crypto/cts.c

   1 /*
   2  * CTS: Cipher Text Stealing mode
   3  *
   4  * COPYRIGHT (c) 2008
   5  * The Regents of the University of Michigan
   6  * ALL RIGHTS RESERVED
   7  *
   8  * Permission is granted to use, copy, create derivative works
   9  * and redistribute this software and such derivative works
  10  * for any purpose, so long as the name of The University of
  11  * Michigan is not used in any advertising or publicity
  12  * pertaining to the use of distribution of this software
  13  * without specific, written prior authorization.  If the
  14  * above copyright notice or any other identification of the
  15  * University of Michigan is included in any copy of any
  16  * portion of this software, then the disclaimer below must
  17  * also be included.
  18  *
  19  * THIS SOFTWARE IS PROVIDED AS IS, WITHOUT REPRESENTATION
  20  * FROM THE UNIVERSITY OF MICHIGAN AS TO ITS FITNESS FOR ANY
  21  * PURPOSE, AND WITHOUT WARRANTY BY THE UNIVERSITY OF
  22  * MICHIGAN OF ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING
  23  * WITHOUT LIMITATION THE IMPLIED WARRANTIES OF
  24  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE
  25  * REGENTS OF THE UNIVERSITY OF MICHIGAN SHALL NOT BE LIABLE
  26  * FOR ANY DAMAGES, INCLUDING SPECIAL, INDIRECT, INCIDENTAL, OR
  27  * CONSEQUENTIAL DAMAGES, WITH RESPECT TO ANY CLAIM ARISING
  28  * OUT OF OR IN CONNECTION WITH THE USE OF THE SOFTWARE, EVEN
  29  * IF IT HAS BEEN OR IS HEREAFTER ADVISED OF THE POSSIBILITY OF
  30  * SUCH DAMAGES.
  31  */
  32
  33 /* Derived from various:
  34  *      Copyright (c) 2006 Herbert Xu <herbert@gondor.apana.org.au>
  35  */
  36
  37 /*
  38  * This is the Cipher Text Stealing mode as described by
  39  * Section 8 of rfc2040 and referenced by rfc3962.
  40  * rfc3962 includes errata information in its Appendix A.
  41  */
  42
  43 #include <crypto/internal/skcipher.h>
  44 #include <linux/err.h>
  45 #include <linux/init.h>
  46 #include <linux/kernel.h>
  47 #include <linux/log2.h>
  48 #include <linux/module.h>
  49 #include <linux/scatterlist.h>
  50 #include <crypto/scatterwalk.h>
  51 #include <linux/slab.h>
  52
  53 struct crypto_cts_ctx {
  54         struct crypto_skcipher *child;
  55 };
  56
  57 struct crypto_cts_reqctx {
  58         struct scatterlist sg[2];
  59         unsigned offset;
  60         struct skcipher_request subreq;
  61 };
  62
  63 static inline u8 *crypto_cts_reqctx_space(struct skcipher_request *req)
  64 {
  65         struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
  66         struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
  67         struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
  68         struct crypto_skcipher *child = ctx->child;
  69
  70         return PTR_ALIGN((u8 *)(rctx + 1) + crypto_skcipher_reqsize(child),
  71                          crypto_skcipher_alignmask(tfm) + 1);
  72 }
  73
  74 static int crypto_cts_setkey(struct crypto_skcipher *parent, const u8 *key,
  75                              unsigned int keylen)
  76 {
  77         struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(parent);
  78         struct crypto_skcipher *child = ctx->child;
  79         int err;
  80
  81         crypto_skcipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
  82         crypto_skcipher_set_flags(child, crypto_skcipher_get_flags(parent) &
  83                                          CRYPTO_TFM_REQ_MASK);
  84         err = crypto_skcipher_setkey(child, key, keylen);
  85         crypto_skcipher_set_flags(parent, crypto_skcipher_get_flags(child) &
  86                                           CRYPTO_TFM_RES_MASK);
  87         return err;
  88 }
  89
  90 static void cts_cbc_crypt_done(struct crypto_async_request *areq, int err)
  91 {
  92         struct skcipher_request *req = areq->data;
  93
  94         if (err == -EINPROGRESS)
  95                 return;
  96
  97         skcipher_request_complete(req, err);
  98 }
  99
 100 static int cts_cbc_encrypt(struct skcipher_request *req)
 101 {
 102         struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
 103         struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 104         struct skcipher_request *subreq = &rctx->subreq;
 105         int bsize = crypto_skcipher_blocksize(tfm);
 106         u8 d[bsize * 2] __attribute__ ((aligned(__alignof__(u32))));
 107         struct scatterlist *sg;
 108         unsigned int offset;
 109         int lastn;
 110
 111         offset = rctx->offset;
 112         lastn = req->cryptlen - offset;
 113
 114         sg = scatterwalk_ffwd(rctx->sg, req->dst, offset - bsize);
 115         scatterwalk_map_and_copy(d + bsize, sg, 0, bsize, 0);
 116
 117         memset(d, 0, bsize);
 118         scatterwalk_map_and_copy(d, req->src, offset, lastn, 0);
 119
 120         scatterwalk_map_and_copy(d, sg, 0, bsize + lastn, 1);
 121         memzero_explicit(d, sizeof(d));
 122
 123         skcipher_request_set_callback(subreq, req->base.flags &
 124                                               CRYPTO_TFM_REQ_MAY_BACKLOG,
 125                                       cts_cbc_crypt_done, req);
 126         skcipher_request_set_crypt(subreq, sg, sg, bsize, req->iv);
 127         return crypto_skcipher_encrypt(subreq);
 128 }
 129
 130 static void crypto_cts_encrypt_done(struct crypto_async_request *areq, int err)
 131 {
 132         struct skcipher_request *req = areq->data;
 133
 134         if (err)
 135                 goto out;
 136
 137         err = cts_cbc_encrypt(req);
 138         if (err == -EINPROGRESS ||
 139             (err == -EBUSY && req->base.flags & CRYPTO_TFM_REQ_MAY_BACKLOG))
 140                 return;
 141
 142 out:
 143         skcipher_request_complete(req, err);
 144 }
 145
 146 static int crypto_cts_encrypt(struct skcipher_request *req)
 147 {
 148         struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 149         struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
 150         struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
 151         struct skcipher_request *subreq = &rctx->subreq;
 152         int bsize = crypto_skcipher_blocksize(tfm);
 153         unsigned int nbytes = req->cryptlen;
 154         int cbc_blocks = (nbytes + bsize - 1) / bsize - 1;
 155         unsigned int offset;
 156
 157         skcipher_request_set_tfm(subreq, ctx->child);
 158
 159         if (cbc_blocks <= 0) {
 160                 skcipher_request_set_callback(subreq, req->base.flags,
 161                                               req->base.complete,
 162                                               req->base.data);
 163                 skcipher_request_set_crypt(subreq, req->src, req->dst, nbytes,
 164                                            req->iv);
 165                 return crypto_skcipher_encrypt(subreq);
 166         }
 167
 168         offset = cbc_blocks * bsize;
 169         rctx->offset = offset;
 170
 171         skcipher_request_set_callback(subreq, req->base.flags,
 172                                       crypto_cts_encrypt_done, req);
 173         skcipher_request_set_crypt(subreq, req->src, req->dst,
 174                                    offset, req->iv);
 175
 176         return crypto_skcipher_encrypt(subreq) ?:
 177                cts_cbc_encrypt(req);
 178 }
 179
 180 static int cts_cbc_decrypt(struct skcipher_request *req)
 181 {
 182         struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
 183         struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 184         struct skcipher_request *subreq = &rctx->subreq;
 185         int bsize = crypto_skcipher_blocksize(tfm);
 186         u8 d[bsize * 2] __attribute__ ((aligned(__alignof__(u32))));
 187         struct scatterlist *sg;
 188         unsigned int offset;
 189         u8 *space;
 190         int lastn;
 191
 192         offset = rctx->offset;
 193         lastn = req->cryptlen - offset;
 194
 195         sg = scatterwalk_ffwd(rctx->sg, req->dst, offset - bsize);
 196
 197         /* 1. Decrypt Cn-1 (s) to create Dn */
 198         scatterwalk_map_and_copy(d + bsize, sg, 0, bsize, 0);
 199         space = crypto_cts_reqctx_space(req);
 200         crypto_xor(d + bsize, space, bsize);
 201         /* 2. Pad Cn with zeros at the end to create C of length BB */
 202         memset(d, 0, bsize);
 203         scatterwalk_map_and_copy(d, req->src, offset, lastn, 0);
 204         /* 3. Exclusive-or Dn with C to create Xn */
 205         /* 4. Select the first Ln bytes of Xn to create Pn */
 206         crypto_xor(d + bsize, d, lastn);
 207
 208         /* 5. Append the tail (BB - Ln) bytes of Xn to Cn to create En */
 209         memcpy(d + lastn, d + bsize + lastn, bsize - lastn);
 210         /* 6. Decrypt En to create Pn-1 */
 211
 212         scatterwalk_map_and_copy(d, sg, 0, bsize + lastn, 1);
 213         memzero_explicit(d, sizeof(d));
 214
 215         skcipher_request_set_callback(subreq, req->base.flags &
 216                                               CRYPTO_TFM_REQ_MAY_BACKLOG,
 217                                       cts_cbc_crypt_done, req);
 218
 219         skcipher_request_set_crypt(subreq, sg, sg, bsize, space);
 220         return crypto_skcipher_decrypt(subreq);
 221 }
 222
 223 static void crypto_cts_decrypt_done(struct crypto_async_request *areq, int err)
 224 {
 225         struct skcipher_request *req = areq->data;
 226
 227         if (err)
 228                 goto out;
 229
 230         err = cts_cbc_decrypt(req);
 231         if (err == -EINPROGRESS ||
 232             (err == -EBUSY && req->base.flags & CRYPTO_TFM_REQ_MAY_BACKLOG))
 233                 return;
 234
 235 out:
 236         skcipher_request_complete(req, err);
 237 }
 238
 239 static int crypto_cts_decrypt(struct skcipher_request *req)
 240 {
 241         struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 242         struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
 243         struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
 244         struct skcipher_request *subreq = &rctx->subreq;
 245         int bsize = crypto_skcipher_blocksize(tfm);
 246         unsigned int nbytes = req->cryptlen;
 247         int cbc_blocks = (nbytes + bsize - 1) / bsize - 1;
 248         unsigned int offset;
 249         u8 *space;
 250
 251         skcipher_request_set_tfm(subreq, ctx->child);
 252
 253         if (cbc_blocks <= 0) {
 254                 skcipher_request_set_callback(subreq, req->base.flags,
 255                                               req->base.complete,
 256                                               req->base.data);
 257                 skcipher_request_set_crypt(subreq, req->src, req->dst, nbytes,
 258                                            req->iv);
 259                 return crypto_skcipher_decrypt(subreq);
 260         }
 261
 262         skcipher_request_set_callback(subreq, req->base.flags,
 263                                       crypto_cts_decrypt_done, req);
 264
 265         space = crypto_cts_reqctx_space(req);
 266
 267         offset = cbc_blocks * bsize;
 268         rctx->offset = offset;
 269
 270         if (cbc_blocks <= 1)
 271                 memcpy(space, req->iv, bsize);
 272         else
 273                 scatterwalk_map_and_copy(space, req->src, offset - 2 * bsize,
 274                                          bsize, 0);
 275
 276         skcipher_request_set_crypt(subreq, req->src, req->dst,
 277                                    offset, req->iv);
 278
 279         return crypto_skcipher_decrypt(subreq) ?:
 280                cts_cbc_decrypt(req);
 281 }
 282
 283 static int crypto_cts_init_tfm(struct crypto_skcipher *tfm)
 284 {
 285         struct skcipher_instance *inst = skcipher_alg_instance(tfm);
 286         struct crypto_skcipher_spawn *spawn = skcipher_instance_ctx(inst);
 287         struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
 288         struct crypto_skcipher *cipher;
 289         unsigned reqsize;
 290         unsigned bsize;
 291         unsigned align;
 292
 293         cipher = crypto_spawn_skcipher(spawn);
 294         if (IS_ERR(cipher))
 295                 return PTR_ERR(cipher);
 296
 297         ctx->child = cipher;
 298
 299         align = crypto_skcipher_alignmask(tfm);
 300         bsize = crypto_skcipher_blocksize(cipher);
 301         reqsize = ALIGN(sizeof(struct crypto_cts_reqctx) +
 302                         crypto_skcipher_reqsize(cipher),
 303                         crypto_tfm_ctx_alignment()) +
 304                   (align & ~(crypto_tfm_ctx_alignment() - 1)) + bsize;
 305
 306         crypto_skcipher_set_reqsize(tfm, reqsize);
 307
 308         return 0;
 309 }
 310
 311 static void crypto_cts_exit_tfm(struct crypto_skcipher *tfm)
 312 {
 313         struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
 314
 315         crypto_free_skcipher(ctx->child);
 316 }
 317
 318 static void crypto_cts_free(struct skcipher_instance *inst)
 319 {
 320         crypto_drop_skcipher(skcipher_instance_ctx(inst));
 321         kfree(inst);
 322 }
 323
 324 static int crypto_cts_create(struct crypto_template *tmpl, struct rtattr **tb)
 325 {
 326         struct crypto_skcipher_spawn *spawn;
 327         struct skcipher_instance *inst;
 328         struct crypto_attr_type *algt;
 329         struct skcipher_alg *alg;
 330         const char *cipher_name;
 331         int err;
 332
 333         algt = crypto_get_attr_type(tb);
 334         if (IS_ERR(algt))
 335                 return PTR_ERR(algt);
 336
 337         if ((algt->type ^ CRYPTO_ALG_TYPE_SKCIPHER) & algt->mask)
 338                 return -EINVAL;
 339
 340         cipher_name = crypto_attr_alg_name(tb[1]);
 341         if (IS_ERR(cipher_name))
 342                 return PTR_ERR(cipher_name);
 343
 344         inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL);
 345         if (!inst)
 346                 return -ENOMEM;
 347
 348         spawn = skcipher_instance_ctx(inst);
 349
 350         crypto_set_skcipher_spawn(spawn, skcipher_crypto_instance(inst));
 351         err = crypto_grab_skcipher(spawn, cipher_name, 0,
 352                                    crypto_requires_sync(algt->type,
 353                                                         algt->mask));
 354         if (err)
 355                 goto err_free_inst;
 356
 357         alg = crypto_spawn_skcipher_alg(spawn);
 358
 359         err = -EINVAL;
 360         if (crypto_skcipher_alg_ivsize(alg) != alg->base.cra_blocksize)
 361                 goto err_drop_spawn;
 362
 363         if (strncmp(alg->base.cra_name, "cbc(", 4))
 364                 goto err_drop_spawn;
 365
 366         err = crypto_inst_setname(skcipher_crypto_instance(inst), "cts",
 367                                   &alg->base);
 368         if (err)
 369                 goto err_drop_spawn;
 370
 371         inst->alg.base.cra_flags = alg->base.cra_flags & CRYPTO_ALG_ASYNC;
 372         inst->alg.base.cra_priority = alg->base.cra_priority;
 373         inst->alg.base.cra_blocksize = alg->base.cra_blocksize;
 374         inst->alg.base.cra_alignmask = alg->base.cra_alignmask;
 375
 376         /* We access the data as u32s when xoring. */
 377         inst->alg.base.cra_alignmask |= __alignof__(u32) - 1;
 378
 379         inst->alg.ivsize = alg->base.cra_blocksize;
 380         inst->alg.chunksize = crypto_skcipher_alg_chunksize(alg);
 381         inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(alg);
 382         inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(alg);
 383
 384         inst->alg.base.cra_ctxsize = sizeof(struct crypto_cts_ctx);
 385
 386         inst->alg.init = crypto_cts_init_tfm;
 387         inst->alg.exit = crypto_cts_exit_tfm;
 388
 389         inst->alg.setkey = crypto_cts_setkey;
 390         inst->alg.encrypt = crypto_cts_encrypt;
 391         inst->alg.decrypt = crypto_cts_decrypt;
 392
 393         inst->free = crypto_cts_free;
 394
 395         err = skcipher_register_instance(tmpl, inst);
 396         if (err)
 397                 goto err_drop_spawn;
 398
 399 out:
 400         return err;
 401
 402 err_drop_spawn:
 403         crypto_drop_skcipher(spawn);
 404 err_free_inst:
 405         kfree(inst);
 406         goto out;
 407 }
 408
 409 static struct crypto_template crypto_cts_tmpl = {
 410         .name = "cts",
 411         .create = crypto_cts_create,
 412         .module = THIS_MODULE,
 413 };
 414
 415 static int __init crypto_cts_module_init(void)
 416 {
 417         return crypto_register_template(&crypto_cts_tmpl);
 418 }
 419
 420 static void __exit crypto_cts_module_exit(void)
 421 {
 422         crypto_unregister_template(&crypto_cts_tmpl);
 423 }
 424
 425 module_init(crypto_cts_module_init);
 426 module_exit(crypto_cts_module_exit);
 427
 428 MODULE_LICENSE("Dual BSD/GPL");
 429 MODULE_DESCRIPTION("CTS-CBC CipherText Stealing for CBC");
 430 MODULE_ALIAS_CRYPTO("cts");