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