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 55 struct crypto_cts_ctx { 56 struct crypto_skcipher *child; 57 }; 58 59 struct crypto_cts_reqctx { 60 struct scatterlist sg[2]; 61 unsigned offset; 62 struct skcipher_request subreq; 63 }; 64 65 static 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 76 static 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 int err; 82 83 crypto_skcipher_clear_flags(child, CRYPTO_TFM_REQ_MASK); 84 crypto_skcipher_set_flags(child, crypto_skcipher_get_flags(parent) & 85 CRYPTO_TFM_REQ_MASK); 86 err = crypto_skcipher_setkey(child, key, keylen); 87 crypto_skcipher_set_flags(parent, crypto_skcipher_get_flags(child) & 88 CRYPTO_TFM_RES_MASK); 89 return err; 90 } 91 92 static void cts_cbc_crypt_done(struct crypto_async_request *areq, int err) 93 { 94 struct skcipher_request *req = areq->data; 95 96 if (err == -EINPROGRESS) 97 return; 98 99 skcipher_request_complete(req, err); 100 } 101 102 static int cts_cbc_encrypt(struct skcipher_request *req) 103 { 104 struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req); 105 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); 106 struct skcipher_request *subreq = &rctx->subreq; 107 int bsize = crypto_skcipher_blocksize(tfm); 108 u8 d[MAX_CIPHER_BLOCKSIZE * 2] __aligned(__alignof__(u32)); 109 struct scatterlist *sg; 110 unsigned int offset; 111 int lastn; 112 113 offset = rctx->offset; 114 lastn = req->cryptlen - offset; 115 116 sg = scatterwalk_ffwd(rctx->sg, req->dst, offset - bsize); 117 scatterwalk_map_and_copy(d + bsize, sg, 0, bsize, 0); 118 119 memset(d, 0, bsize); 120 scatterwalk_map_and_copy(d, req->src, offset, lastn, 0); 121 122 scatterwalk_map_and_copy(d, sg, 0, bsize + lastn, 1); 123 memzero_explicit(d, sizeof(d)); 124 125 skcipher_request_set_callback(subreq, req->base.flags & 126 CRYPTO_TFM_REQ_MAY_BACKLOG, 127 cts_cbc_crypt_done, req); 128 skcipher_request_set_crypt(subreq, sg, sg, bsize, req->iv); 129 return crypto_skcipher_encrypt(subreq); 130 } 131 132 static void crypto_cts_encrypt_done(struct crypto_async_request *areq, int err) 133 { 134 struct skcipher_request *req = areq->data; 135 136 if (err) 137 goto out; 138 139 err = cts_cbc_encrypt(req); 140 if (err == -EINPROGRESS || err == -EBUSY) 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[MAX_CIPHER_BLOCKSIZE * 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 || err == -EBUSY) 233 return; 234 235 out: 236 skcipher_request_complete(req, err); 237 } 238 239 static int crypto_cts_decrypt(struct skcipher_request *req) 240 { 241 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); 242 struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req); 243 struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm); 244 struct skcipher_request *subreq = &rctx->subreq; 245 int bsize = crypto_skcipher_blocksize(tfm); 246 unsigned int nbytes = req->cryptlen; 247 int cbc_blocks = (nbytes + bsize - 1) / bsize - 1; 248 unsigned int offset; 249 u8 *space; 250 251 skcipher_request_set_tfm(subreq, ctx->child); 252 253 if (cbc_blocks <= 0) { 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 = cbc_blocks * bsize; 268 rctx->offset = offset; 269 270 if (cbc_blocks <= 1) 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 } 282 283 static 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 } 310 311 static 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 } 317 318 static void crypto_cts_free(struct skcipher_instance *inst) 319 { 320 crypto_drop_skcipher(skcipher_instance_ctx(inst)); 321 kfree(inst); 322 } 323 324 static 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 crypto_attr_type *algt; 329 struct skcipher_alg *alg; 330 const char *cipher_name; 331 int err; 332 333 algt = crypto_get_attr_type(tb); 334 if (IS_ERR(algt)) 335 return PTR_ERR(algt); 336 337 if ((algt->type ^ CRYPTO_ALG_TYPE_SKCIPHER) & algt->mask) 338 return -EINVAL; 339 340 cipher_name = crypto_attr_alg_name(tb[1]); 341 if (IS_ERR(cipher_name)) 342 return PTR_ERR(cipher_name); 343 344 inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL); 345 if (!inst) 346 return -ENOMEM; 347 348 spawn = skcipher_instance_ctx(inst); 349 350 crypto_set_skcipher_spawn(spawn, skcipher_crypto_instance(inst)); 351 err = crypto_grab_skcipher(spawn, cipher_name, 0, 352 crypto_requires_sync(algt->type, 353 algt->mask)); 354 if (err) 355 goto err_free_inst; 356 357 alg = crypto_spawn_skcipher_alg(spawn); 358 359 err = -EINVAL; 360 if (crypto_skcipher_alg_ivsize(alg) != alg->base.cra_blocksize) 361 goto err_drop_spawn; 362 363 if (strncmp(alg->base.cra_name, "cbc(", 4)) 364 goto err_drop_spawn; 365 366 err = crypto_inst_setname(skcipher_crypto_instance(inst), "cts", 367 &alg->base); 368 if (err) 369 goto err_drop_spawn; 370 371 inst->alg.base.cra_flags = alg->base.cra_flags & CRYPTO_ALG_ASYNC; 372 inst->alg.base.cra_priority = alg->base.cra_priority; 373 inst->alg.base.cra_blocksize = alg->base.cra_blocksize; 374 inst->alg.base.cra_alignmask = alg->base.cra_alignmask; 375 376 inst->alg.ivsize = alg->base.cra_blocksize; 377 inst->alg.chunksize = crypto_skcipher_alg_chunksize(alg); 378 inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(alg); 379 inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(alg); 380 381 inst->alg.base.cra_ctxsize = sizeof(struct crypto_cts_ctx); 382 383 inst->alg.init = crypto_cts_init_tfm; 384 inst->alg.exit = crypto_cts_exit_tfm; 385 386 inst->alg.setkey = crypto_cts_setkey; 387 inst->alg.encrypt = crypto_cts_encrypt; 388 inst->alg.decrypt = crypto_cts_decrypt; 389 390 inst->free = crypto_cts_free; 391 392 err = skcipher_register_instance(tmpl, inst); 393 if (err) 394 goto err_drop_spawn; 395 396 out: 397 return err; 398 399 err_drop_spawn: 400 crypto_drop_skcipher(spawn); 401 err_free_inst: 402 kfree(inst); 403 goto out; 404 } 405 406 static struct crypto_template crypto_cts_tmpl = { 407 .name = "cts", 408 .create = crypto_cts_create, 409 .module = THIS_MODULE, 410 }; 411 412 static int __init crypto_cts_module_init(void) 413 { 414 return crypto_register_template(&crypto_cts_tmpl); 415 } 416 417 static void __exit crypto_cts_module_exit(void) 418 { 419 crypto_unregister_template(&crypto_cts_tmpl); 420 } 421 422 module_init(crypto_cts_module_init); 423 module_exit(crypto_cts_module_exit); 424 425 MODULE_LICENSE("Dual BSD/GPL"); 426 MODULE_DESCRIPTION("CTS-CBC CipherText Stealing for CBC"); 427 MODULE_ALIAS_CRYPTO("cts"); 428