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/algapi.h>
  44 #include <crypto/internal/skcipher.h>
  45 #include <linux/err.h>
  46 #include <linux/init.h>
  47 #include <linux/kernel.h>
  48 #include <linux/log2.h>
  49 #include <linux/module.h>
  50 #include <linux/scatterlist.h>
  51 #include <crypto/scatterwalk.h>
  52 #include <linux/slab.h>
  53 #include <linux/compiler.h>
  54
  55 struct crypto_cts_ctx {
  56         struct crypto_skcipher *child;
  57 };
  58
  59 struct crypto_cts_reqctx {
  60         struct scatterlist sg[2];
  61         unsigned offset;
  62         struct skcipher_request subreq;
  63 };
  64
  65 static inline u8 *crypto_cts_reqctx_space(struct skcipher_request *req)
  66 {
  67         struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
  68         struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
  69         struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
  70         struct crypto_skcipher *child = ctx->child;
  71
  72         return PTR_ALIGN((u8 *)(rctx + 1) + crypto_skcipher_reqsize(child),
  73                          crypto_skcipher_alignmask(tfm) + 1);
  74 }
  75
  76 static int crypto_cts_setkey(struct crypto_skcipher *parent, const u8 *key,
  77                              unsigned int keylen)
  78 {
  79         struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(parent);
  80         struct crypto_skcipher *child = ctx->child;
  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         return crypto_skcipher_setkey(child, key, keylen);
  86 }
  87
  88 static void cts_cbc_crypt_done(struct crypto_async_request *areq, int err)
  89 {
  90         struct skcipher_request *req = areq->data;
  91
  92         if (err == -EINPROGRESS)
  93                 return;
  94
  95         skcipher_request_complete(req, err);
  96 }
  97
  98 static int cts_cbc_encrypt(struct skcipher_request *req)
  99 {
 100         struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
 101         struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 102         struct skcipher_request *subreq = &rctx->subreq;
 103         int bsize = crypto_skcipher_blocksize(tfm);
 104         u8 d[MAX_CIPHER_BLOCKSIZE * 2] __aligned(__alignof__(u32));
 105         struct scatterlist *sg;
 106         unsigned int offset;
 107         int lastn;
 108
 109         offset = rctx->offset;
 110         lastn = req->cryptlen - offset;
 111
 112         sg = scatterwalk_ffwd(rctx->sg, req->dst, offset - bsize);
 113         scatterwalk_map_and_copy(d + bsize, sg, 0, bsize, 0);
 114
 115         memset(d, 0, bsize);
 116         scatterwalk_map_and_copy(d, req->src, offset, lastn, 0);
 117
 118         scatterwalk_map_and_copy(d, sg, 0, bsize + lastn, 1);
 119         memzero_explicit(d, sizeof(d));
 120
 121         skcipher_request_set_callback(subreq, req->base.flags &
 122                                               CRYPTO_TFM_REQ_MAY_BACKLOG,
 123                                       cts_cbc_crypt_done, req);
 124         skcipher_request_set_crypt(subreq, sg, sg, bsize, req->iv);
 125         return crypto_skcipher_encrypt(subreq);
 126 }
 127
 128 static void crypto_cts_encrypt_done(struct crypto_async_request *areq, int err)
 129 {
 130         struct skcipher_request *req = areq->data;
 131
 132         if (err)
 133                 goto out;
 134
 135         err = cts_cbc_encrypt(req);
 136         if (err == -EINPROGRESS || err == -EBUSY)
 137                 return;
 138
 139 out:
 140         skcipher_request_complete(req, err);
 141 }
 142
 143 static int crypto_cts_encrypt(struct skcipher_request *req)
 144 {
 145         struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 146         struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
 147         struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
 148         struct skcipher_request *subreq = &rctx->subreq;
 149         int bsize = crypto_skcipher_blocksize(tfm);
 150         unsigned int nbytes = req->cryptlen;
 151         unsigned int offset;
 152
 153         skcipher_request_set_tfm(subreq, ctx->child);
 154
 155         if (nbytes < bsize)
 156                 return -EINVAL;
 157
 158         if (nbytes == bsize) {
 159                 skcipher_request_set_callback(subreq, req->base.flags,
 160                                               req->base.complete,
 161                                               req->base.data);
 162                 skcipher_request_set_crypt(subreq, req->src, req->dst, nbytes,
 163                                            req->iv);
 164                 return crypto_skcipher_encrypt(subreq);
 165         }
 166
 167         offset = rounddown(nbytes - 1, bsize);
 168         rctx->offset = offset;
 169
 170         skcipher_request_set_callback(subreq, req->base.flags,
 171                                       crypto_cts_encrypt_done, req);
 172         skcipher_request_set_crypt(subreq, req->src, req->dst,
 173                                    offset, req->iv);
 174
 175         return crypto_skcipher_encrypt(subreq) ?:
 176                cts_cbc_encrypt(req);
 177 }
 178
 179 static int cts_cbc_decrypt(struct skcipher_request *req)
 180 {
 181         struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
 182         struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 183         struct skcipher_request *subreq = &rctx->subreq;
 184         int bsize = crypto_skcipher_blocksize(tfm);
 185         u8 d[MAX_CIPHER_BLOCKSIZE * 2] __aligned(__alignof__(u32));
 186         struct scatterlist *sg;
 187         unsigned int offset;
 188         u8 *space;
 189         int lastn;
 190
 191         offset = rctx->offset;
 192         lastn = req->cryptlen - offset;
 193
 194         sg = scatterwalk_ffwd(rctx->sg, req->dst, offset - bsize);
 195
 196         /* 1. Decrypt Cn-1 (s) to create Dn */
 197         scatterwalk_map_and_copy(d + bsize, sg, 0, bsize, 0);
 198         space = crypto_cts_reqctx_space(req);
 199         crypto_xor(d + bsize, space, bsize);
 200         /* 2. Pad Cn with zeros at the end to create C of length BB */
 201         memset(d, 0, bsize);
 202         scatterwalk_map_and_copy(d, req->src, offset, lastn, 0);
 203         /* 3. Exclusive-or Dn with C to create Xn */
 204         /* 4. Select the first Ln bytes of Xn to create Pn */
 205         crypto_xor(d + bsize, d, lastn);
 206
 207         /* 5. Append the tail (BB - Ln) bytes of Xn to Cn to create En */
 208         memcpy(d + lastn, d + bsize + lastn, bsize - lastn);
 209         /* 6. Decrypt En to create Pn-1 */
 210
 211         scatterwalk_map_and_copy(d, sg, 0, bsize + lastn, 1);
 212         memzero_explicit(d, sizeof(d));
 213
 214         skcipher_request_set_callback(subreq, req->base.flags &
 215                                               CRYPTO_TFM_REQ_MAY_BACKLOG,
 216                                       cts_cbc_crypt_done, req);
 217
 218         skcipher_request_set_crypt(subreq, sg, sg, bsize, space);
 219         return crypto_skcipher_decrypt(subreq);
 220 }
 221
 222 static void crypto_cts_decrypt_done(struct crypto_async_request *areq, int err)
 223 {
 224         struct skcipher_request *req = areq->data;
 225
 226         if (err)
 227                 goto out;
 228
 229         err = cts_cbc_decrypt(req);
 230         if (err == -EINPROGRESS || err == -EBUSY)
 231                 return;
 232
 233 out:
 234         skcipher_request_complete(req, err);
 235 }
 236
 237 static int crypto_cts_decrypt(struct skcipher_request *req)
 238 {
 239         struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 240         struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
 241         struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
 242         struct skcipher_request *subreq = &rctx->subreq;
 243         int bsize = crypto_skcipher_blocksize(tfm);
 244         unsigned int nbytes = req->cryptlen;
 245         unsigned int offset;
 246         u8 *space;
 247
 248         skcipher_request_set_tfm(subreq, ctx->child);
 249
 250         if (nbytes < bsize)
 251                 return -EINVAL;
 252
 253         if (nbytes == bsize) {
 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 = rounddown(nbytes - 1, bsize);
 268         rctx->offset = offset;
 269
 270         if (offset <= bsize)
 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 skcipher_alg *alg;
 329         u32 mask;
 330         int err;
 331
 332         err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_SKCIPHER, &mask);
 333         if (err)
 334                 return err;
 335
 336         inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL);
 337         if (!inst)
 338                 return -ENOMEM;
 339
 340         spawn = skcipher_instance_ctx(inst);
 341
 342         err = crypto_grab_skcipher(spawn, skcipher_crypto_instance(inst),
 343                                    crypto_attr_alg_name(tb[1]), 0, mask);
 344         if (err)
 345                 goto err_free_inst;
 346
 347         alg = crypto_spawn_skcipher_alg(spawn);
 348
 349         err = -EINVAL;
 350         if (crypto_skcipher_alg_ivsize(alg) != alg->base.cra_blocksize)
 351                 goto err_free_inst;
 352
 353         if (strncmp(alg->base.cra_name, "cbc(", 4))
 354                 goto err_free_inst;
 355
 356         err = crypto_inst_setname(skcipher_crypto_instance(inst), "cts",
 357                                   &alg->base);
 358         if (err)
 359                 goto err_free_inst;
 360
 361         inst->alg.base.cra_priority = alg->base.cra_priority;
 362         inst->alg.base.cra_blocksize = alg->base.cra_blocksize;
 363         inst->alg.base.cra_alignmask = alg->base.cra_alignmask;
 364
 365         inst->alg.ivsize = alg->base.cra_blocksize;
 366         inst->alg.chunksize = crypto_skcipher_alg_chunksize(alg);
 367         inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(alg);
 368         inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(alg);
 369
 370         inst->alg.base.cra_ctxsize = sizeof(struct crypto_cts_ctx);
 371
 372         inst->alg.init = crypto_cts_init_tfm;
 373         inst->alg.exit = crypto_cts_exit_tfm;
 374
 375         inst->alg.setkey = crypto_cts_setkey;
 376         inst->alg.encrypt = crypto_cts_encrypt;
 377         inst->alg.decrypt = crypto_cts_decrypt;
 378
 379         inst->free = crypto_cts_free;
 380
 381         err = skcipher_register_instance(tmpl, inst);
 382         if (err) {
 383 err_free_inst:
 384                 crypto_cts_free(inst);
 385         }
 386         return err;
 387 }
 388
 389 static struct crypto_template crypto_cts_tmpl = {
 390         .name = "cts",
 391         .create = crypto_cts_create,
 392         .module = THIS_MODULE,
 393 };
 394
 395 static int __init crypto_cts_module_init(void)
 396 {
 397         return crypto_register_template(&crypto_cts_tmpl);
 398 }
 399
 400 static void __exit crypto_cts_module_exit(void)
 401 {
 402         crypto_unregister_template(&crypto_cts_tmpl);
 403 }
 404
 405 subsys_initcall(crypto_cts_module_init);
 406 module_exit(crypto_cts_module_exit);
 407
 408 MODULE_LICENSE("Dual BSD/GPL");
 409 MODULE_DESCRIPTION("CTS-CBC CipherText Stealing for CBC");
 410 MODULE_ALIAS_CRYPTO("cts");