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 ||
 140             (err == -EBUSY && req->base.flags & CRYPTO_TFM_REQ_MAY_BACKLOG))
 141                 return;
 142
 143 out:
 144         skcipher_request_complete(req, err);
 145 }
 146
 147 static int crypto_cts_encrypt(struct skcipher_request *req)
 148 {
 149         struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 150         struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
 151         struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
 152         struct skcipher_request *subreq = &rctx->subreq;
 153         int bsize = crypto_skcipher_blocksize(tfm);
 154         unsigned int nbytes = req->cryptlen;
 155         int cbc_blocks = (nbytes + bsize - 1) / bsize - 1;
 156         unsigned int offset;
 157
 158         skcipher_request_set_tfm(subreq, ctx->child);
 159
 160         if (cbc_blocks <= 0) {
 161                 skcipher_request_set_callback(subreq, req->base.flags,
 162                                               req->base.complete,
 163                                               req->base.data);
 164                 skcipher_request_set_crypt(subreq, req->src, req->dst, nbytes,
 165                                            req->iv);
 166                 return crypto_skcipher_encrypt(subreq);
 167         }
 168
 169         offset = cbc_blocks * bsize;
 170         rctx->offset = offset;
 171
 172         skcipher_request_set_callback(subreq, req->base.flags,
 173                                       crypto_cts_encrypt_done, req);
 174         skcipher_request_set_crypt(subreq, req->src, req->dst,
 175                                    offset, req->iv);
 176
 177         return crypto_skcipher_encrypt(subreq) ?:
 178                cts_cbc_encrypt(req);
 179 }
 180
 181 static int cts_cbc_decrypt(struct skcipher_request *req)
 182 {
 183         struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
 184         struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 185         struct skcipher_request *subreq = &rctx->subreq;
 186         int bsize = crypto_skcipher_blocksize(tfm);
 187         u8 d[bsize * 2] __aligned(__alignof__(u32));
 188         struct scatterlist *sg;
 189         unsigned int offset;
 190         u8 *space;
 191         int lastn;
 192
 193         offset = rctx->offset;
 194         lastn = req->cryptlen - offset;
 195
 196         sg = scatterwalk_ffwd(rctx->sg, req->dst, offset - bsize);
 197
 198         /* 1. Decrypt Cn-1 (s) to create Dn */
 199         scatterwalk_map_and_copy(d + bsize, sg, 0, bsize, 0);
 200         space = crypto_cts_reqctx_space(req);
 201         crypto_xor(d + bsize, space, bsize);
 202         /* 2. Pad Cn with zeros at the end to create C of length BB */
 203         memset(d, 0, bsize);
 204         scatterwalk_map_and_copy(d, req->src, offset, lastn, 0);
 205         /* 3. Exclusive-or Dn with C to create Xn */
 206         /* 4. Select the first Ln bytes of Xn to create Pn */
 207         crypto_xor(d + bsize, d, lastn);
 208
 209         /* 5. Append the tail (BB - Ln) bytes of Xn to Cn to create En */
 210         memcpy(d + lastn, d + bsize + lastn, bsize - lastn);
 211         /* 6. Decrypt En to create Pn-1 */
 212
 213         scatterwalk_map_and_copy(d, sg, 0, bsize + lastn, 1);
 214         memzero_explicit(d, sizeof(d));
 215
 216         skcipher_request_set_callback(subreq, req->base.flags &
 217                                               CRYPTO_TFM_REQ_MAY_BACKLOG,
 218                                       cts_cbc_crypt_done, req);
 219
 220         skcipher_request_set_crypt(subreq, sg, sg, bsize, space);
 221         return crypto_skcipher_decrypt(subreq);
 222 }
 223
 224 static void crypto_cts_decrypt_done(struct crypto_async_request *areq, int err)
 225 {
 226         struct skcipher_request *req = areq->data;
 227
 228         if (err)
 229                 goto out;
 230
 231         err = cts_cbc_decrypt(req);
 232         if (err == -EINPROGRESS ||
 233             (err == -EBUSY && req->base.flags & CRYPTO_TFM_REQ_MAY_BACKLOG))
 234                 return;
 235
 236 out:
 237         skcipher_request_complete(req, err);
 238 }
 239
 240 static int crypto_cts_decrypt(struct skcipher_request *req)
 241 {
 242         struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 243         struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
 244         struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
 245         struct skcipher_request *subreq = &rctx->subreq;
 246         int bsize = crypto_skcipher_blocksize(tfm);
 247         unsigned int nbytes = req->cryptlen;
 248         int cbc_blocks = (nbytes + bsize - 1) / bsize - 1;
 249         unsigned int offset;
 250         u8 *space;
 251
 252         skcipher_request_set_tfm(subreq, ctx->child);
 253
 254         if (cbc_blocks <= 0) {
 255                 skcipher_request_set_callback(subreq, req->base.flags,
 256                                               req->base.complete,
 257                                               req->base.data);
 258                 skcipher_request_set_crypt(subreq, req->src, req->dst, nbytes,
 259                                            req->iv);
 260                 return crypto_skcipher_decrypt(subreq);
 261         }
 262
 263         skcipher_request_set_callback(subreq, req->base.flags,
 264                                       crypto_cts_decrypt_done, req);
 265
 266         space = crypto_cts_reqctx_space(req);
 267
 268         offset = cbc_blocks * bsize;
 269         rctx->offset = offset;
 270
 271         if (cbc_blocks <= 1)
 272                 memcpy(space, req->iv, bsize);
 273         else
 274                 scatterwalk_map_and_copy(space, req->src, offset - 2 * bsize,
 275                                          bsize, 0);
 276
 277         skcipher_request_set_crypt(subreq, req->src, req->dst,
 278                                    offset, req->iv);
 279
 280         return crypto_skcipher_decrypt(subreq) ?:
 281                cts_cbc_decrypt(req);
 282 }
 283
 284 static int crypto_cts_init_tfm(struct crypto_skcipher *tfm)
 285 {
 286         struct skcipher_instance *inst = skcipher_alg_instance(tfm);
 287         struct crypto_skcipher_spawn *spawn = skcipher_instance_ctx(inst);
 288         struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
 289         struct crypto_skcipher *cipher;
 290         unsigned reqsize;
 291         unsigned bsize;
 292         unsigned align;
 293
 294         cipher = crypto_spawn_skcipher(spawn);
 295         if (IS_ERR(cipher))
 296                 return PTR_ERR(cipher);
 297
 298         ctx->child = cipher;
 299
 300         align = crypto_skcipher_alignmask(tfm);
 301         bsize = crypto_skcipher_blocksize(cipher);
 302         reqsize = ALIGN(sizeof(struct crypto_cts_reqctx) +
 303                         crypto_skcipher_reqsize(cipher),
 304                         crypto_tfm_ctx_alignment()) +
 305                   (align & ~(crypto_tfm_ctx_alignment() - 1)) + bsize;
 306
 307         crypto_skcipher_set_reqsize(tfm, reqsize);
 308
 309         return 0;
 310 }
 311
 312 static void crypto_cts_exit_tfm(struct crypto_skcipher *tfm)
 313 {
 314         struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
 315
 316         crypto_free_skcipher(ctx->child);
 317 }
 318
 319 static void crypto_cts_free(struct skcipher_instance *inst)
 320 {
 321         crypto_drop_skcipher(skcipher_instance_ctx(inst));
 322         kfree(inst);
 323 }
 324
 325 static int crypto_cts_create(struct crypto_template *tmpl, struct rtattr **tb)
 326 {
 327         struct crypto_skcipher_spawn *spawn;
 328         struct skcipher_instance *inst;
 329         struct crypto_attr_type *algt;
 330         struct skcipher_alg *alg;
 331         const char *cipher_name;
 332         int err;
 333
 334         algt = crypto_get_attr_type(tb);
 335         if (IS_ERR(algt))
 336                 return PTR_ERR(algt);
 337
 338         if ((algt->type ^ CRYPTO_ALG_TYPE_SKCIPHER) & algt->mask)
 339                 return -EINVAL;
 340
 341         cipher_name = crypto_attr_alg_name(tb[1]);
 342         if (IS_ERR(cipher_name))
 343                 return PTR_ERR(cipher_name);
 344
 345         inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL);
 346         if (!inst)
 347                 return -ENOMEM;
 348
 349         spawn = skcipher_instance_ctx(inst);
 350
 351         crypto_set_skcipher_spawn(spawn, skcipher_crypto_instance(inst));
 352         err = crypto_grab_skcipher(spawn, cipher_name, 0,
 353                                    crypto_requires_sync(algt->type,
 354                                                         algt->mask));
 355         if (err)
 356                 goto err_free_inst;
 357
 358         alg = crypto_spawn_skcipher_alg(spawn);
 359
 360         err = -EINVAL;
 361         if (crypto_skcipher_alg_ivsize(alg) != alg->base.cra_blocksize)
 362                 goto err_drop_spawn;
 363
 364         if (strncmp(alg->base.cra_name, "cbc(", 4))
 365                 goto err_drop_spawn;
 366
 367         err = crypto_inst_setname(skcipher_crypto_instance(inst), "cts",
 368                                   &alg->base);
 369         if (err)
 370                 goto err_drop_spawn;
 371
 372         inst->alg.base.cra_flags = alg->base.cra_flags & CRYPTO_ALG_ASYNC;
 373         inst->alg.base.cra_priority = alg->base.cra_priority;
 374         inst->alg.base.cra_blocksize = alg->base.cra_blocksize;
 375         inst->alg.base.cra_alignmask = alg->base.cra_alignmask;
 376
 377         inst->alg.ivsize = alg->base.cra_blocksize;
 378         inst->alg.chunksize = crypto_skcipher_alg_chunksize(alg);
 379         inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(alg);
 380         inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(alg);
 381
 382         inst->alg.base.cra_ctxsize = sizeof(struct crypto_cts_ctx);
 383
 384         inst->alg.init = crypto_cts_init_tfm;
 385         inst->alg.exit = crypto_cts_exit_tfm;
 386
 387         inst->alg.setkey = crypto_cts_setkey;
 388         inst->alg.encrypt = crypto_cts_encrypt;
 389         inst->alg.decrypt = crypto_cts_decrypt;
 390
 391         inst->free = crypto_cts_free;
 392
 393         err = skcipher_register_instance(tmpl, inst);
 394         if (err)
 395                 goto err_drop_spawn;
 396
 397 out:
 398         return err;
 399
 400 err_drop_spawn:
 401         crypto_drop_skcipher(spawn);
 402 err_free_inst:
 403         kfree(inst);
 404         goto out;
 405 }
 406
 407 static struct crypto_template crypto_cts_tmpl = {
 408         .name = "cts",
 409         .create = crypto_cts_create,
 410         .module = THIS_MODULE,
 411 };
 412
 413 static int __init crypto_cts_module_init(void)
 414 {
 415         return crypto_register_template(&crypto_cts_tmpl);
 416 }
 417
 418 static void __exit crypto_cts_module_exit(void)
 419 {
 420         crypto_unregister_template(&crypto_cts_tmpl);
 421 }
 422
 423 module_init(crypto_cts_module_init);
 424 module_exit(crypto_cts_module_exit);
 425
 426 MODULE_LICENSE("Dual BSD/GPL");
 427 MODULE_DESCRIPTION("CTS-CBC CipherText Stealing for CBC");
 428 MODULE_ALIAS_CRYPTO("cts");