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 <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         memset(iv, 0, sizeof(iv));
  206         sg_set_buf(&sgsrc[0], s + bsize, bsize);
  207         sg_set_buf(&sgdst[0], d, bsize);
  208         err = crypto_blkcipher_decrypt_iv(&lcldesc, sgdst, sgsrc, bsize);
  209 
  210         /* XOR with previous block */
  211         crypto_xor(d, desc->info, bsize);
  212 
  213         scatterwalk_map_and_copy(d, dst, offset, nbytes, 1);
  214 
  215         memcpy(desc->info, s, bsize);
  216         return err;
  217 }
  218 
  219 static int crypto_cts_decrypt(struct blkcipher_desc *desc,
  220                               struct scatterlist *dst, struct scatterlist *src,
  221                               unsigned int nbytes)
  222 {
  223         struct crypto_cts_ctx *ctx = crypto_blkcipher_ctx(desc->tfm);
  224         int bsize = crypto_blkcipher_blocksize(desc->tfm);
  225         int tot_blocks = (nbytes + bsize - 1) / bsize;
  226         int cbc_blocks = tot_blocks > 2 ? tot_blocks - 2 : 0;
  227         struct blkcipher_desc lcldesc;
  228         int err;
  229 
  230         lcldesc.tfm = ctx->child;
  231         lcldesc.info = desc->info;
  232         lcldesc.flags = desc->flags;
  233 
  234         if (tot_blocks == 1) {
  235                 err = crypto_blkcipher_decrypt_iv(&lcldesc, dst, src, bsize);
  236         } else if (nbytes <= bsize * 2) {
  237                 err = cts_cbc_decrypt(ctx, desc, dst, src, 0, nbytes);
  238         } else {
  239                 /* do normal function for tot_blocks - 2 */
  240                 err = crypto_blkcipher_decrypt_iv(&lcldesc, dst, src,
  241                                                         cbc_blocks * bsize);
  242                 if (err == 0) {
  243                         /* do cts for final two blocks */
  244                         err = cts_cbc_decrypt(ctx, desc, dst, src,
  245                                                 cbc_blocks * bsize,
  246                                                 nbytes - (cbc_blocks * bsize));
  247                 }
  248         }
  249         return err;
  250 }
  251 
  252 static int crypto_cts_init_tfm(struct crypto_tfm *tfm)
  253 {
  254         struct crypto_instance *inst = (void *)tfm->__crt_alg;
  255         struct crypto_spawn *spawn = crypto_instance_ctx(inst);
  256         struct crypto_cts_ctx *ctx = crypto_tfm_ctx(tfm);
  257         struct crypto_blkcipher *cipher;
  258 
  259         cipher = crypto_spawn_blkcipher(spawn);
  260         if (IS_ERR(cipher))
  261                 return PTR_ERR(cipher);
  262 
  263         ctx->child = cipher;
  264         return 0;
  265 }
  266 
  267 static void crypto_cts_exit_tfm(struct crypto_tfm *tfm)
  268 {
  269         struct crypto_cts_ctx *ctx = crypto_tfm_ctx(tfm);
  270         crypto_free_blkcipher(ctx->child);
  271 }
  272 
  273 static struct crypto_instance *crypto_cts_alloc(struct rtattr **tb)
  274 {
  275         struct crypto_instance *inst;
  276         struct crypto_alg *alg;
  277         int err;
  278 
  279         err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_BLKCIPHER);
  280         if (err)
  281                 return ERR_PTR(err);
  282 
  283         alg = crypto_attr_alg(tb[1], CRYPTO_ALG_TYPE_BLKCIPHER,
  284                                   CRYPTO_ALG_TYPE_MASK);
  285         err = PTR_ERR(alg);
  286         if (IS_ERR(alg))
  287                 return ERR_PTR(err);
  288 
  289         inst = ERR_PTR(-EINVAL);
  290         if (!is_power_of_2(alg->cra_blocksize))
  291                 goto out_put_alg;
  292 
  293         inst = crypto_alloc_instance("cts", alg);
  294         if (IS_ERR(inst))
  295                 goto out_put_alg;
  296 
  297         inst->alg.cra_flags = CRYPTO_ALG_TYPE_BLKCIPHER;
  298         inst->alg.cra_priority = alg->cra_priority;
  299         inst->alg.cra_blocksize = alg->cra_blocksize;
  300         inst->alg.cra_alignmask = alg->cra_alignmask;
  301         inst->alg.cra_type = &crypto_blkcipher_type;
  302 
  303         /* We access the data as u32s when xoring. */
  304         inst->alg.cra_alignmask |= __alignof__(u32) - 1;
  305 
  306         inst->alg.cra_blkcipher.ivsize = alg->cra_blocksize;
  307         inst->alg.cra_blkcipher.min_keysize = alg->cra_blkcipher.min_keysize;
  308         inst->alg.cra_blkcipher.max_keysize = alg->cra_blkcipher.max_keysize;
  309 
  310         inst->alg.cra_blkcipher.geniv = "seqiv";
  311 
  312         inst->alg.cra_ctxsize = sizeof(struct crypto_cts_ctx);
  313 
  314         inst->alg.cra_init = crypto_cts_init_tfm;
  315         inst->alg.cra_exit = crypto_cts_exit_tfm;
  316 
  317         inst->alg.cra_blkcipher.setkey = crypto_cts_setkey;
  318         inst->alg.cra_blkcipher.encrypt = crypto_cts_encrypt;
  319         inst->alg.cra_blkcipher.decrypt = crypto_cts_decrypt;
  320 
  321 out_put_alg:
  322         crypto_mod_put(alg);
  323         return inst;
  324 }
  325 
  326 static void crypto_cts_free(struct crypto_instance *inst)
  327 {
  328         crypto_drop_spawn(crypto_instance_ctx(inst));
  329         kfree(inst);
  330 }
  331 
  332 static struct crypto_template crypto_cts_tmpl = {
  333         .name = "cts",
  334         .alloc = crypto_cts_alloc,
  335         .free = crypto_cts_free,
  336         .module = THIS_MODULE,
  337 };
  338 
  339 static int __init crypto_cts_module_init(void)
  340 {
  341         return crypto_register_template(&crypto_cts_tmpl);
  342 }
  343 
  344 static void __exit crypto_cts_module_exit(void)
  345 {
  346         crypto_unregister_template(&crypto_cts_tmpl);
  347 }
  348 
  349 module_init(crypto_cts_module_init);
  350 module_exit(crypto_cts_module_exit);
  351 
  352 MODULE_LICENSE("Dual BSD/GPL");
  353 MODULE_DESCRIPTION("CTS-CBC CipherText Stealing for CBC");
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FreeBSD/Linux Kernel Cross Reference sys/crypto/cts.c

FreeBSD/Linux Kernel Cross Reference
sys/crypto/cts.c
