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 || 140 (err == -EBUSY && req->base.flags & CRYPTO_TFM_REQ_MAY_BACKLOG)) 141 return; 142 143 out: 144 skcipher_request_complete(req, err); 145 } 146 147 static int crypto_cts_encrypt(struct skcipher_request *req) 148 { 149 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); 150 struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req); 151 struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm); 152 struct skcipher_request *subreq = &rctx->subreq; 153 int bsize = crypto_skcipher_blocksize(tfm); 154 unsigned int nbytes = req->cryptlen; 155 int cbc_blocks = (nbytes + bsize - 1) / bsize - 1; 156 unsigned int offset; 157 158 skcipher_request_set_tfm(subreq, ctx->child); 159 160 if (cbc_blocks <= 0) { 161 skcipher_request_set_callback(subreq, req->base.flags, 162 req->base.complete, 163 req->base.data); 164 skcipher_request_set_crypt(subreq, req->src, req->dst, nbytes, 165 req->iv); 166 return crypto_skcipher_encrypt(subreq); 167 } 168 169 offset = cbc_blocks * bsize; 170 rctx->offset = offset; 171 172 skcipher_request_set_callback(subreq, req->base.flags, 173 crypto_cts_encrypt_done, req); 174 skcipher_request_set_crypt(subreq, req->src, req->dst, 175 offset, req->iv); 176 177 return crypto_skcipher_encrypt(subreq) ?: 178 cts_cbc_encrypt(req); 179 } 180 181 static int cts_cbc_decrypt(struct skcipher_request *req) 182 { 183 struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req); 184 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); 185 struct skcipher_request *subreq = &rctx->subreq; 186 int bsize = crypto_skcipher_blocksize(tfm); 187 u8 d[bsize * 2] __aligned(__alignof__(u32)); 188 struct scatterlist *sg; 189 unsigned int offset; 190 u8 *space; 191 int lastn; 192 193 offset = rctx->offset; 194 lastn = req->cryptlen - offset; 195 196 sg = scatterwalk_ffwd(rctx->sg, req->dst, offset - bsize); 197 198 /* 1. Decrypt Cn-1 (s) to create Dn */ 199 scatterwalk_map_and_copy(d + bsize, sg, 0, bsize, 0); 200 space = crypto_cts_reqctx_space(req); 201 crypto_xor(d + bsize, space, bsize); 202 /* 2. Pad Cn with zeros at the end to create C of length BB */ 203 memset(d, 0, bsize); 204 scatterwalk_map_and_copy(d, req->src, offset, lastn, 0); 205 /* 3. Exclusive-or Dn with C to create Xn */ 206 /* 4. Select the first Ln bytes of Xn to create Pn */ 207 crypto_xor(d + bsize, d, lastn); 208 209 /* 5. Append the tail (BB - Ln) bytes of Xn to Cn to create En */ 210 memcpy(d + lastn, d + bsize + lastn, bsize - lastn); 211 /* 6. Decrypt En to create Pn-1 */ 212 213 scatterwalk_map_and_copy(d, sg, 0, bsize + lastn, 1); 214 memzero_explicit(d, sizeof(d)); 215 216 skcipher_request_set_callback(subreq, req->base.flags & 217 CRYPTO_TFM_REQ_MAY_BACKLOG, 218 cts_cbc_crypt_done, req); 219 220 skcipher_request_set_crypt(subreq, sg, sg, bsize, space); 221 return crypto_skcipher_decrypt(subreq); 222 } 223 224 static void crypto_cts_decrypt_done(struct crypto_async_request *areq, int err) 225 { 226 struct skcipher_request *req = areq->data; 227 228 if (err) 229 goto out; 230 231 err = cts_cbc_decrypt(req); 232 if (err == -EINPROGRESS || 233 (err == -EBUSY && req->base.flags & CRYPTO_TFM_REQ_MAY_BACKLOG)) 234 return; 235 236 out: 237 skcipher_request_complete(req, err); 238 } 239 240 static int crypto_cts_decrypt(struct skcipher_request *req) 241 { 242 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); 243 struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req); 244 struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm); 245 struct skcipher_request *subreq = &rctx->subreq; 246 int bsize = crypto_skcipher_blocksize(tfm); 247 unsigned int nbytes = req->cryptlen; 248 int cbc_blocks = (nbytes + bsize - 1) / bsize - 1; 249 unsigned int offset; 250 u8 *space; 251 252 skcipher_request_set_tfm(subreq, ctx->child); 253 254 if (cbc_blocks <= 0) { 255 skcipher_request_set_callback(subreq, req->base.flags, 256 req->base.complete, 257 req->base.data); 258 skcipher_request_set_crypt(subreq, req->src, req->dst, nbytes, 259 req->iv); 260 return crypto_skcipher_decrypt(subreq); 261 } 262 263 skcipher_request_set_callback(subreq, req->base.flags, 264 crypto_cts_decrypt_done, req); 265 266 space = crypto_cts_reqctx_space(req); 267 268 offset = cbc_blocks * bsize; 269 rctx->offset = offset; 270 271 if (cbc_blocks <= 1) 272 memcpy(space, req->iv, bsize); 273 else 274 scatterwalk_map_and_copy(space, req->src, offset - 2 * bsize, 275 bsize, 0); 276 277 skcipher_request_set_crypt(subreq, req->src, req->dst, 278 offset, req->iv); 279 280 return crypto_skcipher_decrypt(subreq) ?: 281 cts_cbc_decrypt(req); 282 } 283 284 static int crypto_cts_init_tfm(struct crypto_skcipher *tfm) 285 { 286 struct skcipher_instance *inst = skcipher_alg_instance(tfm); 287 struct crypto_skcipher_spawn *spawn = skcipher_instance_ctx(inst); 288 struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm); 289 struct crypto_skcipher *cipher; 290 unsigned reqsize; 291 unsigned bsize; 292 unsigned align; 293 294 cipher = crypto_spawn_skcipher(spawn); 295 if (IS_ERR(cipher)) 296 return PTR_ERR(cipher); 297 298 ctx->child = cipher; 299 300 align = crypto_skcipher_alignmask(tfm); 301 bsize = crypto_skcipher_blocksize(cipher); 302 reqsize = ALIGN(sizeof(struct crypto_cts_reqctx) + 303 crypto_skcipher_reqsize(cipher), 304 crypto_tfm_ctx_alignment()) + 305 (align & ~(crypto_tfm_ctx_alignment() - 1)) + bsize; 306 307 crypto_skcipher_set_reqsize(tfm, reqsize); 308 309 return 0; 310 } 311 312 static void crypto_cts_exit_tfm(struct crypto_skcipher *tfm) 313 { 314 struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm); 315 316 crypto_free_skcipher(ctx->child); 317 } 318 319 static void crypto_cts_free(struct skcipher_instance *inst) 320 { 321 crypto_drop_skcipher(skcipher_instance_ctx(inst)); 322 kfree(inst); 323 } 324 325 static int crypto_cts_create(struct crypto_template *tmpl, struct rtattr **tb) 326 { 327 struct crypto_skcipher_spawn *spawn; 328 struct skcipher_instance *inst; 329 struct crypto_attr_type *algt; 330 struct skcipher_alg *alg; 331 const char *cipher_name; 332 int err; 333 334 algt = crypto_get_attr_type(tb); 335 if (IS_ERR(algt)) 336 return PTR_ERR(algt); 337 338 if ((algt->type ^ CRYPTO_ALG_TYPE_SKCIPHER) & algt->mask) 339 return -EINVAL; 340 341 cipher_name = crypto_attr_alg_name(tb[1]); 342 if (IS_ERR(cipher_name)) 343 return PTR_ERR(cipher_name); 344 345 inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL); 346 if (!inst) 347 return -ENOMEM; 348 349 spawn = skcipher_instance_ctx(inst); 350 351 crypto_set_skcipher_spawn(spawn, skcipher_crypto_instance(inst)); 352 err = crypto_grab_skcipher(spawn, cipher_name, 0, 353 crypto_requires_sync(algt->type, 354 algt->mask)); 355 if (err) 356 goto err_free_inst; 357 358 alg = crypto_spawn_skcipher_alg(spawn); 359 360 err = -EINVAL; 361 if (crypto_skcipher_alg_ivsize(alg) != alg->base.cra_blocksize) 362 goto err_drop_spawn; 363 364 if (strncmp(alg->base.cra_name, "cbc(", 4)) 365 goto err_drop_spawn; 366 367 err = crypto_inst_setname(skcipher_crypto_instance(inst), "cts", 368 &alg->base); 369 if (err) 370 goto err_drop_spawn; 371 372 inst->alg.base.cra_flags = alg->base.cra_flags & CRYPTO_ALG_ASYNC; 373 inst->alg.base.cra_priority = alg->base.cra_priority; 374 inst->alg.base.cra_blocksize = alg->base.cra_blocksize; 375 inst->alg.base.cra_alignmask = alg->base.cra_alignmask; 376 377 inst->alg.ivsize = alg->base.cra_blocksize; 378 inst->alg.chunksize = crypto_skcipher_alg_chunksize(alg); 379 inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(alg); 380 inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(alg); 381 382 inst->alg.base.cra_ctxsize = sizeof(struct crypto_cts_ctx); 383 384 inst->alg.init = crypto_cts_init_tfm; 385 inst->alg.exit = crypto_cts_exit_tfm; 386 387 inst->alg.setkey = crypto_cts_setkey; 388 inst->alg.encrypt = crypto_cts_encrypt; 389 inst->alg.decrypt = crypto_cts_decrypt; 390 391 inst->free = crypto_cts_free; 392 393 err = skcipher_register_instance(tmpl, inst); 394 if (err) 395 goto err_drop_spawn; 396 397 out: 398 return err; 399 400 err_drop_spawn: 401 crypto_drop_skcipher(spawn); 402 err_free_inst: 403 kfree(inst); 404 goto out; 405 } 406 407 static struct crypto_template crypto_cts_tmpl = { 408 .name = "cts", 409 .create = crypto_cts_create, 410 .module = THIS_MODULE, 411 }; 412 413 static int __init crypto_cts_module_init(void) 414 { 415 return crypto_register_template(&crypto_cts_tmpl); 416 } 417 418 static void __exit crypto_cts_module_exit(void) 419 { 420 crypto_unregister_template(&crypto_cts_tmpl); 421 } 422 423 module_init(crypto_cts_module_init); 424 module_exit(crypto_cts_module_exit); 425 426 MODULE_LICENSE("Dual BSD/GPL"); 427 MODULE_DESCRIPTION("CTS-CBC CipherText Stealing for CBC"); 428 MODULE_ALIAS_CRYPTO("cts"); 429