linux/crypto/cts.c
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   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
  55struct crypto_cts_ctx {
  56        struct crypto_skcipher *child;
  57};
  58
  59struct crypto_cts_reqctx {
  60        struct scatterlist sg[2];
  61        unsigned offset;
  62        struct skcipher_request subreq;
  63};
  64
  65static 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
  76static 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
  88static 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
  98static 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
 128static 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
 139out:
 140        skcipher_request_complete(req, err);
 141}
 142
 143static 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
 179static 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
 222static 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
 233out:
 234        skcipher_request_complete(req, err);
 235}
 236
 237static 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
 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_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
 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 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) {
 383err_free_inst:
 384                crypto_cts_free(inst);
 385        }
 386        return err;
 387}
 388
 389static struct crypto_template crypto_cts_tmpl = {
 390        .name = "cts",
 391        .create = crypto_cts_create,
 392        .module = THIS_MODULE,
 393};
 394
 395static int __init crypto_cts_module_init(void)
 396{
 397        return crypto_register_template(&crypto_cts_tmpl);
 398}
 399
 400static void __exit crypto_cts_module_exit(void)
 401{
 402        crypto_unregister_template(&crypto_cts_tmpl);
 403}
 404
 405subsys_initcall(crypto_cts_module_init);
 406module_exit(crypto_cts_module_exit);
 407
 408MODULE_LICENSE("Dual BSD/GPL");
 409MODULE_DESCRIPTION("CTS-CBC CipherText Stealing for CBC");
 410MODULE_ALIAS_CRYPTO("cts");
 411
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