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 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 return crypto_skcipher_setkey(child, key, keylen); 86 } 87 88 static void cts_cbc_crypt_done(void *data, int err) 89 { 90 struct skcipher_request *req = data; 91 92 if (err == -EINPROGRESS) 93 return; 94 95 skcipher_request_complete(req, err); 96 } 97 98 static int cts_cbc_encrypt(struct skcipher_request *req) 99 { 100 struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req); 101 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); 102 struct skcipher_request *subreq = &rctx->subreq; 103 int bsize = crypto_skcipher_blocksize(tfm); 104 u8 d[MAX_CIPHER_BLOCKSIZE * 2] __aligned(__alignof__(u32)); 105 struct scatterlist *sg; 106 unsigned int offset; 107 int lastn; 108 109 offset = rctx->offset; 110 lastn = req->cryptlen - offset; 111 112 sg = scatterwalk_ffwd(rctx->sg, req->dst, offset - bsize); 113 scatterwalk_map_and_copy(d + bsize, sg, 0, bsize, 0); 114 115 memset(d, 0, bsize); 116 scatterwalk_map_and_copy(d, req->src, offset, lastn, 0); 117 118 scatterwalk_map_and_copy(d, sg, 0, bsize + lastn, 1); 119 memzero_explicit(d, sizeof(d)); 120 121 skcipher_request_set_callback(subreq, req->base.flags & 122 CRYPTO_TFM_REQ_MAY_BACKLOG, 123 cts_cbc_crypt_done, req); 124 skcipher_request_set_crypt(subreq, sg, sg, bsize, req->iv); 125 return crypto_skcipher_encrypt(subreq); 126 } 127 128 static void crypto_cts_encrypt_done(void *data, int err) 129 { 130 struct skcipher_request *req = data; 131 132 if (err) 133 goto out; 134 135 err = cts_cbc_encrypt(req); 136 if (err == -EINPROGRESS || err == -EBUSY) 137 return; 138 139 out: 140 skcipher_request_complete(req, err); 141 } 142 143 static int crypto_cts_encrypt(struct skcipher_request *req) 144 { 145 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); 146 struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req); 147 struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm); 148 struct skcipher_request *subreq = &rctx->subreq; 149 int bsize = crypto_skcipher_blocksize(tfm); 150 unsigned int nbytes = req->cryptlen; 151 unsigned int offset; 152 153 skcipher_request_set_tfm(subreq, ctx->child); 154 155 if (nbytes < bsize) 156 return -EINVAL; 157 158 if (nbytes == bsize) { 159 skcipher_request_set_callback(subreq, req->base.flags, 160 req->base.complete, 161 req->base.data); 162 skcipher_request_set_crypt(subreq, req->src, req->dst, nbytes, 163 req->iv); 164 return crypto_skcipher_encrypt(subreq); 165 } 166 167 offset = rounddown(nbytes - 1, bsize); 168 rctx->offset = offset; 169 170 skcipher_request_set_callback(subreq, req->base.flags, 171 crypto_cts_encrypt_done, req); 172 skcipher_request_set_crypt(subreq, req->src, req->dst, 173 offset, req->iv); 174 175 return crypto_skcipher_encrypt(subreq) ?: 176 cts_cbc_encrypt(req); 177 } 178 179 static int cts_cbc_decrypt(struct skcipher_request *req) 180 { 181 struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req); 182 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); 183 struct skcipher_request *subreq = &rctx->subreq; 184 int bsize = crypto_skcipher_blocksize(tfm); 185 u8 d[MAX_CIPHER_BLOCKSIZE * 2] __aligned(__alignof__(u32)); 186 struct scatterlist *sg; 187 unsigned int offset; 188 u8 *space; 189 int lastn; 190 191 offset = rctx->offset; 192 lastn = req->cryptlen - offset; 193 194 sg = scatterwalk_ffwd(rctx->sg, req->dst, offset - bsize); 195 196 /* 1. Decrypt Cn-1 (s) to create Dn */ 197 scatterwalk_map_and_copy(d + bsize, sg, 0, bsize, 0); 198 space = crypto_cts_reqctx_space(req); 199 crypto_xor(d + bsize, space, bsize); 200 /* 2. Pad Cn with zeros at the end to create C of length BB */ 201 memset(d, 0, bsize); 202 scatterwalk_map_and_copy(d, req->src, offset, lastn, 0); 203 /* 3. Exclusive-or Dn with C to create Xn */ 204 /* 4. Select the first Ln bytes of Xn to create Pn */ 205 crypto_xor(d + bsize, d, lastn); 206 207 /* 5. Append the tail (BB - Ln) bytes of Xn to Cn to create En */ 208 memcpy(d + lastn, d + bsize + lastn, bsize - lastn); 209 /* 6. Decrypt En to create Pn-1 */ 210 211 scatterwalk_map_and_copy(d, sg, 0, bsize + lastn, 1); 212 memzero_explicit(d, sizeof(d)); 213 214 skcipher_request_set_callback(subreq, req->base.flags & 215 CRYPTO_TFM_REQ_MAY_BACKLOG, 216 cts_cbc_crypt_done, req); 217 218 skcipher_request_set_crypt(subreq, sg, sg, bsize, space); 219 return crypto_skcipher_decrypt(subreq); 220 } 221 222 static void crypto_cts_decrypt_done(void *data, int err) 223 { 224 struct skcipher_request *req = data; 225 226 if (err) 227 goto out; 228 229 err = cts_cbc_decrypt(req); 230 if (err == -EINPROGRESS || err == -EBUSY) 231 return; 232 233 out: 234 skcipher_request_complete(req, err); 235 } 236 237 static int crypto_cts_decrypt(struct skcipher_request *req) 238 { 239 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); 240 struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req); 241 struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm); 242 struct skcipher_request *subreq = &rctx->subreq; 243 int bsize = crypto_skcipher_blocksize(tfm); 244 unsigned int nbytes = req->cryptlen; 245 unsigned int offset; 246 u8 *space; 247 248 skcipher_request_set_tfm(subreq, ctx->child); 249 250 if (nbytes < bsize) 251 return -EINVAL; 252 253 if (nbytes == bsize) { 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 = rounddown(nbytes - 1, bsize); 268 rctx->offset = offset; 269 270 if (offset <= bsize) 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_alg_common *alg; 328 struct skcipher_instance *inst; 329 u32 mask; 330 int err; 331 332 err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_SKCIPHER, &mask); 333 if (err) 334 return err; 335 336 inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL); 337 if (!inst) 338 return -ENOMEM; 339 340 spawn = skcipher_instance_ctx(inst); 341 342 err = crypto_grab_skcipher(spawn, skcipher_crypto_instance(inst), 343 crypto_attr_alg_name(tb[1]), 0, mask); 344 if (err) 345 goto err_free_inst; 346 347 alg = crypto_spawn_skcipher_alg_common(spawn); 348 349 err = -EINVAL; 350 if (alg->ivsize != alg->base.cra_blocksize) 351 goto err_free_inst; 352 353 if (strncmp(alg->base.cra_name, "cbc(", 4)) 354 goto err_free_inst; 355 356 err = crypto_inst_setname(skcipher_crypto_instance(inst), "cts", 357 &alg->base); 358 if (err) 359 goto err_free_inst; 360 361 inst->alg.base.cra_priority = alg->base.cra_priority; 362 inst->alg.base.cra_blocksize = alg->base.cra_blocksize; 363 inst->alg.base.cra_alignmask = alg->base.cra_alignmask; 364 365 inst->alg.ivsize = alg->base.cra_blocksize; 366 inst->alg.chunksize = alg->chunksize; 367 inst->alg.min_keysize = alg->min_keysize; 368 inst->alg.max_keysize = alg->max_keysize; 369 370 inst->alg.base.cra_ctxsize = sizeof(struct crypto_cts_ctx); 371 372 inst->alg.init = crypto_cts_init_tfm; 373 inst->alg.exit = crypto_cts_exit_tfm; 374 375 inst->alg.setkey = crypto_cts_setkey; 376 inst->alg.encrypt = crypto_cts_encrypt; 377 inst->alg.decrypt = crypto_cts_decrypt; 378 379 inst->free = crypto_cts_free; 380 381 err = skcipher_register_instance(tmpl, inst); 382 if (err) { 383 err_free_inst: 384 crypto_cts_free(inst); 385 } 386 return err; 387 } 388 389 static struct crypto_template crypto_cts_tmpl = { 390 .name = "cts", 391 .create = crypto_cts_create, 392 .module = THIS_MODULE, 393 }; 394 395 static int __init crypto_cts_module_init(void) 396 { 397 return crypto_register_template(&crypto_cts_tmpl); 398 } 399 400 static void __exit crypto_cts_module_exit(void) 401 { 402 crypto_unregister_template(&crypto_cts_tmpl); 403 } 404 405 subsys_initcall(crypto_cts_module_init); 406 module_exit(crypto_cts_module_exit); 407 408 MODULE_LICENSE("Dual BSD/GPL"); 409 MODULE_DESCRIPTION("CTS-CBC CipherText Stealing for CBC"); 410 MODULE_ALIAS_CRYPTO("cts"); 411