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 #include <linux/compiler.h>
  53
  54 struct crypto_cts_ctx {
  55         struct crypto_skcipher *child;
  56 };
  57
  58 struct crypto_cts_reqctx {
  59         struct scatterlist sg[2];
  60         unsigned offset;
  61         struct skcipher_request subreq;
  62 };
  63
  64 static inline u8 *crypto_cts_reqctx_space(struct skcipher_request *req)
  65 {
  66         struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
  67         struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
  68         struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
  69         struct crypto_skcipher *child = ctx->child;
  70
  71         return PTR_ALIGN((u8 *)(rctx + 1) + crypto_skcipher_reqsize(child),
  72                          crypto_skcipher_alignmask(tfm) + 1);
  73 }
  74
  75 static int crypto_cts_setkey(struct crypto_skcipher *parent, const u8 *key,
  76                              unsigned int keylen)
  77 {
  78         struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(parent);
  79         struct crypto_skcipher *child = ctx->child;
  80         int err;
  81
  82         crypto_skcipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
  83         crypto_skcipher_set_flags(child, crypto_skcipher_get_flags(parent) &
  84                                          CRYPTO_TFM_REQ_MASK);
  85         err = crypto_skcipher_setkey(child, key, keylen);
  86         crypto_skcipher_set_flags(parent, crypto_skcipher_get_flags(child) &
  87                                           CRYPTO_TFM_RES_MASK);
  88         return err;
  89 }
  90
  91 static void cts_cbc_crypt_done(struct crypto_async_request *areq, int err)
  92 {
  93         struct skcipher_request *req = areq->data;
  94
  95         if (err == -EINPROGRESS)
  96                 return;
  97
  98         skcipher_request_complete(req, err);
  99 }
 100
 101 static int cts_cbc_encrypt(struct skcipher_request *req)
 102 {
 103         struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
 104         struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 105         struct skcipher_request *subreq = &rctx->subreq;
 106         int bsize = crypto_skcipher_blocksize(tfm);
 107         u8 d[bsize * 2] __aligned(__alignof__(u32));
 108         struct scatterlist *sg;
 109         unsigned int offset;
 110         int lastn;
 111
 112         offset = rctx->offset;
 113         lastn = req->cryptlen - offset;
 114
 115         sg = scatterwalk_ffwd(rctx->sg, req->dst, offset - bsize);
 116         scatterwalk_map_and_copy(d + bsize, sg, 0, bsize, 0);
 117
 118         memset(d, 0, bsize);
 119         scatterwalk_map_and_copy(d, req->src, offset, lastn, 0);
 120
 121         scatterwalk_map_and_copy(d, sg, 0, bsize + lastn, 1);
 122         memzero_explicit(d, sizeof(d));
 123
 124         skcipher_request_set_callback(subreq, req->base.flags &
 125                                               CRYPTO_TFM_REQ_MAY_BACKLOG,
 126                                       cts_cbc_crypt_done, req);
 127         skcipher_request_set_crypt(subreq, sg, sg, bsize, req->iv);
 128         return crypto_skcipher_encrypt(subreq);
 129 }
 130
 131 static void crypto_cts_encrypt_done(struct crypto_async_request *areq, int err)
 132 {
 133         struct skcipher_request *req = areq->data;
 134
 135         if (err)
 136                 goto out;
 137
 138         err = cts_cbc_encrypt(req);
 139         if (err == -EINPROGRESS || err == -EBUSY)
 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] __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 || err == -EBUSY)
 232                 return;
 233
 234 out:
 235         skcipher_request_complete(req, err);
 236 }
 237
 238 static int crypto_cts_decrypt(struct skcipher_request *req)
 239 {
 240         struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 241         struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
 242         struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
 243         struct skcipher_request *subreq = &rctx->subreq;
 244         int bsize = crypto_skcipher_blocksize(tfm);
 245         unsigned int nbytes = req->cryptlen;
 246         int cbc_blocks = (nbytes + bsize - 1) / bsize - 1;
 247         unsigned int offset;
 248         u8 *space;
 249
 250         skcipher_request_set_tfm(subreq, ctx->child);
 251
 252         if (cbc_blocks <= 0) {
 253                 skcipher_request_set_callback(subreq, req->base.flags,
 254                                               req->base.complete,
 255                                               req->base.data);
 256                 skcipher_request_set_crypt(subreq, req->src, req->dst, nbytes,
 257                                            req->iv);
 258                 return crypto_skcipher_decrypt(subreq);
 259         }
 260
 261         skcipher_request_set_callback(subreq, req->base.flags,
 262                                       crypto_cts_decrypt_done, req);
 263
 264         space = crypto_cts_reqctx_space(req);
 265
 266         offset = cbc_blocks * bsize;
 267         rctx->offset = offset;
 268
 269         if (cbc_blocks <= 1)
 270                 memcpy(space, req->iv, bsize);
 271         else
 272                 scatterwalk_map_and_copy(space, req->src, offset - 2 * bsize,
 273                                          bsize, 0);
 274
 275         skcipher_request_set_crypt(subreq, req->src, req->dst,
 276                                    offset, req->iv);
 277
 278         return crypto_skcipher_decrypt(subreq) ?:
 279                cts_cbc_decrypt(req);
 280 }
 281
 282 static int crypto_cts_init_tfm(struct crypto_skcipher *tfm)
 283 {
 284         struct skcipher_instance *inst = skcipher_alg_instance(tfm);
 285         struct crypto_skcipher_spawn *spawn = skcipher_instance_ctx(inst);
 286         struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
 287         struct crypto_skcipher *cipher;
 288         unsigned reqsize;
 289         unsigned bsize;
 290         unsigned align;
 291
 292         cipher = crypto_spawn_skcipher(spawn);
 293         if (IS_ERR(cipher))
 294                 return PTR_ERR(cipher);
 295
 296         ctx->child = cipher;
 297
 298         align = crypto_skcipher_alignmask(tfm);
 299         bsize = crypto_skcipher_blocksize(cipher);
 300         reqsize = ALIGN(sizeof(struct crypto_cts_reqctx) +
 301                         crypto_skcipher_reqsize(cipher),
 302                         crypto_tfm_ctx_alignment()) +
 303                   (align & ~(crypto_tfm_ctx_alignment() - 1)) + bsize;
 304
 305         crypto_skcipher_set_reqsize(tfm, reqsize);
 306
 307         return 0;
 308 }
 309
 310 static void crypto_cts_exit_tfm(struct crypto_skcipher *tfm)
 311 {
 312         struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
 313
 314         crypto_free_skcipher(ctx->child);
 315 }
 316
 317 static void crypto_cts_free(struct skcipher_instance *inst)
 318 {
 319         crypto_drop_skcipher(skcipher_instance_ctx(inst));
 320         kfree(inst);
 321 }
 322
 323 static int crypto_cts_create(struct crypto_template *tmpl, struct rtattr **tb)
 324 {
 325         struct crypto_skcipher_spawn *spawn;
 326         struct skcipher_instance *inst;
 327         struct crypto_attr_type *algt;
 328         struct skcipher_alg *alg;
 329         const char *cipher_name;
 330         int err;
 331
 332         algt = crypto_get_attr_type(tb);
 333         if (IS_ERR(algt))
 334                 return PTR_ERR(algt);
 335
 336         if ((algt->type ^ CRYPTO_ALG_TYPE_SKCIPHER) & algt->mask)
 337                 return -EINVAL;
 338
 339         cipher_name = crypto_attr_alg_name(tb[1]);
 340         if (IS_ERR(cipher_name))
 341                 return PTR_ERR(cipher_name);
 342
 343         inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL);
 344         if (!inst)
 345                 return -ENOMEM;
 346
 347         spawn = skcipher_instance_ctx(inst);
 348
 349         crypto_set_skcipher_spawn(spawn, skcipher_crypto_instance(inst));
 350         err = crypto_grab_skcipher(spawn, cipher_name, 0,
 351                                    crypto_requires_sync(algt->type,
 352                                                         algt->mask));
 353         if (err)
 354                 goto err_free_inst;
 355
 356         alg = crypto_spawn_skcipher_alg(spawn);
 357
 358         err = -EINVAL;
 359         if (crypto_skcipher_alg_ivsize(alg) != alg->base.cra_blocksize)
 360                 goto err_drop_spawn;
 361
 362         if (strncmp(alg->base.cra_name, "cbc(", 4))
 363                 goto err_drop_spawn;
 364
 365         err = crypto_inst_setname(skcipher_crypto_instance(inst), "cts",
 366                                   &alg->base);
 367         if (err)
 368                 goto err_drop_spawn;
 369
 370         inst->alg.base.cra_flags = alg->base.cra_flags & CRYPTO_ALG_ASYNC;
 371         inst->alg.base.cra_priority = alg->base.cra_priority;
 372         inst->alg.base.cra_blocksize = alg->base.cra_blocksize;
 373         inst->alg.base.cra_alignmask = alg->base.cra_alignmask;
 374
 375         inst->alg.ivsize = alg->base.cra_blocksize;
 376         inst->alg.chunksize = crypto_skcipher_alg_chunksize(alg);
 377         inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(alg);
 378         inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(alg);
 379
 380         inst->alg.base.cra_ctxsize = sizeof(struct crypto_cts_ctx);
 381
 382         inst->alg.init = crypto_cts_init_tfm;
 383         inst->alg.exit = crypto_cts_exit_tfm;
 384
 385         inst->alg.setkey = crypto_cts_setkey;
 386         inst->alg.encrypt = crypto_cts_encrypt;
 387         inst->alg.decrypt = crypto_cts_decrypt;
 388
 389         inst->free = crypto_cts_free;
 390
 391         err = skcipher_register_instance(tmpl, inst);
 392         if (err)
 393                 goto err_drop_spawn;
 394
 395 out:
 396         return err;
 397
 398 err_drop_spawn:
 399         crypto_drop_skcipher(spawn);
 400 err_free_inst:
 401         kfree(inst);
 402         goto out;
 403 }
 404
 405 static struct crypto_template crypto_cts_tmpl = {
 406         .name = "cts",
 407         .create = crypto_cts_create,
 408         .module = THIS_MODULE,
 409 };
 410
 411 static int __init crypto_cts_module_init(void)
 412 {
 413         return crypto_register_template(&crypto_cts_tmpl);
 414 }
 415
 416 static void __exit crypto_cts_module_exit(void)
 417 {
 418         crypto_unregister_template(&crypto_cts_tmpl);
 419 }
 420
 421 module_init(crypto_cts_module_init);
 422 module_exit(crypto_cts_module_exit);
 423
 424 MODULE_LICENSE("Dual BSD/GPL");
 425 MODULE_DESCRIPTION("CTS-CBC CipherText Stealing for CBC");
 426 MODULE_ALIAS_CRYPTO("cts");