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 #include <linux/compiler.h> 53 54 struct crypto_cts_ctx { 55 struct crypto_skcipher *child; 56 }; 57 58 struct crypto_cts_reqctx { 59 struct scatterlist sg[2]; 60 unsigned offset; 61 struct skcipher_request subreq; 62 }; 63 64 static inline u8 *crypto_cts_reqctx_space(struct skcipher_request *req) 65 { 66 struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req); 67 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); 68 struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm); 69 struct crypto_skcipher *child = ctx->child; 70 71 return PTR_ALIGN((u8 *)(rctx + 1) + crypto_skcipher_reqsize(child), 72 crypto_skcipher_alignmask(tfm) + 1); 73 } 74 75 static int crypto_cts_setkey(struct crypto_skcipher *parent, const u8 *key, 76 unsigned int keylen) 77 { 78 struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(parent); 79 struct crypto_skcipher *child = ctx->child; 80 int err; 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 err = crypto_skcipher_setkey(child, key, keylen); 86 crypto_skcipher_set_flags(parent, crypto_skcipher_get_flags(child) & 87 CRYPTO_TFM_RES_MASK); 88 return err; 89 } 90 91 static void cts_cbc_crypt_done(struct crypto_async_request *areq, int err) 92 { 93 struct skcipher_request *req = areq->data; 94 95 if (err == -EINPROGRESS) 96 return; 97 98 skcipher_request_complete(req, err); 99 } 100 101 static int cts_cbc_encrypt(struct skcipher_request *req) 102 { 103 struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req); 104 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); 105 struct skcipher_request *subreq = &rctx->subreq; 106 int bsize = crypto_skcipher_blocksize(tfm); 107 u8 d[bsize * 2] __aligned(__alignof__(u32)); 108 struct scatterlist *sg; 109 unsigned int offset; 110 int lastn; 111 112 offset = rctx->offset; 113 lastn = req->cryptlen - offset; 114 115 sg = scatterwalk_ffwd(rctx->sg, req->dst, offset - bsize); 116 scatterwalk_map_and_copy(d + bsize, sg, 0, bsize, 0); 117 118 memset(d, 0, bsize); 119 scatterwalk_map_and_copy(d, req->src, offset, lastn, 0); 120 121 scatterwalk_map_and_copy(d, sg, 0, bsize + lastn, 1); 122 memzero_explicit(d, sizeof(d)); 123 124 skcipher_request_set_callback(subreq, req->base.flags & 125 CRYPTO_TFM_REQ_MAY_BACKLOG, 126 cts_cbc_crypt_done, req); 127 skcipher_request_set_crypt(subreq, sg, sg, bsize, req->iv); 128 return crypto_skcipher_encrypt(subreq); 129 } 130 131 static void crypto_cts_encrypt_done(struct crypto_async_request *areq, int err) 132 { 133 struct skcipher_request *req = areq->data; 134 135 if (err) 136 goto out; 137 138 err = cts_cbc_encrypt(req); 139 if (err == -EINPROGRESS || err == -EBUSY) 140 return; 141 142 out: 143 skcipher_request_complete(req, err); 144 } 145 146 static 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 } 179 180 static 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] __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 } 222 223 static 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 || err == -EBUSY) 232 return; 233 234 out: 235 skcipher_request_complete(req, err); 236 } 237 238 static int crypto_cts_decrypt(struct skcipher_request *req) 239 { 240 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); 241 struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req); 242 struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm); 243 struct skcipher_request *subreq = &rctx->subreq; 244 int bsize = crypto_skcipher_blocksize(tfm); 245 unsigned int nbytes = req->cryptlen; 246 int cbc_blocks = (nbytes + bsize - 1) / bsize - 1; 247 unsigned int offset; 248 u8 *space; 249 250 skcipher_request_set_tfm(subreq, ctx->child); 251 252 if (cbc_blocks <= 0) { 253 skcipher_request_set_callback(subreq, req->base.flags, 254 req->base.complete, 255 req->base.data); 256 skcipher_request_set_crypt(subreq, req->src, req->dst, nbytes, 257 req->iv); 258 return crypto_skcipher_decrypt(subreq); 259 } 260 261 skcipher_request_set_callback(subreq, req->base.flags, 262 crypto_cts_decrypt_done, req); 263 264 space = crypto_cts_reqctx_space(req); 265 266 offset = cbc_blocks * bsize; 267 rctx->offset = offset; 268 269 if (cbc_blocks <= 1) 270 memcpy(space, req->iv, bsize); 271 else 272 scatterwalk_map_and_copy(space, req->src, offset - 2 * bsize, 273 bsize, 0); 274 275 skcipher_request_set_crypt(subreq, req->src, req->dst, 276 offset, req->iv); 277 278 return crypto_skcipher_decrypt(subreq) ?: 279 cts_cbc_decrypt(req); 280 } 281 282 static int crypto_cts_init_tfm(struct crypto_skcipher *tfm) 283 { 284 struct skcipher_instance *inst = skcipher_alg_instance(tfm); 285 struct crypto_skcipher_spawn *spawn = skcipher_instance_ctx(inst); 286 struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm); 287 struct crypto_skcipher *cipher; 288 unsigned reqsize; 289 unsigned bsize; 290 unsigned align; 291 292 cipher = crypto_spawn_skcipher(spawn); 293 if (IS_ERR(cipher)) 294 return PTR_ERR(cipher); 295 296 ctx->child = cipher; 297 298 align = crypto_skcipher_alignmask(tfm); 299 bsize = crypto_skcipher_blocksize(cipher); 300 reqsize = ALIGN(sizeof(struct crypto_cts_reqctx) + 301 crypto_skcipher_reqsize(cipher), 302 crypto_tfm_ctx_alignment()) + 303 (align & ~(crypto_tfm_ctx_alignment() - 1)) + bsize; 304 305 crypto_skcipher_set_reqsize(tfm, reqsize); 306 307 return 0; 308 } 309 310 static void crypto_cts_exit_tfm(struct crypto_skcipher *tfm) 311 { 312 struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm); 313 314 crypto_free_skcipher(ctx->child); 315 } 316 317 static void crypto_cts_free(struct skcipher_instance *inst) 318 { 319 crypto_drop_skcipher(skcipher_instance_ctx(inst)); 320 kfree(inst); 321 } 322 323 static int crypto_cts_create(struct crypto_template *tmpl, struct rtattr **tb) 324 { 325 struct crypto_skcipher_spawn *spawn; 326 struct skcipher_instance *inst; 327 struct crypto_attr_type *algt; 328 struct skcipher_alg *alg; 329 const char *cipher_name; 330 int err; 331 332 algt = crypto_get_attr_type(tb); 333 if (IS_ERR(algt)) 334 return PTR_ERR(algt); 335 336 if ((algt->type ^ CRYPTO_ALG_TYPE_SKCIPHER) & algt->mask) 337 return -EINVAL; 338 339 cipher_name = crypto_attr_alg_name(tb[1]); 340 if (IS_ERR(cipher_name)) 341 return PTR_ERR(cipher_name); 342 343 inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL); 344 if (!inst) 345 return -ENOMEM; 346 347 spawn = skcipher_instance_ctx(inst); 348 349 crypto_set_skcipher_spawn(spawn, skcipher_crypto_instance(inst)); 350 err = crypto_grab_skcipher(spawn, cipher_name, 0, 351 crypto_requires_sync(algt->type, 352 algt->mask)); 353 if (err) 354 goto err_free_inst; 355 356 alg = crypto_spawn_skcipher_alg(spawn); 357 358 err = -EINVAL; 359 if (crypto_skcipher_alg_ivsize(alg) != alg->base.cra_blocksize) 360 goto err_drop_spawn; 361 362 if (strncmp(alg->base.cra_name, "cbc(", 4)) 363 goto err_drop_spawn; 364 365 err = crypto_inst_setname(skcipher_crypto_instance(inst), "cts", 366 &alg->base); 367 if (err) 368 goto err_drop_spawn; 369 370 inst->alg.base.cra_flags = alg->base.cra_flags & CRYPTO_ALG_ASYNC; 371 inst->alg.base.cra_priority = alg->base.cra_priority; 372 inst->alg.base.cra_blocksize = alg->base.cra_blocksize; 373 inst->alg.base.cra_alignmask = alg->base.cra_alignmask; 374 375 inst->alg.ivsize = alg->base.cra_blocksize; 376 inst->alg.chunksize = crypto_skcipher_alg_chunksize(alg); 377 inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(alg); 378 inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(alg); 379 380 inst->alg.base.cra_ctxsize = sizeof(struct crypto_cts_ctx); 381 382 inst->alg.init = crypto_cts_init_tfm; 383 inst->alg.exit = crypto_cts_exit_tfm; 384 385 inst->alg.setkey = crypto_cts_setkey; 386 inst->alg.encrypt = crypto_cts_encrypt; 387 inst->alg.decrypt = crypto_cts_decrypt; 388 389 inst->free = crypto_cts_free; 390 391 err = skcipher_register_instance(tmpl, inst); 392 if (err) 393 goto err_drop_spawn; 394 395 out: 396 return err; 397 398 err_drop_spawn: 399 crypto_drop_skcipher(spawn); 400 err_free_inst: 401 kfree(inst); 402 goto out; 403 } 404 405 static struct crypto_template crypto_cts_tmpl = { 406 .name = "cts", 407 .create = crypto_cts_create, 408 .module = THIS_MODULE, 409 }; 410 411 static int __init crypto_cts_module_init(void) 412 { 413 return crypto_register_template(&crypto_cts_tmpl); 414 } 415 416 static void __exit crypto_cts_module_exit(void) 417 { 418 crypto_unregister_template(&crypto_cts_tmpl); 419 } 420 421 module_init(crypto_cts_module_init); 422 module_exit(crypto_cts_module_exit); 423 424 MODULE_LICENSE("Dual BSD/GPL"); 425 MODULE_DESCRIPTION("CTS-CBC CipherText Stealing for CBC"); 426 MODULE_ALIAS_CRYPTO("cts"); 427