest_init(struct shash_desc *pdesc)
 106{
 107        unsigned long alignmask = crypto_shash_alignmask(pdesc->tfm);
 108        struct cmac_desc_ctx *ctx = shash_desc_ctx(pdesc);
 109        int bs = crypto_shash_blocksize(pdesc->tfm);
 110        u8 *prev = PTR_ALIGN((void *)ctx->ctx, alignmask + 1) + bs;
 111
 112        ctx->len = 0;
 113        memset(prev, 0, bs);
 114
 115        return 0;
 116}
 117
 118static int crypto_cmac_digest_update(struct shash_desc *pdesc, const u8 *p,
 119                                     unsigned int len)
 120{
 121        struct crypto_shash *parent = pdesc->tfm;
 122        unsigned long alignmask = crypto_shash_alignmask(parent);
 123        struct cmac_tfm_ctx *tctx = crypto_shash_ctx(parent);
 124        struct cmac_desc_ctx *ctx = shash_desc_ctx(pdesc);
 125        struct crypto_cipher *tfm = tctx->child;
 126        int bs = crypto_shash_blocksize(parent);
 127        u8 *odds = PTR_ALIGN((void *)ctx->ctx, alignmask + 1);
 128        u8 *prev = odds + bs;
 129
 130        /* checking the data can fill the block */
 131        if ((ctx->len + len) <= bs) {
 132                memcpy(odds + ctx->len, p, len);
 133                ctx->len += len;
 134                return 0;
 135        }
 136
 137        /* filling odds with new data and encrypting it */
 138        memcpy(odds + ctx->len, p, bs - ctx->len);
 139        len -= bs - ctx->len;
 140        p += bs - ctx->len;
 141
 142        crypto_xor(prev, odds, bs);
 143        crypto_cipher_encrypt_one(tfm, prev, prev);
 144
 145        /* clearing the length */
 146        ctx->len = 0;
 147
 148        /* encrypting the rest of data */
 149        while (len > bs) {
 150                crypto_xor(prev, p, bs);
 151                crypto_cipher_encrypt_one(tfm, prev, prev);
 152                p += bs;
 153                len -= bs;
 154        }
 155
 156        /* keeping the surplus of blocksize */
 157        if (len) {
 158                memcpy(odds, p, len);
 159                ctx->len = len;
 160        }
 161
 162        return 0;
 163}
 164
 165static int crypto_cmac_digest_final(struct shash_desc *pdesc, u8 *out)
 166{
 167        struct crypto_shash *parent = pdesc->tfm;
 168        unsigned long alignmask = crypto_shash_alignmask(parent);
 169        struct cmac_tfm_ctx *tctx = crypto_shash_ctx(parent);
 170        struct cmac_desc_ctx *ctx = shash_desc_ctx(pdesc);
 171        struct crypto_cipher *tfm = tctx->child;
 172        int bs = crypto_shash_blocksize(parent);
 173        u8 *consts = PTR_ALIGN((void *)tctx->ctx,
 174                               (alignmask | (__alignof__(__be64) - 1)) + 1);
 175        u8 *odds = PTR_ALIGN((void *)ctx->ctx, alignmask + 1);
 176        u8 *prev = odds + bs;
 177        unsigned int offset = 0;
 178
 179        if (ctx->len != bs) {
 180                unsigned int rlen;
 181                u8 *p = odds + ctx->len;
 182
 183                *p = 0x80;
 184                p++;
 185
 186                rlen = bs - ctx->len - 1;
 187                if (rlen)
 188                        memset(p, 0, rlen);
 189
 190                offset += bs;
 191        }
 192
 193        crypto_xor(prev, odds, bs);
 194        crypto_xor(prev, consts + offset, bs);
 195
 196        crypto_cipher_encrypt_one(tfm, out, prev);
 197
 198        return 0;
 199}
 200
 201static int cmac_init_tfm(struct crypto_tfm *tfm)
 202{
 203        struct crypto_cipher *cipher;
 204        struct crypto_instance *inst = (void *)tfm->__crt_alg;
 205        struct crypto_cipher_spawn *spawn = crypto_instance_ctx(inst);
 206        struct cmac_tfm_ctx *ctx = crypto_tfm_ctx(tfm);
 207
 208        cipher = crypto_spawn_cipher(spawn);
 209        if (IS_ERR(cipher))
 210                return PTR_ERR(cipher);
 211
 212        ctx->child = cipher;
 213
 214        return 0;
 215};
 216
 217static void cmac_exit_tfm(struct crypto_tfm *tfm)
 218{
 219        struct cmac_tfm_ctx *ctx = crypto_tfm_ctx(tfm);
 220        crypto_free_cipher(ctx->child);
 221}
 222
 223static int cmac_create(struct crypto_template *tmpl, struct rtattr **tb)
 224{
 225        struct shash_instance *inst;
 226        struct crypto_cipher_spawn *spawn;
 227        struct crypto_alg *alg;
 228        unsigned long alignmask;
 229        u32 mask;
 230        int err;
 231
 232        err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_SHASH, &mask);
 233        if (err)
 234                return err;
 235
 236        inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL);
 237        if (!inst)
 238                return -ENOMEM;
 239        spawn = shash_instance_ctx(inst);
 240
 241        err = crypto_grab_cipher(spawn, shash_crypto_instance(inst),
 242                                 crypto_attr_alg_name(tb[1]), 0, mask);
 243        if (err)
 244                goto err_free_inst;
 245        alg = crypto_spawn_cipher_alg(spawn);
 246
 247        switch (alg->cra_blocksize) {
 248        case 16:
 249        case 8:
 250                break;
 251        default:
 252                err = -EINVAL;
 253                goto err_free_inst;
 254        }
 255
 256        err = crypto_inst_setname(shash_crypto_instance(inst), tmpl->name, alg);
 257        if (err)
 258                goto err_free_inst;
 259
 260        alignmask = alg->cra_alignmask;
 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), crypto_tfm_ctx_alignment())
 273                + ((alignmask | (__alignof__(__be64) - 1)) &
 274                   ~(crypto_tfm_ctx_alignment() - 1))
 275                + alg->cra_blocksize * 2;
 276
 277        inst->alg.base.cra_init = cmac_init_tfm;
 278        inst->alg.base.cra_exit = cmac_exit_tfm;
 279
 280        inst->alg.init = crypto_cmac_digest_init;
 281        inst->alg.update = crypto_cmac_digest_update;
 282        inst->alg.final = crypto_cmac_digest_final;
 283        inst->alg.setkey = crypto_cmac_digest_setkey;
 284
 285        inst->free = shash_free_singlespawn_instance;
 286
 287        err = shash_register_instance(tmpl, inst);
 288        if (err) {
 289err_free_inst:
 290                shash_free_singlespawn_instance(inst);
 291        }
 292        return err;
 293}
 294
 295static struct crypto_template crypto_cmac_tmpl = {
 296        .name = "cmac",
 297        .create = cmac_create,
 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
 311subsys_initcall(crypto_cmac_module_init);
 312module_exit(crypto_cmac_module_exit);
 313
 314MODULE_LICENSE("GPL");
 315MODULE_DESCRIPTION("CMAC keyed hash algorithm");
 316MODULE_ALIAS_CRYPTO("cmac");
 317MODULE_IMPORT_NS(CRYPTO_INTERNAL);
 318
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