linux/crypto/keywrap.c
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   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, pt, 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, ct, ctlen);
  74 *      skcipher_request_set_crypt(req, &sg, &sg, ctlen, 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/cipher.h>
  89#include <crypto/internal/skcipher.h>
  90
  91struct crypto_kw_block {
  92#define SEMIBSIZE 8
  93        __be64 A;
  94        __be64 R;
  95};
  96
  97/*
  98 * Fast forward the SGL to the "end" length minus SEMIBSIZE.
  99 * The start in the SGL defined by the fast-forward is returned with
 100 * the walk variable
 101 */
 102static void crypto_kw_scatterlist_ff(struct scatter_walk *walk,
 103                                     struct scatterlist *sg,
 104                                     unsigned int end)
 105{
 106        unsigned int skip = 0;
 107
 108        /* The caller should only operate on full SEMIBLOCKs. */
 109        BUG_ON(end < SEMIBSIZE);
 110
 111        skip = end - SEMIBSIZE;
 112        while (sg) {
 113                if (sg->length > skip) {
 114                        scatterwalk_start(walk, sg);
 115                        scatterwalk_advance(walk, skip);
 116                        break;
 117                }
 118
 119                skip -= sg->length;
 120                sg = sg_next(sg);
 121        }
 122}
 123
 124static int crypto_kw_decrypt(struct skcipher_request *req)
 125{
 126        struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 127        struct crypto_cipher *cipher = skcipher_cipher_simple(tfm);
 128        struct crypto_kw_block block;
 129        struct scatterlist *src, *dst;
 130        u64 t = 6 * ((req->cryptlen) >> 3);
 131        unsigned int i;
 132        int ret = 0;
 133
 134        /*
 135         * Require at least 2 semiblocks (note, the 3rd semiblock that is
 136         * required by SP800-38F is the IV.
 137         */
 138        if (req->cryptlen < (2 * SEMIBSIZE) || req->cryptlen % SEMIBSIZE)
 139                return -EINVAL;
 140
 141        /* Place the IV into block A */
 142        memcpy(&block.A, req->iv, SEMIBSIZE);
 143
 144        /*
 145         * src scatterlist is read-only. dst scatterlist is r/w. During the
 146         * first loop, src points to req->src and dst to req->dst. For any
 147         * subsequent round, the code operates on req->dst only.
 148         */
 149        src = req->src;
 150        dst = req->dst;
 151
 152        for (i = 0; i < 6; i++) {
 153                struct scatter_walk src_walk, dst_walk;
 154                unsigned int nbytes = req->cryptlen;
 155
 156                while (nbytes) {
 157                        /* move pointer by nbytes in the SGL */
 158                        crypto_kw_scatterlist_ff(&src_walk, src, nbytes);
 159                        /* get the source block */
 160                        scatterwalk_copychunks(&block.R, &src_walk, SEMIBSIZE,
 161                                               false);
 162
 163                        /* perform KW operation: modify IV with counter */
 164                        block.A ^= cpu_to_be64(t);
 165                        t--;
 166                        /* perform KW operation: decrypt block */
 167                        crypto_cipher_decrypt_one(cipher, (u8 *)&block,
 168                                                  (u8 *)&block);
 169
 170                        /* move pointer by nbytes in the SGL */
 171                        crypto_kw_scatterlist_ff(&dst_walk, dst, nbytes);
 172                        /* Copy block->R into place */
 173                        scatterwalk_copychunks(&block.R, &dst_walk, SEMIBSIZE,
 174                                               true);
 175
 176                        nbytes -= SEMIBSIZE;
 177                }
 178
 179                /* we now start to operate on the dst SGL only */
 180                src = req->dst;
 181                dst = req->dst;
 182        }
 183
 184        /* Perform authentication check */
 185        if (block.A != cpu_to_be64(0xa6a6a6a6a6a6a6a6ULL))
 186                ret = -EBADMSG;
 187
 188        memzero_explicit(&block, sizeof(struct crypto_kw_block));
 189
 190        return ret;
 191}
 192
 193static int crypto_kw_encrypt(struct skcipher_request *req)
 194{
 195        struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 196        struct crypto_cipher *cipher = skcipher_cipher_simple(tfm);
 197        struct crypto_kw_block block;
 198        struct scatterlist *src, *dst;
 199        u64 t = 1;
 200        unsigned int i;
 201
 202        /*
 203         * Require at least 2 semiblocks (note, the 3rd semiblock that is
 204         * required by SP800-38F is the IV that occupies the first semiblock.
 205         * This means that the dst memory must be one semiblock larger than src.
 206         * Also ensure that the given data is aligned to semiblock.
 207         */
 208        if (req->cryptlen < (2 * SEMIBSIZE) || req->cryptlen % SEMIBSIZE)
 209                return -EINVAL;
 210
 211        /*
 212         * Place the predefined IV into block A -- for encrypt, the caller
 213         * does not need to provide an IV, but he needs to fetch the final IV.
 214         */
 215        block.A = cpu_to_be64(0xa6a6a6a6a6a6a6a6ULL);
 216
 217        /*
 218         * src scatterlist is read-only. dst scatterlist is r/w. During the
 219         * first loop, src points to req->src and dst to req->dst. For any
 220         * subsequent round, the code operates on req->dst only.
 221         */
 222        src = req->src;
 223        dst = req->dst;
 224
 225        for (i = 0; i < 6; i++) {
 226                struct scatter_walk src_walk, dst_walk;
 227                unsigned int nbytes = req->cryptlen;
 228
 229                scatterwalk_start(&src_walk, src);
 230                scatterwalk_start(&dst_walk, dst);
 231
 232                while (nbytes) {
 233                        /* get the source block */
 234                        scatterwalk_copychunks(&block.R, &src_walk, SEMIBSIZE,
 235                                               false);
 236
 237                        /* perform KW operation: encrypt block */
 238                        crypto_cipher_encrypt_one(cipher, (u8 *)&block,
 239                                                  (u8 *)&block);
 240                        /* perform KW operation: modify IV with counter */
 241                        block.A ^= cpu_to_be64(t);
 242                        t++;
 243
 244                        /* Copy block->R into place */
 245                        scatterwalk_copychunks(&block.R, &dst_walk, SEMIBSIZE,
 246                                               true);
 247
 248                        nbytes -= SEMIBSIZE;
 249                }
 250
 251                /* we now start to operate on the dst SGL only */
 252                src = req->dst;
 253                dst = req->dst;
 254        }
 255
 256        /* establish the IV for the caller to pick up */
 257        memcpy(req->iv, &block.A, SEMIBSIZE);
 258
 259        memzero_explicit(&block, sizeof(struct crypto_kw_block));
 260
 261        return 0;
 262}
 263
 264static int crypto_kw_create(struct crypto_template *tmpl, struct rtattr **tb)
 265{
 266        struct skcipher_instance *inst;
 267        struct crypto_alg *alg;
 268        int err;
 269
 270        inst = skcipher_alloc_instance_simple(tmpl, tb);
 271        if (IS_ERR(inst))
 272                return PTR_ERR(inst);
 273
 274        alg = skcipher_ialg_simple(inst);
 275
 276        err = -EINVAL;
 277        /* Section 5.1 requirement for KW */
 278        if (alg->cra_blocksize != sizeof(struct crypto_kw_block))
 279                goto out_free_inst;
 280
 281        inst->alg.base.cra_blocksize = SEMIBSIZE;
 282        inst->alg.base.cra_alignmask = 0;
 283        inst->alg.ivsize = SEMIBSIZE;
 284
 285        inst->alg.encrypt = crypto_kw_encrypt;
 286        inst->alg.decrypt = crypto_kw_decrypt;
 287
 288        err = skcipher_register_instance(tmpl, inst);
 289        if (err) {
 290out_free_inst:
 291                inst->free(inst);
 292        }
 293
 294        return err;
 295}
 296
 297static struct crypto_template crypto_kw_tmpl = {
 298        .name = "kw",
 299        .create = crypto_kw_create,
 300        .module = THIS_MODULE,
 301};
 302
 303static int __init crypto_kw_init(void)
 304{
 305        return crypto_register_template(&crypto_kw_tmpl);
 306}
 307
 308static void __exit crypto_kw_exit(void)
 309{
 310        crypto_unregister_template(&crypto_kw_tmpl);
 311}
 312
 313subsys_initcall(crypto_kw_init);
 314module_exit(crypto_kw_exit);
 315
 316MODULE_LICENSE("Dual BSD/GPL");
 317MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");
 318MODULE_DESCRIPTION("Key Wrapping (RFC3394 / NIST SP800-38F)");
 319MODULE_ALIAS_CRYPTO("kw");
 320MODULE_IMPORT_NS(CRYPTO_INTERNAL);
 321
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