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  */
  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,
  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
 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
 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
 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
 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
 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
 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         /* We access the data as u32s when xoring. */
 264         alignmask = alg->cra_alignmask | (__alignof__(u32) - 1);
 265         inst->alg.base.cra_alignmask = alignmask;
 266         inst->alg.base.cra_priority = alg->cra_priority;
 267         inst->alg.base.cra_blocksize = alg->cra_blocksize;
 268
 269         inst->alg.digestsize = alg->cra_blocksize;
 270         inst->alg.descsize =
 271                 ALIGN(sizeof(struct cmac_desc_ctx), crypto_tfm_ctx_alignment())
 272                 + (alignmask & ~(crypto_tfm_ctx_alignment() - 1))
 273                 + alg->cra_blocksize * 2;
 274
 275         inst->alg.base.cra_ctxsize =
 276                 ALIGN(sizeof(struct cmac_tfm_ctx), crypto_tfm_ctx_alignment())
 277                 + ((alignmask | (__alignof__(__be64) - 1)) &
 278                    ~(crypto_tfm_ctx_alignment() - 1))
 279                 + alg->cra_blocksize * 2;
 280
 281         inst->alg.base.cra_init = cmac_init_tfm;
 282         inst->alg.base.cra_exit = cmac_exit_tfm;
 283
 284         inst->alg.init = crypto_cmac_digest_init;
 285         inst->alg.update = crypto_cmac_digest_update;
 286         inst->alg.final = crypto_cmac_digest_final;
 287         inst->alg.setkey = crypto_cmac_digest_setkey;
 288
 289         err = shash_register_instance(tmpl, inst);
 290         if (err) {
 291 out_free_inst:
 292                 shash_free_instance(shash_crypto_instance(inst));
 293         }
 294
 295 out_put_alg:
 296         crypto_mod_put(alg);
 297         return err;
 298 }
 299
 300 static struct crypto_template crypto_cmac_tmpl = {
 301         .name = "cmac",
 302         .create = cmac_create,
 303         .free = shash_free_instance,
 304         .module = THIS_MODULE,
 305 };
 306
 307 static int __init crypto_cmac_module_init(void)
 308 {
 309         return crypto_register_template(&crypto_cmac_tmpl);
 310 }
 311
 312 static void __exit crypto_cmac_module_exit(void)
 313 {
 314         crypto_unregister_template(&crypto_cmac_tmpl);
 315 }
 316
 317 module_init(crypto_cmac_module_init);
 318 module_exit(crypto_cmac_module_exit);
 319
 320 MODULE_LICENSE("GPL");
 321 MODULE_DESCRIPTION("CMAC keyed hash algorithm");
 322 MODULE_ALIAS_CRYPTO("cmac");