LXR linux/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
  53struct crypto_cts_ctx {
  54        struct crypto_skcipher *child;
  55};
  56
  57struct crypto_cts_reqctx {
  58        struct scatterlist sg[2];
  59        unsigned offset;
  60        struct skcipher_request subreq;
  61};
  62
  63static inline u8 *crypto_cts_reqctx_space(struct skcipher_request *req)
  64{
  65        struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
  66        struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
  67        struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm);
  68        struct crypto_skcipher *child = ctx->child;
  69
  70        return PTR_ALIGN((u8 *)(rctx + 1) + crypto_skcipher_reqsize(child),
  71                         crypto_skcipher_alignmask(tfm) + 1);
  72}
  73
  74static int crypto_cts_setkey(struct crypto_skcipher *parent, const u8 *key,
  75                             unsigned int keylen)
  76{
  77        struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(parent);
  78        struct crypto_skcipher *child = ctx->child;
  79        int err;
  80
  81        crypto_skcipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
  82        crypto_skcipher_set_flags(child, crypto_skcipher_get_flags(parent) &
  83                                         CRYPTO_TFM_REQ_MASK);
  84        err = crypto_skcipher_setkey(child, key, keylen);
  85        crypto_skcipher_set_flags(parent, crypto_skcipher_get_flags(child) &
  86                                          CRYPTO_TFM_RES_MASK);
  87        return err;
  88}
  89
  90static void cts_cbc_crypt_done(struct crypto_async_request *areq, int err)
  91{
  92        struct skcipher_request *req = areq->data;
  93
  94        if (err == -EINPROGRESS)
  95                return;
  96
  97        skcipher_request_complete(req, err);
  98}
  99
 100static int cts_cbc_encrypt(struct skcipher_request *req)
 101{
 102        struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req);
 103        struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 104        struct skcipher_request *subreq = &rctx->subreq;
 105        int bsize = crypto_skcipher_blocksize(tfm);
 106        u8 d[bsize * 2] __attribute__ ((aligned(__alignof__(u32))));
 107        struct scatterlist *sg;
 108        unsigned int offset;
 109        int lastn;
 110
 111        offset = rctx->offset;
 112        lastn = req->cryptlen - offset;
 113
 114        sg = scatterwalk_ffwd(rctx->sg, req->dst, offset - bsize);
 115        scatterwalk_map_and_copy(d + bsize, sg, 0, bsize, 0);
 116
 117        memset(d, 0, bsize);
 118        scatterwalk_map_and_copy(d, req->src, offset, lastn, 0);
 119
 120        scatterwalk_map_and_copy(d, sg, 0, bsize + lastn, 1);
 121        memzero_explicit(d, sizeof(d));
 122
 123        skcipher_request_set_callback(subreq, req->base.flags &
 124                                              CRYPTO_TFM_REQ_MAY_BACKLOG,
 125                                      cts_cbc_crypt_done, req);
 126        skcipher_request_set_crypt(subreq, sg, sg, bsize, req->iv);
 127        return crypto_skcipher_encrypt(subreq);
 128}
 129
 130static void crypto_cts_encrypt_done(struct crypto_async_request *areq, int err)
 131{
 132        struct skcipher_request *req = areq->data;
 133
 134        if (err)
 135                goto out;
 136
 137        err = cts_cbc_encrypt(req);
 138        if (err == -EINPROGRESS ||
 139            (err == -EBUSY && req->base.flags & CRYPTO_TFM_REQ_MAY_BACKLOG))
 140                return;
 141
 142out:
 143        skcipher_request_complete(req, err);
 144}
 145
 146static 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
 180static 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] __attribute__ ((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
 223static 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 ||
 232            (err == -EBUSY && req->base.flags & CRYPTO_TFM_REQ_MAY_BACKLOG))
 233                return;
 234
 235out:
 236        skcipher_request_complete(req, err);
 237}
 238
 239static 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
 283static 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_skcipher2(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
 311static 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
 318static void crypto_cts_free(struct skcipher_instance *inst)
 319{
 320        crypto_drop_skcipher(skcipher_instance_ctx(inst));
 321        kfree(inst);
 322}
 323
 324static 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_skcipher2(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        /* We access the data as u32s when xoring. */
 377        inst->alg.base.cra_alignmask |= __alignof__(u32) - 1;
 378
 379        inst->alg.ivsize = alg->base.cra_blocksize;
 380        inst->alg.chunksize = crypto_skcipher_alg_chunksize(alg);
 381        inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(alg);
 382        inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(alg);
 383
 384        inst->alg.base.cra_ctxsize = sizeof(struct crypto_cts_ctx);
 385
 386        inst->alg.init = crypto_cts_init_tfm;
 387        inst->alg.exit = crypto_cts_exit_tfm;
 388
 389        inst->alg.setkey = crypto_cts_setkey;
 390        inst->alg.encrypt = crypto_cts_encrypt;
 391        inst->alg.decrypt = crypto_cts_decrypt;
 392
 393        inst->free = crypto_cts_free;
 394
 395        err = skcipher_register_instance(tmpl, inst);
 396        if (err)
 397                goto err_drop_spawn;
 398
 399out:
 400        return err;
 401
 402err_drop_spawn:
 403        crypto_drop_skcipher(spawn);
 404err_free_inst:
 405        kfree(inst);
 406        goto out;
 407}
 408
 409static struct crypto_template crypto_cts_tmpl = {
 410        .name = "cts",
 411        .create = crypto_cts_create,
 412        .module = THIS_MODULE,
 413};
 414
 415static int __init crypto_cts_module_init(void)
 416{
 417        return crypto_register_template(&crypto_cts_tmpl);
 418}
 419
 420static void __exit crypto_cts_module_exit(void)
 421{
 422        crypto_unregister_template(&crypto_cts_tmpl);
 423}
 424
 425module_init(crypto_cts_module_init);
 426module_exit(crypto_cts_module_exit);
 427
 428MODULE_LICENSE("Dual BSD/GPL");
 429MODULE_DESCRIPTION("CTS-CBC CipherText Stealing for CBC");
 430MODULE_ALIAS_CRYPTO("cts");
 431