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         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[MAX_CIPHER_BLOCKSIZE * 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 || err == -EBUSY)
 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         inst->alg.ivsize = alg->base.cra_blocksize;
 377         inst->alg.chunksize = crypto_skcipher_alg_chunksize(alg);
 378         inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(alg);
 379         inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(alg);
 380
 381         inst->alg.base.cra_ctxsize = sizeof(struct crypto_cts_ctx);
 382
 383         inst->alg.init = crypto_cts_init_tfm;
 384         inst->alg.exit = crypto_cts_exit_tfm;
 385
 386         inst->alg.setkey = crypto_cts_setkey;
 387         inst->alg.encrypt = crypto_cts_encrypt;
 388         inst->alg.decrypt = crypto_cts_decrypt;
 389
 390         inst->free = crypto_cts_free;
 391
 392         err = skcipher_register_instance(tmpl, inst);
 393         if (err)
 394                 goto err_drop_spawn;
 395
 396 out:
 397         return err;
 398
 399 err_drop_spawn:
 400         crypto_drop_skcipher(spawn);
 401 err_free_inst:
 402         kfree(inst);
 403         goto out;
 404 }
 405
 406 static struct crypto_template crypto_cts_tmpl = {
 407         .name = "cts",
 408         .create = crypto_cts_create,
 409         .module = THIS_MODULE,
 410 };
 411
 412 static int __init crypto_cts_module_init(void)
 413 {
 414         return crypto_register_template(&crypto_cts_tmpl);
 415 }
 416
 417 static void __exit crypto_cts_module_exit(void)
 418 {
 419         crypto_unregister_template(&crypto_cts_tmpl);
 420 }
 421
 422 module_init(crypto_cts_module_init);
 423 module_exit(crypto_cts_module_exit);
 424
 425 MODULE_LICENSE("Dual BSD/GPL");
 426 MODULE_DESCRIPTION("CTS-CBC CipherText Stealing for CBC");
 427 MODULE_ALIAS_CRYPTO("cts");