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 <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
  53 struct crypto_cts_ctx {
  54         struct crypto_blkcipher *child;
  55 };
  56
  57 static int crypto_cts_setkey(struct crypto_tfm *parent, const u8 *key,
  58                              unsigned int keylen)
  59 {
  60         struct crypto_cts_ctx *ctx = crypto_tfm_ctx(parent);
  61         struct crypto_blkcipher *child = ctx->child;
  62         int err;
  63
  64         crypto_blkcipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
  65         crypto_blkcipher_set_flags(child, crypto_tfm_get_flags(parent) &
  66                                        CRYPTO_TFM_REQ_MASK);
  67         err = crypto_blkcipher_setkey(child, key, keylen);
  68         crypto_tfm_set_flags(parent, crypto_blkcipher_get_flags(child) &
  69                                      CRYPTO_TFM_RES_MASK);
  70         return err;
  71 }
  72
  73 static int cts_cbc_encrypt(struct crypto_cts_ctx *ctx,
  74                            struct blkcipher_desc *desc,
  75                            struct scatterlist *dst,
  76                            struct scatterlist *src,
  77                            unsigned int offset,
  78                            unsigned int nbytes)
  79 {
  80         int bsize = crypto_blkcipher_blocksize(desc->tfm);
  81         u8 tmp[bsize], tmp2[bsize];
  82         struct blkcipher_desc lcldesc;
  83         struct scatterlist sgsrc[1], sgdst[1];
  84         int lastn = nbytes - bsize;
  85         u8 iv[bsize];
  86         u8 s[bsize * 2], d[bsize * 2];
  87         int err;
  88
  89         if (lastn < 0)
  90                 return -EINVAL;
  91
  92         sg_init_table(sgsrc, 1);
  93         sg_init_table(sgdst, 1);
  94
  95         memset(s, 0, sizeof(s));
  96         scatterwalk_map_and_copy(s, src, offset, nbytes, 0);
  97
  98         memcpy(iv, desc->info, bsize);
  99
 100         lcldesc.tfm = ctx->child;
 101         lcldesc.info = iv;
 102         lcldesc.flags = desc->flags;
 103
 104         sg_set_buf(&sgsrc[0], s, bsize);
 105         sg_set_buf(&sgdst[0], tmp, bsize);
 106         err = crypto_blkcipher_encrypt_iv(&lcldesc, sgdst, sgsrc, bsize);
 107
 108         memcpy(d + bsize, tmp, lastn);
 109
 110         lcldesc.info = tmp;
 111
 112         sg_set_buf(&sgsrc[0], s + bsize, bsize);
 113         sg_set_buf(&sgdst[0], tmp2, bsize);
 114         err = crypto_blkcipher_encrypt_iv(&lcldesc, sgdst, sgsrc, bsize);
 115
 116         memcpy(d, tmp2, bsize);
 117
 118         scatterwalk_map_and_copy(d, dst, offset, nbytes, 1);
 119
 120         memcpy(desc->info, tmp2, bsize);
 121
 122         return err;
 123 }
 124
 125 static int crypto_cts_encrypt(struct blkcipher_desc *desc,
 126                               struct scatterlist *dst, struct scatterlist *src,
 127                               unsigned int nbytes)
 128 {
 129         struct crypto_cts_ctx *ctx = crypto_blkcipher_ctx(desc->tfm);
 130         int bsize = crypto_blkcipher_blocksize(desc->tfm);
 131         int tot_blocks = (nbytes + bsize - 1) / bsize;
 132         int cbc_blocks = tot_blocks > 2 ? tot_blocks - 2 : 0;
 133         struct blkcipher_desc lcldesc;
 134         int err;
 135
 136         lcldesc.tfm = ctx->child;
 137         lcldesc.info = desc->info;
 138         lcldesc.flags = desc->flags;
 139
 140         if (tot_blocks == 1) {
 141                 err = crypto_blkcipher_encrypt_iv(&lcldesc, dst, src, bsize);
 142         } else if (nbytes <= bsize * 2) {
 143                 err = cts_cbc_encrypt(ctx, desc, dst, src, 0, nbytes);
 144         } else {
 145                 /* do normal function for tot_blocks - 2 */
 146                 err = crypto_blkcipher_encrypt_iv(&lcldesc, dst, src,
 147                                                         cbc_blocks * bsize);
 148                 if (err == 0) {
 149                         /* do cts for final two blocks */
 150                         err = cts_cbc_encrypt(ctx, desc, dst, src,
 151                                                 cbc_blocks * bsize,
 152                                                 nbytes - (cbc_blocks * bsize));
 153                 }
 154         }
 155
 156         return err;
 157 }
 158
 159 static int cts_cbc_decrypt(struct crypto_cts_ctx *ctx,
 160                            struct blkcipher_desc *desc,
 161                            struct scatterlist *dst,
 162                            struct scatterlist *src,
 163                            unsigned int offset,
 164                            unsigned int nbytes)
 165 {
 166         int bsize = crypto_blkcipher_blocksize(desc->tfm);
 167         u8 tmp[bsize];
 168         struct blkcipher_desc lcldesc;
 169         struct scatterlist sgsrc[1], sgdst[1];
 170         int lastn = nbytes - bsize;
 171         u8 iv[bsize];
 172         u8 s[bsize * 2], d[bsize * 2];
 173         int err;
 174
 175         if (lastn < 0)
 176                 return -EINVAL;
 177
 178         sg_init_table(sgsrc, 1);
 179         sg_init_table(sgdst, 1);
 180
 181         scatterwalk_map_and_copy(s, src, offset, nbytes, 0);
 182
 183         lcldesc.tfm = ctx->child;
 184         lcldesc.info = iv;
 185         lcldesc.flags = desc->flags;
 186
 187         /* 1. Decrypt Cn-1 (s) to create Dn (tmp)*/
 188         memset(iv, 0, sizeof(iv));
 189         sg_set_buf(&sgsrc[0], s, bsize);
 190         sg_set_buf(&sgdst[0], tmp, bsize);
 191         err = crypto_blkcipher_decrypt_iv(&lcldesc, sgdst, sgsrc, bsize);
 192         if (err)
 193                 return err;
 194         /* 2. Pad Cn with zeros at the end to create C of length BB */
 195         memset(iv, 0, sizeof(iv));
 196         memcpy(iv, s + bsize, lastn);
 197         /* 3. Exclusive-or Dn (tmp) with C (iv) to create Xn (tmp) */
 198         crypto_xor(tmp, iv, bsize);
 199         /* 4. Select the first Ln bytes of Xn (tmp) to create Pn */
 200         memcpy(d + bsize, tmp, lastn);
 201
 202         /* 5. Append the tail (BB - Ln) bytes of Xn (tmp) to Cn to create En */
 203         memcpy(s + bsize + lastn, tmp + lastn, bsize - lastn);
 204         /* 6. Decrypt En to create Pn-1 */
 205         memzero_explicit(iv, sizeof(iv));
 206
 207         sg_set_buf(&sgsrc[0], s + bsize, bsize);
 208         sg_set_buf(&sgdst[0], d, bsize);
 209         err = crypto_blkcipher_decrypt_iv(&lcldesc, sgdst, sgsrc, bsize);
 210
 211         /* XOR with previous block */
 212         crypto_xor(d, desc->info, bsize);
 213
 214         scatterwalk_map_and_copy(d, dst, offset, nbytes, 1);
 215
 216         memcpy(desc->info, s, bsize);
 217         return err;
 218 }
 219
 220 static int crypto_cts_decrypt(struct blkcipher_desc *desc,
 221                               struct scatterlist *dst, struct scatterlist *src,
 222                               unsigned int nbytes)
 223 {
 224         struct crypto_cts_ctx *ctx = crypto_blkcipher_ctx(desc->tfm);
 225         int bsize = crypto_blkcipher_blocksize(desc->tfm);
 226         int tot_blocks = (nbytes + bsize - 1) / bsize;
 227         int cbc_blocks = tot_blocks > 2 ? tot_blocks - 2 : 0;
 228         struct blkcipher_desc lcldesc;
 229         int err;
 230
 231         lcldesc.tfm = ctx->child;
 232         lcldesc.info = desc->info;
 233         lcldesc.flags = desc->flags;
 234
 235         if (tot_blocks == 1) {
 236                 err = crypto_blkcipher_decrypt_iv(&lcldesc, dst, src, bsize);
 237         } else if (nbytes <= bsize * 2) {
 238                 err = cts_cbc_decrypt(ctx, desc, dst, src, 0, nbytes);
 239         } else {
 240                 /* do normal function for tot_blocks - 2 */
 241                 err = crypto_blkcipher_decrypt_iv(&lcldesc, dst, src,
 242                                                         cbc_blocks * bsize);
 243                 if (err == 0) {
 244                         /* do cts for final two blocks */
 245                         err = cts_cbc_decrypt(ctx, desc, dst, src,
 246                                                 cbc_blocks * bsize,
 247                                                 nbytes - (cbc_blocks * bsize));
 248                 }
 249         }
 250         return err;
 251 }
 252
 253 static int crypto_cts_init_tfm(struct crypto_tfm *tfm)
 254 {
 255         struct crypto_instance *inst = (void *)tfm->__crt_alg;
 256         struct crypto_spawn *spawn = crypto_instance_ctx(inst);
 257         struct crypto_cts_ctx *ctx = crypto_tfm_ctx(tfm);
 258         struct crypto_blkcipher *cipher;
 259
 260         cipher = crypto_spawn_blkcipher(spawn);
 261         if (IS_ERR(cipher))
 262                 return PTR_ERR(cipher);
 263
 264         ctx->child = cipher;
 265         return 0;
 266 }
 267
 268 static void crypto_cts_exit_tfm(struct crypto_tfm *tfm)
 269 {
 270         struct crypto_cts_ctx *ctx = crypto_tfm_ctx(tfm);
 271         crypto_free_blkcipher(ctx->child);
 272 }
 273
 274 static struct crypto_instance *crypto_cts_alloc(struct rtattr **tb)
 275 {
 276         struct crypto_instance *inst;
 277         struct crypto_alg *alg;
 278         int err;
 279
 280         err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_BLKCIPHER);
 281         if (err)
 282                 return ERR_PTR(err);
 283
 284         alg = crypto_attr_alg(tb[1], CRYPTO_ALG_TYPE_BLKCIPHER,
 285                                   CRYPTO_ALG_TYPE_MASK);
 286         if (IS_ERR(alg))
 287                 return ERR_CAST(alg);
 288
 289         inst = ERR_PTR(-EINVAL);
 290         if (!is_power_of_2(alg->cra_blocksize))
 291                 goto out_put_alg;
 292
 293         if (strncmp(alg->cra_name, "cbc(", 4))
 294                 goto out_put_alg;
 295
 296         inst = crypto_alloc_instance("cts", alg);
 297         if (IS_ERR(inst))
 298                 goto out_put_alg;
 299
 300         inst->alg.cra_flags = CRYPTO_ALG_TYPE_BLKCIPHER;
 301         inst->alg.cra_priority = alg->cra_priority;
 302         inst->alg.cra_blocksize = alg->cra_blocksize;
 303         inst->alg.cra_alignmask = alg->cra_alignmask;
 304         inst->alg.cra_type = &crypto_blkcipher_type;
 305
 306         /* We access the data as u32s when xoring. */
 307         inst->alg.cra_alignmask |= __alignof__(u32) - 1;
 308
 309         inst->alg.cra_blkcipher.ivsize = alg->cra_blocksize;
 310         inst->alg.cra_blkcipher.min_keysize = alg->cra_blkcipher.min_keysize;
 311         inst->alg.cra_blkcipher.max_keysize = alg->cra_blkcipher.max_keysize;
 312
 313         inst->alg.cra_ctxsize = sizeof(struct crypto_cts_ctx);
 314
 315         inst->alg.cra_init = crypto_cts_init_tfm;
 316         inst->alg.cra_exit = crypto_cts_exit_tfm;
 317
 318         inst->alg.cra_blkcipher.setkey = crypto_cts_setkey;
 319         inst->alg.cra_blkcipher.encrypt = crypto_cts_encrypt;
 320         inst->alg.cra_blkcipher.decrypt = crypto_cts_decrypt;
 321
 322 out_put_alg:
 323         crypto_mod_put(alg);
 324         return inst;
 325 }
 326
 327 static void crypto_cts_free(struct crypto_instance *inst)
 328 {
 329         crypto_drop_spawn(crypto_instance_ctx(inst));
 330         kfree(inst);
 331 }
 332
 333 static struct crypto_template crypto_cts_tmpl = {
 334         .name = "cts",
 335         .alloc = crypto_cts_alloc,
 336         .free = crypto_cts_free,
 337         .module = THIS_MODULE,
 338 };
 339
 340 static int __init crypto_cts_module_init(void)
 341 {
 342         return crypto_register_template(&crypto_cts_tmpl);
 343 }
 344
 345 static void __exit crypto_cts_module_exit(void)
 346 {
 347         crypto_unregister_template(&crypto_cts_tmpl);
 348 }
 349
 350 module_init(crypto_cts_module_init);
 351 module_exit(crypto_cts_module_exit);
 352
 353 MODULE_LICENSE("Dual BSD/GPL");
 354 MODULE_DESCRIPTION("CTS-CBC CipherText Stealing for CBC");
 355 MODULE_ALIAS_CRYPTO("cts");