LXR linux/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
  90struct crypto_kw_ctx {
  91        struct crypto_cipher *child;
  92};
  93
  94struct 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 */
 101static 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 */
 113static 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
 135static 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
 220static 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
 305static 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
 321static 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
 336static 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
 343static 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
 385err:
 386        crypto_mod_put(alg);
 387        return inst;
 388}
 389
 390static void crypto_kw_free(struct crypto_instance *inst)
 391{
 392        crypto_drop_spawn(crypto_instance_ctx(inst));
 393        kfree(inst);
 394}
 395
 396static 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
 403static int __init crypto_kw_init(void)
 404{
 405        return crypto_register_template(&crypto_kw_tmpl);
 406}
 407
 408static void __exit crypto_kw_exit(void)
 409{
 410        crypto_unregister_template(&crypto_kw_tmpl);
 411}
 412
 413module_init(crypto_kw_init);
 414module_exit(crypto_kw_exit);
 415
 416MODULE_LICENSE("Dual BSD/GPL");
 417MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");
 418MODULE_DESCRIPTION("Key Wrapping (RFC3394 / NIST SP800-38F)");
 419MODULE_ALIAS_CRYPTO("kw");
 420