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 53 struct crypto_cts_ctx { 54 struct crypto_skcipher *child; 55 }; 56 57 struct crypto_cts_reqctx { 58 struct scatterlist sg[2]; 59 unsigned offset; 60 struct skcipher_request subreq; 61 }; 62 63 static inline u8 *crypto_cts_reqctx_space(struct skcipher_request *req) 64 { 65 struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req); 66 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); 67 struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm); 68 struct crypto_skcipher *child = ctx->child; 69 70 return PTR_ALIGN((u8 *)(rctx + 1) + crypto_skcipher_reqsize(child), 71 crypto_skcipher_alignmask(tfm) + 1); 72 } 73 74 static int crypto_cts_setkey(struct crypto_skcipher *parent, const u8 *key, 75 unsigned int keylen) 76 { 77 struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(parent); 78 struct crypto_skcipher *child = ctx->child; 79 int err; 80 81 crypto_skcipher_clear_flags(child, CRYPTO_TFM_REQ_MASK); 82 crypto_skcipher_set_flags(child, crypto_skcipher_get_flags(parent) & 83 CRYPTO_TFM_REQ_MASK); 84 err = crypto_skcipher_setkey(child, key, keylen); 85 crypto_skcipher_set_flags(parent, crypto_skcipher_get_flags(child) & 86 CRYPTO_TFM_RES_MASK); 87 return err; 88 } 89 90 static void cts_cbc_crypt_done(struct crypto_async_request *areq, int err) 91 { 92 struct skcipher_request *req = areq->data; 93 94 if (err == -EINPROGRESS) 95 return; 96 97 skcipher_request_complete(req, err); 98 } 99 100 static int cts_cbc_encrypt(struct skcipher_request *req) 101 { 102 struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req); 103 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); 104 struct skcipher_request *subreq = &rctx->subreq; 105 int bsize = crypto_skcipher_blocksize(tfm); 106 u8 d[bsize * 2] __attribute__ ((aligned(__alignof__(u32)))); 107 struct scatterlist *sg; 108 unsigned int offset; 109 int lastn; 110 111 offset = rctx->offset; 112 lastn = req->cryptlen - offset; 113 114 sg = scatterwalk_ffwd(rctx->sg, req->dst, offset - bsize); 115 scatterwalk_map_and_copy(d + bsize, sg, 0, bsize, 0); 116 117 memset(d, 0, bsize); 118 scatterwalk_map_and_copy(d, req->src, offset, lastn, 0); 119 120 scatterwalk_map_and_copy(d, sg, 0, bsize + lastn, 1); 121 memzero_explicit(d, sizeof(d)); 122 123 skcipher_request_set_callback(subreq, req->base.flags & 124 CRYPTO_TFM_REQ_MAY_BACKLOG, 125 cts_cbc_crypt_done, req); 126 skcipher_request_set_crypt(subreq, sg, sg, bsize, req->iv); 127 return crypto_skcipher_encrypt(subreq); 128 } 129 130 static void crypto_cts_encrypt_done(struct crypto_async_request *areq, int err) 131 { 132 struct skcipher_request *req = areq->data; 133 134 if (err) 135 goto out; 136 137 err = cts_cbc_encrypt(req); 138 if (err == -EINPROGRESS || 139 (err == -EBUSY && req->base.flags & CRYPTO_TFM_REQ_MAY_BACKLOG)) 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] __attribute__ ((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 || 232 (err == -EBUSY && req->base.flags & CRYPTO_TFM_REQ_MAY_BACKLOG)) 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_skcipher2(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_skcipher2(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 /* We access the data as u32s when xoring. */ 377 inst->alg.base.cra_alignmask |= __alignof__(u32) - 1; 378 379 inst->alg.ivsize = alg->base.cra_blocksize; 380 inst->alg.chunksize = crypto_skcipher_alg_chunksize(alg); 381 inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(alg); 382 inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(alg); 383 384 inst->alg.base.cra_ctxsize = sizeof(struct crypto_cts_ctx); 385 386 inst->alg.init = crypto_cts_init_tfm; 387 inst->alg.exit = crypto_cts_exit_tfm; 388 389 inst->alg.setkey = crypto_cts_setkey; 390 inst->alg.encrypt = crypto_cts_encrypt; 391 inst->alg.decrypt = crypto_cts_decrypt; 392 393 inst->free = crypto_cts_free; 394 395 err = skcipher_register_instance(tmpl, inst); 396 if (err) 397 goto err_drop_spawn; 398 399 out: 400 return err; 401 402 err_drop_spawn: 403 crypto_drop_skcipher(spawn); 404 err_free_inst: 405 kfree(inst); 406 goto out; 407 } 408 409 static struct crypto_template crypto_cts_tmpl = { 410 .name = "cts", 411 .create = crypto_cts_create, 412 .module = THIS_MODULE, 413 }; 414 415 static int __init crypto_cts_module_init(void) 416 { 417 return crypto_register_template(&crypto_cts_tmpl); 418 } 419 420 static void __exit crypto_cts_module_exit(void) 421 { 422 crypto_unregister_template(&crypto_cts_tmpl); 423 } 424 425 module_init(crypto_cts_module_init); 426 module_exit(crypto_cts_module_exit); 427 428 MODULE_LICENSE("Dual BSD/GPL"); 429 MODULE_DESCRIPTION("CTS-CBC CipherText Stealing for CBC"); 430 MODULE_ALIAS_CRYPTO("cts"); 431