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         int err;
  82
  83         crypto_skcipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
  84         crypto_skcipher_set_flags(child, crypto_skcipher_get_flags(parent) &
  85                                          CRYPTO_TFM_REQ_MASK);
  86         err = crypto_skcipher_setkey(child, key, keylen);
  87         crypto_skcipher_set_flags(parent, crypto_skcipher_get_flags(child) &
  88                                           CRYPTO_TFM_RES_MASK);
  89         return err;
  90 }
  91
  92 static void cts_cbc_crypt_done(struct crypto_async_request *areq, int err)
  93 {
  94         struct skcipher_request *req = areq->data;
  95
  96         if (err == -EINPROGRESS)
  97                 return;
  98
  99         skcipher_request_complete(req, err);
 100 }
 101
 102 static int cts_cbc_encrypt(struct skcipher_request *req)
 103 {
 104         struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
 105         struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 106         struct skcipher_request *subreq = &rctx->subreq;
 107         int bsize = crypto_skcipher_blocksize(tfm);
 108         u8 d[MAX_CIPHER_BLOCKSIZE * 2] __aligned(__alignof__(u32));
 109         struct scatterlist *sg;
 110         unsigned int offset;
 111         int lastn;
 112
 113         offset = rctx->offset;
 114         lastn = req->cryptlen - offset;
 115
 116         sg = scatterwalk_ffwd(rctx->sg, req->dst, offset - bsize);
 117         scatterwalk_map_and_copy(d + bsize, sg, 0, bsize, 0);
 118
 119         memset(d, 0, bsize);
 120         scatterwalk_map_and_copy(d, req->src, offset, lastn, 0);
 121
 122         scatterwalk_map_and_copy(d, sg, 0, bsize + lastn, 1);
 123         memzero_explicit(d, sizeof(d));
 124
 125         skcipher_request_set_callback(subreq, req->base.flags &
 126                                               CRYPTO_TFM_REQ_MAY_BACKLOG,
 127                                       cts_cbc_crypt_done, req);
 128         skcipher_request_set_crypt(subreq, sg, sg, bsize, req->iv);
 129         return crypto_skcipher_encrypt(subreq);
 130 }
 131
 132 static void crypto_cts_encrypt_done(struct crypto_async_request *areq, int err)
 133 {
 134         struct skcipher_request *req = areq->data;
 135
 136         if (err)
 137                 goto out;
 138
 139         err = cts_cbc_encrypt(req);
 140         if (err == -EINPROGRESS || err == -EBUSY)
 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         unsigned int offset;
 156
 157         skcipher_request_set_tfm(subreq, ctx->child);
 158
 159         if (nbytes < bsize)
 160                 return -EINVAL;
 161
 162         if (nbytes == bsize) {
 163                 skcipher_request_set_callback(subreq, req->base.flags,
 164                                               req->base.complete,
 165                                               req->base.data);
 166                 skcipher_request_set_crypt(subreq, req->src, req->dst, nbytes,
 167                                            req->iv);
 168                 return crypto_skcipher_encrypt(subreq);
 169         }
 170
 171         offset = rounddown(nbytes - 1, bsize);
 172         rctx->offset = offset;
 173
 174         skcipher_request_set_callback(subreq, req->base.flags,
 175                                       crypto_cts_encrypt_done, req);
 176         skcipher_request_set_crypt(subreq, req->src, req->dst,
 177                                    offset, req->iv);
 178
 179         return crypto_skcipher_encrypt(subreq) ?:
 180                cts_cbc_encrypt(req);
 181 }
 182
 183 static int cts_cbc_decrypt(struct skcipher_request *req)
 184 {
 185         struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
 186         struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 187         struct skcipher_request *subreq = &rctx->subreq;
 188         int bsize = crypto_skcipher_blocksize(tfm);
 189         u8 d[MAX_CIPHER_BLOCKSIZE * 2] __aligned(__alignof__(u32));
 190         struct scatterlist *sg;
 191         unsigned int offset;
 192         u8 *space;
 193         int lastn;
 194
 195         offset = rctx->offset;
 196         lastn = req->cryptlen - offset;
 197
 198         sg = scatterwalk_ffwd(rctx->sg, req->dst, offset - bsize);
 199
 200         /* 1. Decrypt Cn-1 (s) to create Dn */
 201         scatterwalk_map_and_copy(d + bsize, sg, 0, bsize, 0);
 202         space = crypto_cts_reqctx_space(req);
 203         crypto_xor(d + bsize, space, bsize);
 204         /* 2. Pad Cn with zeros at the end to create C of length BB */
 205         memset(d, 0, bsize);
 206         scatterwalk_map_and_copy(d, req->src, offset, lastn, 0);
 207         /* 3. Exclusive-or Dn with C to create Xn */
 208         /* 4. Select the first Ln bytes of Xn to create Pn */
 209         crypto_xor(d + bsize, d, lastn);
 210
 211         /* 5. Append the tail (BB - Ln) bytes of Xn to Cn to create En */
 212         memcpy(d + lastn, d + bsize + lastn, bsize - lastn);
 213         /* 6. Decrypt En to create Pn-1 */
 214
 215         scatterwalk_map_and_copy(d, sg, 0, bsize + lastn, 1);
 216         memzero_explicit(d, sizeof(d));
 217
 218         skcipher_request_set_callback(subreq, req->base.flags &
 219                                               CRYPTO_TFM_REQ_MAY_BACKLOG,
 220                                       cts_cbc_crypt_done, req);
 221
 222         skcipher_request_set_crypt(subreq, sg, sg, bsize, space);
 223         return crypto_skcipher_decrypt(subreq);
 224 }
 225
 226 static void crypto_cts_decrypt_done(struct crypto_async_request *areq, int err)
 227 {
 228         struct skcipher_request *req = areq->data;
 229
 230         if (err)
 231                 goto out;
 232
 233         err = cts_cbc_decrypt(req);
 234         if (err == -EINPROGRESS || err == -EBUSY)
 235                 return;
 236
 237 out:
 238         skcipher_request_complete(req, err);
 239 }
 240
 241 static int crypto_cts_decrypt(struct skcipher_request *req)
 242 {
 243         struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 244         struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
 245         struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
 246         struct skcipher_request *subreq = &rctx->subreq;
 247         int bsize = crypto_skcipher_blocksize(tfm);
 248         unsigned int nbytes = req->cryptlen;
 249         unsigned int offset;
 250         u8 *space;
 251
 252         skcipher_request_set_tfm(subreq, ctx->child);
 253
 254         if (nbytes < bsize)
 255                 return -EINVAL;
 256
 257         if (nbytes == bsize) {
 258                 skcipher_request_set_callback(subreq, req->base.flags,
 259                                               req->base.complete,
 260                                               req->base.data);
 261                 skcipher_request_set_crypt(subreq, req->src, req->dst, nbytes,
 262                                            req->iv);
 263                 return crypto_skcipher_decrypt(subreq);
 264         }
 265
 266         skcipher_request_set_callback(subreq, req->base.flags,
 267                                       crypto_cts_decrypt_done, req);
 268
 269         space = crypto_cts_reqctx_space(req);
 270
 271         offset = rounddown(nbytes - 1, bsize);
 272         rctx->offset = offset;
 273
 274         if (offset <= bsize)
 275                 memcpy(space, req->iv, bsize);
 276         else
 277                 scatterwalk_map_and_copy(space, req->src, offset - 2 * bsize,
 278                                          bsize, 0);
 279
 280         skcipher_request_set_crypt(subreq, req->src, req->dst,
 281                                    offset, req->iv);
 282
 283         return crypto_skcipher_decrypt(subreq) ?:
 284                cts_cbc_decrypt(req);
 285 }
 286
 287 static int crypto_cts_init_tfm(struct crypto_skcipher *tfm)
 288 {
 289         struct skcipher_instance *inst = skcipher_alg_instance(tfm);
 290         struct crypto_skcipher_spawn *spawn = skcipher_instance_ctx(inst);
 291         struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
 292         struct crypto_skcipher *cipher;
 293         unsigned reqsize;
 294         unsigned bsize;
 295         unsigned align;
 296
 297         cipher = crypto_spawn_skcipher(spawn);
 298         if (IS_ERR(cipher))
 299                 return PTR_ERR(cipher);
 300
 301         ctx->child = cipher;
 302
 303         align = crypto_skcipher_alignmask(tfm);
 304         bsize = crypto_skcipher_blocksize(cipher);
 305         reqsize = ALIGN(sizeof(struct crypto_cts_reqctx) +
 306                         crypto_skcipher_reqsize(cipher),
 307                         crypto_tfm_ctx_alignment()) +
 308                   (align & ~(crypto_tfm_ctx_alignment() - 1)) + bsize;
 309
 310         crypto_skcipher_set_reqsize(tfm, reqsize);
 311
 312         return 0;
 313 }
 314
 315 static void crypto_cts_exit_tfm(struct crypto_skcipher *tfm)
 316 {
 317         struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
 318
 319         crypto_free_skcipher(ctx->child);
 320 }
 321
 322 static void crypto_cts_free(struct skcipher_instance *inst)
 323 {
 324         crypto_drop_skcipher(skcipher_instance_ctx(inst));
 325         kfree(inst);
 326 }
 327
 328 static int crypto_cts_create(struct crypto_template *tmpl, struct rtattr **tb)
 329 {
 330         struct crypto_skcipher_spawn *spawn;
 331         struct skcipher_instance *inst;
 332         struct crypto_attr_type *algt;
 333         struct skcipher_alg *alg;
 334         const char *cipher_name;
 335         int err;
 336
 337         algt = crypto_get_attr_type(tb);
 338         if (IS_ERR(algt))
 339                 return PTR_ERR(algt);
 340
 341         if ((algt->type ^ CRYPTO_ALG_TYPE_SKCIPHER) & algt->mask)
 342                 return -EINVAL;
 343
 344         cipher_name = crypto_attr_alg_name(tb[1]);
 345         if (IS_ERR(cipher_name))
 346                 return PTR_ERR(cipher_name);
 347
 348         inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL);
 349         if (!inst)
 350                 return -ENOMEM;
 351
 352         spawn = skcipher_instance_ctx(inst);
 353
 354         crypto_set_skcipher_spawn(spawn, skcipher_crypto_instance(inst));
 355         err = crypto_grab_skcipher(spawn, cipher_name, 0,
 356                                    crypto_requires_sync(algt->type,
 357                                                         algt->mask));
 358         if (err)
 359                 goto err_free_inst;
 360
 361         alg = crypto_spawn_skcipher_alg(spawn);
 362
 363         err = -EINVAL;
 364         if (crypto_skcipher_alg_ivsize(alg) != alg->base.cra_blocksize)
 365                 goto err_drop_spawn;
 366
 367         if (strncmp(alg->base.cra_name, "cbc(", 4))
 368                 goto err_drop_spawn;
 369
 370         err = crypto_inst_setname(skcipher_crypto_instance(inst), "cts",
 371                                   &alg->base);
 372         if (err)
 373                 goto err_drop_spawn;
 374
 375         inst->alg.base.cra_flags = alg->base.cra_flags & CRYPTO_ALG_ASYNC;
 376         inst->alg.base.cra_priority = alg->base.cra_priority;
 377         inst->alg.base.cra_blocksize = alg->base.cra_blocksize;
 378         inst->alg.base.cra_alignmask = alg->base.cra_alignmask;
 379
 380         inst->alg.ivsize = alg->base.cra_blocksize;
 381         inst->alg.chunksize = crypto_skcipher_alg_chunksize(alg);
 382         inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(alg);
 383         inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(alg);
 384
 385         inst->alg.base.cra_ctxsize = sizeof(struct crypto_cts_ctx);
 386
 387         inst->alg.init = crypto_cts_init_tfm;
 388         inst->alg.exit = crypto_cts_exit_tfm;
 389
 390         inst->alg.setkey = crypto_cts_setkey;
 391         inst->alg.encrypt = crypto_cts_encrypt;
 392         inst->alg.decrypt = crypto_cts_decrypt;
 393
 394         inst->free = crypto_cts_free;
 395
 396         err = skcipher_register_instance(tmpl, inst);
 397         if (err)
 398                 goto err_drop_spawn;
 399
 400 out:
 401         return err;
 402
 403 err_drop_spawn:
 404         crypto_drop_skcipher(spawn);
 405 err_free_inst:
 406         kfree(inst);
 407         goto out;
 408 }
 409
 410 static struct crypto_template crypto_cts_tmpl = {
 411         .name = "cts",
 412         .create = crypto_cts_create,
 413         .module = THIS_MODULE,
 414 };
 415
 416 static int __init crypto_cts_module_init(void)
 417 {
 418         return crypto_register_template(&crypto_cts_tmpl);
 419 }
 420
 421 static void __exit crypto_cts_module_exit(void)
 422 {
 423         crypto_unregister_template(&crypto_cts_tmpl);
 424 }
 425
 426 subsys_initcall(crypto_cts_module_init);
 427 module_exit(crypto_cts_module_exit);
 428
 429 MODULE_LICENSE("Dual BSD/GPL");
 430 MODULE_DESCRIPTION("CTS-CBC CipherText Stealing for CBC");
 431 MODULE_ALIAS_CRYPTO("cts");