crypto/keywrap.c

   1 /*
   2  * Key Wrapping: RFC3394 / NIST SP800-38F
   3  *
   4  * Copyright (C) 2015, Stephan Mueller <smueller@chronox.de>
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  * 1. Redistributions of source code must retain the above copyright
  10  *    notice, and the entire permission notice in its entirety,
  11  *    including the disclaimer of warranties.
  12  * 2. Redistributions in binary form must reproduce the above copyright
  13  *    notice, this list of conditions and the following disclaimer in the
  14  *    documentation and/or other materials provided with the distribution.
  15  * 3. The name of the author may not be used to endorse or promote
  16  *    products derived from this software without specific prior
  17  *    written permission.
  18  *
  19  * ALTERNATIVELY, this product may be distributed under the terms of
  20  * the GNU General Public License, in which case the provisions of the GPL2
  21  * are required INSTEAD OF the above restrictions.  (This clause is
  22  * necessary due to a potential bad interaction between the GPL and
  23  * the restrictions contained in a BSD-style copyright.)
  24  *
  25  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
  26  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  27  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF
  28  * WHICH ARE HEREBY DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE
  29  * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  30  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
  31  * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
  32  * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
  33  * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  34  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
  35  * USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH
  36  * DAMAGE.
  37  */
  38
  39 /*
  40  * Note for using key wrapping:
  41  *
  42  *      * The result of the encryption operation is the ciphertext starting
  43  *        with the 2nd semiblock. The first semiblock is provided as the IV.
  44  *        The IV used to start the encryption operation is the default IV.
  45  *
  46  *      * The input for the decryption is the first semiblock handed in as an
  47  *        IV. The ciphertext is the data starting with the 2nd semiblock. The
  48  *        return code of the decryption operation will be EBADMSG in case an
  49  *        integrity error occurs.
  50  *
  51  * To obtain the full result of an encryption as expected by SP800-38F, the
  52  * caller must allocate a buffer of plaintext + 8 bytes:
  53  *
  54  *      unsigned int datalen = ptlen + crypto_skcipher_ivsize(tfm);
  55  *      u8 data[datalen];
  56  *      u8 *iv = data;
  57  *      u8 *pt = data + crypto_skcipher_ivsize(tfm);
  58  *              <ensure that pt contains the plaintext of size ptlen>
  59  *      sg_init_one(&sg, ptdata, ptlen);
  60  *      skcipher_request_set_crypt(req, &sg, &sg, ptlen, iv);
  61  *
  62  *      ==> After encryption, data now contains full KW result as per SP800-38F.
  63  *
  64  * In case of decryption, ciphertext now already has the expected length
  65  * and must be segmented appropriately:
  66  *
  67  *      unsigned int datalen = CTLEN;
  68  *      u8 data[datalen];
  69  *              <ensure that data contains full ciphertext>
  70  *      u8 *iv = data;
  71  *      u8 *ct = data + crypto_skcipher_ivsize(tfm);
  72  *      unsigned int ctlen = datalen - crypto_skcipher_ivsize(tfm);
  73  *      sg_init_one(&sg, ctdata, ctlen);
  74  *      skcipher_request_set_crypt(req, &sg, &sg, ptlen, iv);
  75  *
  76  *      ==> After decryption (which hopefully does not return EBADMSG), the ct
  77  *      pointer now points to the plaintext of size ctlen.
  78  *
  79  * Note 2: KWP is not implemented as this would defy in-place operation.
  80  *         If somebody wants to wrap non-aligned data, he should simply pad
  81  *         the input with zeros to fill it up to the 8 byte boundary.
  82  */
  83
  84 #include <linux/module.h>
  85 #include <linux/crypto.h>
  86 #include <linux/scatterlist.h>
  87 #include <crypto/scatterwalk.h>
  88 #include <crypto/internal/skcipher.h>
  89
  90 struct crypto_kw_ctx {
  91         struct crypto_cipher *child;
  92 };
  93
  94 struct crypto_kw_block {
  95 #define SEMIBSIZE 8
  96         __be64 A;
  97         __be64 R;
  98 };
  99
 100 /*
 101  * Fast forward the SGL to the "end" length minus SEMIBSIZE.
 102  * The start in the SGL defined by the fast-forward is returned with
 103  * the walk variable
 104  */
 105 static void crypto_kw_scatterlist_ff(struct scatter_walk *walk,
 106                                      struct scatterlist *sg,
 107                                      unsigned int end)
 108 {
 109         unsigned int skip = 0;
 110
 111         /* The caller should only operate on full SEMIBLOCKs. */
 112         BUG_ON(end < SEMIBSIZE);
 113
 114         skip = end - SEMIBSIZE;
 115         while (sg) {
 116                 if (sg->length > skip) {
 117                         scatterwalk_start(walk, sg);
 118                         scatterwalk_advance(walk, skip);
 119                         break;
 120                 } else
 121                         skip -= sg->length;
 122
 123                 sg = sg_next(sg);
 124         }
 125 }
 126
 127 static int crypto_kw_decrypt(struct blkcipher_desc *desc,
 128                              struct scatterlist *dst, struct scatterlist *src,
 129                              unsigned int nbytes)
 130 {
 131         struct crypto_blkcipher *tfm = desc->tfm;
 132         struct crypto_kw_ctx *ctx = crypto_blkcipher_ctx(tfm);
 133         struct crypto_cipher *child = ctx->child;
 134         struct crypto_kw_block block;
 135         struct scatterlist *lsrc, *ldst;
 136         u64 t = 6 * ((nbytes) >> 3);
 137         unsigned int i;
 138         int ret = 0;
 139
 140         /*
 141          * Require at least 2 semiblocks (note, the 3rd semiblock that is
 142          * required by SP800-38F is the IV.
 143          */
 144         if (nbytes < (2 * SEMIBSIZE) || nbytes % SEMIBSIZE)
 145                 return -EINVAL;
 146
 147         /* Place the IV into block A */
 148         memcpy(&block.A, desc->info, SEMIBSIZE);
 149
 150         /*
 151          * src scatterlist is read-only. dst scatterlist is r/w. During the
 152          * first loop, lsrc points to src and ldst to dst. For any
 153          * subsequent round, the code operates on dst only.
 154          */
 155         lsrc = src;
 156         ldst = dst;
 157
 158         for (i = 0; i < 6; i++) {
 159                 struct scatter_walk src_walk, dst_walk;
 160                 unsigned int tmp_nbytes = nbytes;
 161
 162                 while (tmp_nbytes) {
 163                         /* move pointer by tmp_nbytes in the SGL */
 164                         crypto_kw_scatterlist_ff(&src_walk, lsrc, tmp_nbytes);
 165                         /* get the source block */
 166                         scatterwalk_copychunks(&block.R, &src_walk, SEMIBSIZE,
 167                                                false);
 168
 169                         /* perform KW operation: modify IV with counter */
 170                         block.A ^= cpu_to_be64(t);
 171                         t--;
 172                         /* perform KW operation: decrypt block */
 173                         crypto_cipher_decrypt_one(child, (u8*)&block,
 174                                                   (u8*)&block);
 175
 176                         /* move pointer by tmp_nbytes in the SGL */
 177                         crypto_kw_scatterlist_ff(&dst_walk, ldst, tmp_nbytes);
 178                         /* Copy block->R into place */
 179                         scatterwalk_copychunks(&block.R, &dst_walk, SEMIBSIZE,
 180                                                true);
 181
 182                         tmp_nbytes -= SEMIBSIZE;
 183                 }
 184
 185                 /* we now start to operate on the dst SGL only */
 186                 lsrc = dst;
 187                 ldst = dst;
 188         }
 189
 190         /* Perform authentication check */
 191         if (block.A != cpu_to_be64(0xa6a6a6a6a6a6a6a6))
 192                 ret = -EBADMSG;
 193
 194         memzero_explicit(&block, sizeof(struct crypto_kw_block));
 195
 196         return ret;
 197 }
 198
 199 static int crypto_kw_encrypt(struct blkcipher_desc *desc,
 200                              struct scatterlist *dst, struct scatterlist *src,
 201                              unsigned int nbytes)
 202 {
 203         struct crypto_blkcipher *tfm = desc->tfm;
 204         struct crypto_kw_ctx *ctx = crypto_blkcipher_ctx(tfm);
 205         struct crypto_cipher *child = ctx->child;
 206         struct crypto_kw_block block;
 207         struct scatterlist *lsrc, *ldst;
 208         u64 t = 1;
 209         unsigned int i;
 210
 211         /*
 212          * Require at least 2 semiblocks (note, the 3rd semiblock that is
 213          * required by SP800-38F is the IV that occupies the first semiblock.
 214          * This means that the dst memory must be one semiblock larger than src.
 215          * Also ensure that the given data is aligned to semiblock.
 216          */
 217         if (nbytes < (2 * SEMIBSIZE) || nbytes % SEMIBSIZE)
 218                 return -EINVAL;
 219
 220         /*
 221          * Place the predefined IV into block A -- for encrypt, the caller
 222          * does not need to provide an IV, but he needs to fetch the final IV.
 223          */
 224         block.A = cpu_to_be64(0xa6a6a6a6a6a6a6a6);
 225
 226         /*
 227          * src scatterlist is read-only. dst scatterlist is r/w. During the
 228          * first loop, lsrc points to src and ldst to dst. For any
 229          * subsequent round, the code operates on dst only.
 230          */
 231         lsrc = src;
 232         ldst = dst;
 233
 234         for (i = 0; i < 6; i++) {
 235                 struct scatter_walk src_walk, dst_walk;
 236                 unsigned int tmp_nbytes = nbytes;
 237
 238                 scatterwalk_start(&src_walk, lsrc);
 239                 scatterwalk_start(&dst_walk, ldst);
 240
 241                 while (tmp_nbytes) {
 242                         /* get the source block */
 243                         scatterwalk_copychunks(&block.R, &src_walk, SEMIBSIZE,
 244                                                false);
 245
 246                         /* perform KW operation: encrypt block */
 247                         crypto_cipher_encrypt_one(child, (u8 *)&block,
 248                                                   (u8 *)&block);
 249                         /* perform KW operation: modify IV with counter */
 250                         block.A ^= cpu_to_be64(t);
 251                         t++;
 252
 253                         /* Copy block->R into place */
 254                         scatterwalk_copychunks(&block.R, &dst_walk, SEMIBSIZE,
 255                                                true);
 256
 257                         tmp_nbytes -= SEMIBSIZE;
 258                 }
 259
 260                 /* we now start to operate on the dst SGL only */
 261                 lsrc = dst;
 262                 ldst = dst;
 263         }
 264
 265         /* establish the IV for the caller to pick up */
 266         memcpy(desc->info, &block.A, SEMIBSIZE);
 267
 268         memzero_explicit(&block, sizeof(struct crypto_kw_block));
 269
 270         return 0;
 271 }
 272
 273 static int crypto_kw_setkey(struct crypto_tfm *parent, const u8 *key,
 274                             unsigned int keylen)
 275 {
 276         struct crypto_kw_ctx *ctx = crypto_tfm_ctx(parent);
 277         struct crypto_cipher *child = ctx->child;
 278         int err;
 279
 280         crypto_cipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
 281         crypto_cipher_set_flags(child, crypto_tfm_get_flags(parent) &
 282                                        CRYPTO_TFM_REQ_MASK);
 283         err = crypto_cipher_setkey(child, key, keylen);
 284         crypto_tfm_set_flags(parent, crypto_cipher_get_flags(child) &
 285                                      CRYPTO_TFM_RES_MASK);
 286         return err;
 287 }
 288
 289 static int crypto_kw_init_tfm(struct crypto_tfm *tfm)
 290 {
 291         struct crypto_instance *inst = crypto_tfm_alg_instance(tfm);
 292         struct crypto_spawn *spawn = crypto_instance_ctx(inst);
 293         struct crypto_kw_ctx *ctx = crypto_tfm_ctx(tfm);
 294         struct crypto_cipher *cipher;
 295
 296         cipher = crypto_spawn_cipher(spawn);
 297         if (IS_ERR(cipher))
 298                 return PTR_ERR(cipher);
 299
 300         ctx->child = cipher;
 301         return 0;
 302 }
 303
 304 static void crypto_kw_exit_tfm(struct crypto_tfm *tfm)
 305 {
 306         struct crypto_kw_ctx *ctx = crypto_tfm_ctx(tfm);
 307
 308         crypto_free_cipher(ctx->child);
 309 }
 310
 311 static struct crypto_instance *crypto_kw_alloc(struct rtattr **tb)
 312 {
 313         struct crypto_instance *inst = NULL;
 314         struct crypto_alg *alg = NULL;
 315         int err;
 316
 317         err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_BLKCIPHER);
 318         if (err)
 319                 return ERR_PTR(err);
 320
 321         alg = crypto_get_attr_alg(tb, CRYPTO_ALG_TYPE_CIPHER,
 322                                   CRYPTO_ALG_TYPE_MASK);
 323         if (IS_ERR(alg))
 324                 return ERR_CAST(alg);
 325
 326         inst = ERR_PTR(-EINVAL);
 327         /* Section 5.1 requirement for KW */
 328         if (alg->cra_blocksize != sizeof(struct crypto_kw_block))
 329                 goto err;
 330
 331         inst = crypto_alloc_instance("kw", alg);
 332         if (IS_ERR(inst))
 333                 goto err;
 334
 335         inst->alg.cra_flags = CRYPTO_ALG_TYPE_BLKCIPHER;
 336         inst->alg.cra_priority = alg->cra_priority;
 337         inst->alg.cra_blocksize = SEMIBSIZE;
 338         inst->alg.cra_alignmask = 0;
 339         inst->alg.cra_type = &crypto_blkcipher_type;
 340         inst->alg.cra_blkcipher.ivsize = SEMIBSIZE;
 341         inst->alg.cra_blkcipher.min_keysize = alg->cra_cipher.cia_min_keysize;
 342         inst->alg.cra_blkcipher.max_keysize = alg->cra_cipher.cia_max_keysize;
 343
 344         inst->alg.cra_ctxsize = sizeof(struct crypto_kw_ctx);
 345
 346         inst->alg.cra_init = crypto_kw_init_tfm;
 347         inst->alg.cra_exit = crypto_kw_exit_tfm;
 348
 349         inst->alg.cra_blkcipher.setkey = crypto_kw_setkey;
 350         inst->alg.cra_blkcipher.encrypt = crypto_kw_encrypt;
 351         inst->alg.cra_blkcipher.decrypt = crypto_kw_decrypt;
 352
 353 err:
 354         crypto_mod_put(alg);
 355         return inst;
 356 }
 357
 358 static void crypto_kw_free(struct crypto_instance *inst)
 359 {
 360         crypto_drop_spawn(crypto_instance_ctx(inst));
 361         kfree(inst);
 362 }
 363
 364 static struct crypto_template crypto_kw_tmpl = {
 365         .name = "kw",
 366         .alloc = crypto_kw_alloc,
 367         .free = crypto_kw_free,
 368         .module = THIS_MODULE,
 369 };
 370
 371 static int __init crypto_kw_init(void)
 372 {
 373         return crypto_register_template(&crypto_kw_tmpl);
 374 }
 375
 376 static void __exit crypto_kw_exit(void)
 377 {
 378         crypto_unregister_template(&crypto_kw_tmpl);
 379 }
 380
 381 module_init(crypto_kw_init);
 382 module_exit(crypto_kw_exit);
 383
 384 MODULE_LICENSE("Dual BSD/GPL");
 385 MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");
 386 MODULE_DESCRIPTION("Key Wrapping (RFC3394 / NIST SP800-38F)");
 387 MODULE_ALIAS_CRYPTO("kw");