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         u8 A[SEMIBSIZE];
  97         u8 R[SEMIBSIZE];
  98 };
  99
 100 /* convert 64 bit integer into its string representation */
 101 static inline void crypto_kw_cpu_to_be64(u64 val, u8 *buf)
 102 {
 103         __be64 *a = (__be64 *)buf;
 104
 105         *a = cpu_to_be64(val);
 106 }
 107
 108 /*
 109  * Fast forward the SGL to the "end" length minus SEMIBSIZE.
 110  * The start in the SGL defined by the fast-forward is returned with
 111  * the walk variable
 112  */
 113 static void crypto_kw_scatterlist_ff(struct scatter_walk *walk,
 114                                      struct scatterlist *sg,
 115                                      unsigned int end)
 116 {
 117         unsigned int skip = 0;
 118
 119         /* The caller should only operate on full SEMIBLOCKs. */
 120         BUG_ON(end < SEMIBSIZE);
 121
 122         skip = end - SEMIBSIZE;
 123         while (sg) {
 124                 if (sg->length > skip) {
 125                         scatterwalk_start(walk, sg);
 126                         scatterwalk_advance(walk, skip);
 127                         break;
 128                 } else
 129                         skip -= sg->length;
 130
 131                 sg = sg_next(sg);
 132         }
 133 }
 134
 135 static int crypto_kw_decrypt(struct blkcipher_desc *desc,
 136                              struct scatterlist *dst, struct scatterlist *src,
 137                              unsigned int nbytes)
 138 {
 139         struct crypto_blkcipher *tfm = desc->tfm;
 140         struct crypto_kw_ctx *ctx = crypto_blkcipher_ctx(tfm);
 141         struct crypto_cipher *child = ctx->child;
 142
 143         unsigned long alignmask = max_t(unsigned long, SEMIBSIZE,
 144                                         crypto_cipher_alignmask(child));
 145         unsigned int i;
 146
 147         u8 blockbuf[sizeof(struct crypto_kw_block) + alignmask];
 148         struct crypto_kw_block *block = (struct crypto_kw_block *)
 149                                         PTR_ALIGN(blockbuf + 0, alignmask + 1);
 150
 151         u64 t = 6 * ((nbytes) >> 3);
 152         struct scatterlist *lsrc, *ldst;
 153         int ret = 0;
 154
 155         /*
 156          * Require at least 2 semiblocks (note, the 3rd semiblock that is
 157          * required by SP800-38F is the IV.
 158          */
 159         if (nbytes < (2 * SEMIBSIZE) || nbytes % SEMIBSIZE)
 160                 return -EINVAL;
 161
 162         /* Place the IV into block A */
 163         memcpy(block->A, desc->info, SEMIBSIZE);
 164
 165         /*
 166          * src scatterlist is read-only. dst scatterlist is r/w. During the
 167          * first loop, lsrc points to src and ldst to dst. For any
 168          * subsequent round, the code operates on dst only.
 169          */
 170         lsrc = src;
 171         ldst = dst;
 172
 173         for (i = 0; i < 6; i++) {
 174                 u8 tbe_buffer[SEMIBSIZE + alignmask];
 175                 /* alignment for the crypto_xor and the _to_be64 operation */
 176                 u8 *tbe = PTR_ALIGN(tbe_buffer + 0, alignmask + 1);
 177                 unsigned int tmp_nbytes = nbytes;
 178                 struct scatter_walk src_walk, dst_walk;
 179
 180                 while (tmp_nbytes) {
 181                         /* move pointer by tmp_nbytes in the SGL */
 182                         crypto_kw_scatterlist_ff(&src_walk, lsrc, tmp_nbytes);
 183                         /* get the source block */
 184                         scatterwalk_copychunks(block->R, &src_walk, SEMIBSIZE,
 185                                                false);
 186
 187                         /* perform KW operation: get counter as byte string */
 188                         crypto_kw_cpu_to_be64(t, tbe);
 189                         /* perform KW operation: modify IV with counter */
 190                         crypto_xor(block->A, tbe, SEMIBSIZE);
 191                         t--;
 192                         /* perform KW operation: decrypt block */
 193                         crypto_cipher_decrypt_one(child, (u8*)block,
 194                                                   (u8*)block);
 195
 196                         /* move pointer by tmp_nbytes in the SGL */
 197                         crypto_kw_scatterlist_ff(&dst_walk, ldst, tmp_nbytes);
 198                         /* Copy block->R into place */
 199                         scatterwalk_copychunks(block->R, &dst_walk, SEMIBSIZE,
 200                                                true);
 201
 202                         tmp_nbytes -= SEMIBSIZE;
 203                 }
 204
 205                 /* we now start to operate on the dst SGL only */
 206                 lsrc = dst;
 207                 ldst = dst;
 208         }
 209
 210         /* Perform authentication check */
 211         if (crypto_memneq("\xA6\xA6\xA6\xA6\xA6\xA6\xA6\xA6", block->A,
 212                           SEMIBSIZE))
 213                 ret = -EBADMSG;
 214
 215         memzero_explicit(&block, sizeof(struct crypto_kw_block));
 216
 217         return ret;
 218 }
 219
 220 static int crypto_kw_encrypt(struct blkcipher_desc *desc,
 221                              struct scatterlist *dst, struct scatterlist *src,
 222                              unsigned int nbytes)
 223 {
 224         struct crypto_blkcipher *tfm = desc->tfm;
 225         struct crypto_kw_ctx *ctx = crypto_blkcipher_ctx(tfm);
 226         struct crypto_cipher *child = ctx->child;
 227
 228         unsigned long alignmask = max_t(unsigned long, SEMIBSIZE,
 229                                         crypto_cipher_alignmask(child));
 230         unsigned int i;
 231
 232         u8 blockbuf[sizeof(struct crypto_kw_block) + alignmask];
 233         struct crypto_kw_block *block = (struct crypto_kw_block *)
 234                                         PTR_ALIGN(blockbuf + 0, alignmask + 1);
 235
 236         u64 t = 1;
 237         struct scatterlist *lsrc, *ldst;
 238
 239         /*
 240          * Require at least 2 semiblocks (note, the 3rd semiblock that is
 241          * required by SP800-38F is the IV that occupies the first semiblock.
 242          * This means that the dst memory must be one semiblock larger than src.
 243          * Also ensure that the given data is aligned to semiblock.
 244          */
 245         if (nbytes < (2 * SEMIBSIZE) || nbytes % SEMIBSIZE)
 246                 return -EINVAL;
 247
 248         /*
 249          * Place the predefined IV into block A -- for encrypt, the caller
 250          * does not need to provide an IV, but he needs to fetch the final IV.
 251          */
 252         memcpy(block->A, "\xA6\xA6\xA6\xA6\xA6\xA6\xA6\xA6", SEMIBSIZE);
 253
 254         /*
 255          * src scatterlist is read-only. dst scatterlist is r/w. During the
 256          * first loop, lsrc points to src and ldst to dst. For any
 257          * subsequent round, the code operates on dst only.
 258          */
 259         lsrc = src;
 260         ldst = dst;
 261
 262         for (i = 0; i < 6; i++) {
 263                 u8 tbe_buffer[SEMIBSIZE + alignmask];
 264                 u8 *tbe = PTR_ALIGN(tbe_buffer + 0, alignmask + 1);
 265                 unsigned int tmp_nbytes = nbytes;
 266                 struct scatter_walk src_walk, dst_walk;
 267
 268                 scatterwalk_start(&src_walk, lsrc);
 269                 scatterwalk_start(&dst_walk, ldst);
 270
 271                 while (tmp_nbytes) {
 272                         /* get the source block */
 273                         scatterwalk_copychunks(block->R, &src_walk, SEMIBSIZE,
 274                                                false);
 275
 276                         /* perform KW operation: encrypt block */
 277                         crypto_cipher_encrypt_one(child, (u8 *)block,
 278                                                   (u8 *)block);
 279                         /* perform KW operation: get counter as byte string */
 280                         crypto_kw_cpu_to_be64(t, tbe);
 281                         /* perform KW operation: modify IV with counter */
 282                         crypto_xor(block->A, tbe, SEMIBSIZE);
 283                         t++;
 284
 285                         /* Copy block->R into place */
 286                         scatterwalk_copychunks(block->R, &dst_walk, SEMIBSIZE,
 287                                                true);
 288
 289                         tmp_nbytes -= SEMIBSIZE;
 290                 }
 291
 292                 /* we now start to operate on the dst SGL only */
 293                 lsrc = dst;
 294                 ldst = dst;
 295         }
 296
 297         /* establish the IV for the caller to pick up */
 298         memcpy(desc->info, block->A, SEMIBSIZE);
 299
 300         memzero_explicit(&block, sizeof(struct crypto_kw_block));
 301
 302         return 0;
 303 }
 304
 305 static int crypto_kw_setkey(struct crypto_tfm *parent, const u8 *key,
 306                             unsigned int keylen)
 307 {
 308         struct crypto_kw_ctx *ctx = crypto_tfm_ctx(parent);
 309         struct crypto_cipher *child = ctx->child;
 310         int err;
 311
 312         crypto_cipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
 313         crypto_cipher_set_flags(child, crypto_tfm_get_flags(parent) &
 314                                        CRYPTO_TFM_REQ_MASK);
 315         err = crypto_cipher_setkey(child, key, keylen);
 316         crypto_tfm_set_flags(parent, crypto_cipher_get_flags(child) &
 317                                      CRYPTO_TFM_RES_MASK);
 318         return err;
 319 }
 320
 321 static int crypto_kw_init_tfm(struct crypto_tfm *tfm)
 322 {
 323         struct crypto_instance *inst = crypto_tfm_alg_instance(tfm);
 324         struct crypto_spawn *spawn = crypto_instance_ctx(inst);
 325         struct crypto_kw_ctx *ctx = crypto_tfm_ctx(tfm);
 326         struct crypto_cipher *cipher;
 327
 328         cipher = crypto_spawn_cipher(spawn);
 329         if (IS_ERR(cipher))
 330                 return PTR_ERR(cipher);
 331
 332         ctx->child = cipher;
 333         return 0;
 334 }
 335
 336 static void crypto_kw_exit_tfm(struct crypto_tfm *tfm)
 337 {
 338         struct crypto_kw_ctx *ctx = crypto_tfm_ctx(tfm);
 339
 340         crypto_free_cipher(ctx->child);
 341 }
 342
 343 static struct crypto_instance *crypto_kw_alloc(struct rtattr **tb)
 344 {
 345         struct crypto_instance *inst = NULL;
 346         struct crypto_alg *alg = NULL;
 347         int err;
 348
 349         err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_BLKCIPHER);
 350         if (err)
 351                 return ERR_PTR(err);
 352
 353         alg = crypto_get_attr_alg(tb, CRYPTO_ALG_TYPE_CIPHER,
 354                                   CRYPTO_ALG_TYPE_MASK);
 355         if (IS_ERR(alg))
 356                 return ERR_CAST(alg);
 357
 358         inst = ERR_PTR(-EINVAL);
 359         /* Section 5.1 requirement for KW */
 360         if (alg->cra_blocksize != sizeof(struct crypto_kw_block))
 361                 goto err;
 362
 363         inst = crypto_alloc_instance("kw", alg);
 364         if (IS_ERR(inst))
 365                 goto err;
 366
 367         inst->alg.cra_flags = CRYPTO_ALG_TYPE_BLKCIPHER;
 368         inst->alg.cra_priority = alg->cra_priority;
 369         inst->alg.cra_blocksize = SEMIBSIZE;
 370         inst->alg.cra_alignmask = 0;
 371         inst->alg.cra_type = &crypto_blkcipher_type;
 372         inst->alg.cra_blkcipher.ivsize = SEMIBSIZE;
 373         inst->alg.cra_blkcipher.min_keysize = alg->cra_cipher.cia_min_keysize;
 374         inst->alg.cra_blkcipher.max_keysize = alg->cra_cipher.cia_max_keysize;
 375
 376         inst->alg.cra_ctxsize = sizeof(struct crypto_kw_ctx);
 377
 378         inst->alg.cra_init = crypto_kw_init_tfm;
 379         inst->alg.cra_exit = crypto_kw_exit_tfm;
 380
 381         inst->alg.cra_blkcipher.setkey = crypto_kw_setkey;
 382         inst->alg.cra_blkcipher.encrypt = crypto_kw_encrypt;
 383         inst->alg.cra_blkcipher.decrypt = crypto_kw_decrypt;
 384
 385 err:
 386         crypto_mod_put(alg);
 387         return inst;
 388 }
 389
 390 static void crypto_kw_free(struct crypto_instance *inst)
 391 {
 392         crypto_drop_spawn(crypto_instance_ctx(inst));
 393         kfree(inst);
 394 }
 395
 396 static struct crypto_template crypto_kw_tmpl = {
 397         .name = "kw",
 398         .alloc = crypto_kw_alloc,
 399         .free = crypto_kw_free,
 400         .module = THIS_MODULE,
 401 };
 402
 403 static int __init crypto_kw_init(void)
 404 {
 405         return crypto_register_template(&crypto_kw_tmpl);
 406 }
 407
 408 static void __exit crypto_kw_exit(void)
 409 {
 410         crypto_unregister_template(&crypto_kw_tmpl);
 411 }
 412
 413 module_init(crypto_kw_init);
 414 module_exit(crypto_kw_exit);
 415
 416 MODULE_LICENSE("Dual BSD/GPL");
 417 MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");
 418 MODULE_DESCRIPTION("Key Wrapping (RFC3394 / NIST SP800-38F)");
 419 MODULE_ALIAS_CRYPTO("kw");