1 /* 2 * Key Wrapping: RFC3394 / NIST SP800-38F 3 * 4 * Copyright (C) 2015, Stephan Mueller <smueller@chronox.de> 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, and the entire permission notice in its entirety, 11 * including the disclaimer of warranties. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 3. The name of the author may not be used to endorse or promote 16 * products derived from this software without specific prior 17 * written permission. 18 * 19 * ALTERNATIVELY, this product may be distributed under the terms of 20 * the GNU General Public License, in which case the provisions of the GPL2 21 * are required INSTEAD OF the above restrictions. (This clause is 22 * necessary due to a potential bad interaction between the GPL and 23 * the restrictions contained in a BSD-style copyright.) 24 * 25 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED 26 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 27 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF 28 * WHICH ARE HEREBY DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE 29 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 30 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT 31 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR 32 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF 33 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 34 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE 35 * USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH 36 * DAMAGE. 37 */ 38 39 /* 40 * Note for using key wrapping: 41 * 42 * * The result of the encryption operation is the ciphertext starting 43 * with the 2nd semiblock. The first semiblock is provided as the IV. 44 * The IV used to start the encryption operation is the default IV. 45 * 46 * * The input for the decryption is the first semiblock handed in as an 47 * IV. The ciphertext is the data starting with the 2nd semiblock. The 48 * return code of the decryption operation will be EBADMSG in case an 49 * integrity error occurs. 50 * 51 * To obtain the full result of an encryption as expected by SP800-38F, the 52 * caller must allocate a buffer of plaintext + 8 bytes: 53 * 54 * unsigned int datalen = ptlen + crypto_skcipher_ivsize(tfm); 55 * u8 data[datalen]; 56 * u8 *iv = data; 57 * u8 *pt = data + crypto_skcipher_ivsize(tfm); 58 * <ensure that pt contains the plaintext of size ptlen> 59 * sg_init_one(&sg, ptdata, ptlen); 60 * skcipher_request_set_crypt(req, &sg, &sg, ptlen, iv); 61 * 62 * ==> After encryption, data now contains full KW result as per SP800-38F. 63 * 64 * In case of decryption, ciphertext now already has the expected length 65 * and must be segmented appropriately: 66 * 67 * unsigned int datalen = CTLEN; 68 * u8 data[datalen]; 69 * <ensure that data contains full ciphertext> 70 * u8 *iv = data; 71 * u8 *ct = data + crypto_skcipher_ivsize(tfm); 72 * unsigned int ctlen = datalen - crypto_skcipher_ivsize(tfm); 73 * sg_init_one(&sg, ctdata, ctlen); 74 * skcipher_request_set_crypt(req, &sg, &sg, ptlen, iv); 75 * 76 * ==> After decryption (which hopefully does not return EBADMSG), the ct 77 * pointer now points to the plaintext of size ctlen. 78 * 79 * Note 2: KWP is not implemented as this would defy in-place operation. 80 * If somebody wants to wrap non-aligned data, he should simply pad 81 * the input with zeros to fill it up to the 8 byte boundary. 82 */ 83 84 #include <linux/module.h> 85 #include <linux/crypto.h> 86 #include <linux/scatterlist.h> 87 #include <crypto/scatterwalk.h> 88 #include <crypto/internal/skcipher.h> 89 90 struct crypto_kw_ctx { 91 struct crypto_cipher *child; 92 }; 93 94 struct crypto_kw_block { 95 #define SEMIBSIZE 8 96 u8 A[SEMIBSIZE]; 97 u8 R[SEMIBSIZE]; 98 }; 99 100 /* convert 64 bit integer into its string representation */ 101 static inline void crypto_kw_cpu_to_be64(u64 val, u8 *buf) 102 { 103 __be64 *a = (__be64 *)buf; 104 105 *a = cpu_to_be64(val); 106 } 107 108 /* 109 * Fast forward the SGL to the "end" length minus SEMIBSIZE. 110 * The start in the SGL defined by the fast-forward is returned with 111 * the walk variable 112 */ 113 static void crypto_kw_scatterlist_ff(struct scatter_walk *walk, 114 struct scatterlist *sg, 115 unsigned int end) 116 { 117 unsigned int skip = 0; 118 119 /* The caller should only operate on full SEMIBLOCKs. */ 120 BUG_ON(end < SEMIBSIZE); 121 122 skip = end - SEMIBSIZE; 123 while (sg) { 124 if (sg->length > skip) { 125 scatterwalk_start(walk, sg); 126 scatterwalk_advance(walk, skip); 127 break; 128 } else 129 skip -= sg->length; 130 131 sg = sg_next(sg); 132 } 133 } 134 135 static int crypto_kw_decrypt(struct blkcipher_desc *desc, 136 struct scatterlist *dst, struct scatterlist *src, 137 unsigned int nbytes) 138 { 139 struct crypto_blkcipher *tfm = desc->tfm; 140 struct crypto_kw_ctx *ctx = crypto_blkcipher_ctx(tfm); 141 struct crypto_cipher *child = ctx->child; 142 143 unsigned long alignmask = max_t(unsigned long, SEMIBSIZE, 144 crypto_cipher_alignmask(child)); 145 unsigned int i; 146 147 u8 blockbuf[sizeof(struct crypto_kw_block) + alignmask]; 148 struct crypto_kw_block *block = (struct crypto_kw_block *) 149 PTR_ALIGN(blockbuf + 0, alignmask + 1); 150 151 u64 t = 6 * ((nbytes) >> 3); 152 struct scatterlist *lsrc, *ldst; 153 int ret = 0; 154 155 /* 156 * Require at least 2 semiblocks (note, the 3rd semiblock that is 157 * required by SP800-38F is the IV. 158 */ 159 if (nbytes < (2 * SEMIBSIZE) || nbytes % SEMIBSIZE) 160 return -EINVAL; 161 162 /* Place the IV into block A */ 163 memcpy(block->A, desc->info, SEMIBSIZE); 164 165 /* 166 * src scatterlist is read-only. dst scatterlist is r/w. During the 167 * first loop, lsrc points to src and ldst to dst. For any 168 * subsequent round, the code operates on dst only. 169 */ 170 lsrc = src; 171 ldst = dst; 172 173 for (i = 0; i < 6; i++) { 174 u8 tbe_buffer[SEMIBSIZE + alignmask]; 175 /* alignment for the crypto_xor and the _to_be64 operation */ 176 u8 *tbe = PTR_ALIGN(tbe_buffer + 0, alignmask + 1); 177 unsigned int tmp_nbytes = nbytes; 178 struct scatter_walk src_walk, dst_walk; 179 180 while (tmp_nbytes) { 181 /* move pointer by tmp_nbytes in the SGL */ 182 crypto_kw_scatterlist_ff(&src_walk, lsrc, tmp_nbytes); 183 /* get the source block */ 184 scatterwalk_copychunks(block->R, &src_walk, SEMIBSIZE, 185 false); 186 187 /* perform KW operation: get counter as byte string */ 188 crypto_kw_cpu_to_be64(t, tbe); 189 /* perform KW operation: modify IV with counter */ 190 crypto_xor(block->A, tbe, SEMIBSIZE); 191 t--; 192 /* perform KW operation: decrypt block */ 193 crypto_cipher_decrypt_one(child, (u8*)block, 194 (u8*)block); 195 196 /* move pointer by tmp_nbytes in the SGL */ 197 crypto_kw_scatterlist_ff(&dst_walk, ldst, tmp_nbytes); 198 /* Copy block->R into place */ 199 scatterwalk_copychunks(block->R, &dst_walk, SEMIBSIZE, 200 true); 201 202 tmp_nbytes -= SEMIBSIZE; 203 } 204 205 /* we now start to operate on the dst SGL only */ 206 lsrc = dst; 207 ldst = dst; 208 } 209 210 /* Perform authentication check */ 211 if (crypto_memneq("\xA6\xA6\xA6\xA6\xA6\xA6\xA6\xA6", block->A, 212 SEMIBSIZE)) 213 ret = -EBADMSG; 214 215 memzero_explicit(block, sizeof(struct crypto_kw_block)); 216 217 return ret; 218 } 219 220 static int crypto_kw_encrypt(struct blkcipher_desc *desc, 221 struct scatterlist *dst, struct scatterlist *src, 222 unsigned int nbytes) 223 { 224 struct crypto_blkcipher *tfm = desc->tfm; 225 struct crypto_kw_ctx *ctx = crypto_blkcipher_ctx(tfm); 226 struct crypto_cipher *child = ctx->child; 227 228 unsigned long alignmask = max_t(unsigned long, SEMIBSIZE, 229 crypto_cipher_alignmask(child)); 230 unsigned int i; 231 232 u8 blockbuf[sizeof(struct crypto_kw_block) + alignmask]; 233 struct crypto_kw_block *block = (struct crypto_kw_block *) 234 PTR_ALIGN(blockbuf + 0, alignmask + 1); 235 236 u64 t = 1; 237 struct scatterlist *lsrc, *ldst; 238 239 /* 240 * Require at least 2 semiblocks (note, the 3rd semiblock that is 241 * required by SP800-38F is the IV that occupies the first semiblock. 242 * This means that the dst memory must be one semiblock larger than src. 243 * Also ensure that the given data is aligned to semiblock. 244 */ 245 if (nbytes < (2 * SEMIBSIZE) || nbytes % SEMIBSIZE) 246 return -EINVAL; 247 248 /* 249 * Place the predefined IV into block A -- for encrypt, the caller 250 * does not need to provide an IV, but he needs to fetch the final IV. 251 */ 252 memcpy(block->A, "\xA6\xA6\xA6\xA6\xA6\xA6\xA6\xA6", SEMIBSIZE); 253 254 /* 255 * src scatterlist is read-only. dst scatterlist is r/w. During the 256 * first loop, lsrc points to src and ldst to dst. For any 257 * subsequent round, the code operates on dst only. 258 */ 259 lsrc = src; 260 ldst = dst; 261 262 for (i = 0; i < 6; i++) { 263 u8 tbe_buffer[SEMIBSIZE + alignmask]; 264 u8 *tbe = PTR_ALIGN(tbe_buffer + 0, alignmask + 1); 265 unsigned int tmp_nbytes = nbytes; 266 struct scatter_walk src_walk, dst_walk; 267 268 scatterwalk_start(&src_walk, lsrc); 269 scatterwalk_start(&dst_walk, ldst); 270 271 while (tmp_nbytes) { 272 /* get the source block */ 273 scatterwalk_copychunks(block->R, &src_walk, SEMIBSIZE, 274 false); 275 276 /* perform KW operation: encrypt block */ 277 crypto_cipher_encrypt_one(child, (u8 *)block, 278 (u8 *)block); 279 /* perform KW operation: get counter as byte string */ 280 crypto_kw_cpu_to_be64(t, tbe); 281 /* perform KW operation: modify IV with counter */ 282 crypto_xor(block->A, tbe, SEMIBSIZE); 283 t++; 284 285 /* Copy block->R into place */ 286 scatterwalk_copychunks(block->R, &dst_walk, SEMIBSIZE, 287 true); 288 289 tmp_nbytes -= SEMIBSIZE; 290 } 291 292 /* we now start to operate on the dst SGL only */ 293 lsrc = dst; 294 ldst = dst; 295 } 296 297 /* establish the IV for the caller to pick up */ 298 memcpy(desc->info, block->A, SEMIBSIZE); 299 300 memzero_explicit(block, sizeof(struct crypto_kw_block)); 301 302 return 0; 303 } 304 305 static int crypto_kw_setkey(struct crypto_tfm *parent, const u8 *key, 306 unsigned int keylen) 307 { 308 struct crypto_kw_ctx *ctx = crypto_tfm_ctx(parent); 309 struct crypto_cipher *child = ctx->child; 310 int err; 311 312 crypto_cipher_clear_flags(child, CRYPTO_TFM_REQ_MASK); 313 crypto_cipher_set_flags(child, crypto_tfm_get_flags(parent) & 314 CRYPTO_TFM_REQ_MASK); 315 err = crypto_cipher_setkey(child, key, keylen); 316 crypto_tfm_set_flags(parent, crypto_cipher_get_flags(child) & 317 CRYPTO_TFM_RES_MASK); 318 return err; 319 } 320 321 static int crypto_kw_init_tfm(struct crypto_tfm *tfm) 322 { 323 struct crypto_instance *inst = crypto_tfm_alg_instance(tfm); 324 struct crypto_spawn *spawn = crypto_instance_ctx(inst); 325 struct crypto_kw_ctx *ctx = crypto_tfm_ctx(tfm); 326 struct crypto_cipher *cipher; 327 328 cipher = crypto_spawn_cipher(spawn); 329 if (IS_ERR(cipher)) 330 return PTR_ERR(cipher); 331 332 ctx->child = cipher; 333 return 0; 334 } 335 336 static void crypto_kw_exit_tfm(struct crypto_tfm *tfm) 337 { 338 struct crypto_kw_ctx *ctx = crypto_tfm_ctx(tfm); 339 340 crypto_free_cipher(ctx->child); 341 } 342 343 static struct crypto_instance *crypto_kw_alloc(struct rtattr **tb) 344 { 345 struct crypto_instance *inst = NULL; 346 struct crypto_alg *alg = NULL; 347 int err; 348 349 err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_BLKCIPHER); 350 if (err) 351 return ERR_PTR(err); 352 353 alg = crypto_get_attr_alg(tb, CRYPTO_ALG_TYPE_CIPHER, 354 CRYPTO_ALG_TYPE_MASK); 355 if (IS_ERR(alg)) 356 return ERR_CAST(alg); 357 358 inst = ERR_PTR(-EINVAL); 359 /* Section 5.1 requirement for KW */ 360 if (alg->cra_blocksize != sizeof(struct crypto_kw_block)) 361 goto err; 362 363 inst = crypto_alloc_instance("kw", alg); 364 if (IS_ERR(inst)) 365 goto err; 366 367 inst->alg.cra_flags = CRYPTO_ALG_TYPE_BLKCIPHER; 368 inst->alg.cra_priority = alg->cra_priority; 369 inst->alg.cra_blocksize = SEMIBSIZE; 370 inst->alg.cra_alignmask = 0; 371 inst->alg.cra_type = &crypto_blkcipher_type; 372 inst->alg.cra_blkcipher.ivsize = SEMIBSIZE; 373 inst->alg.cra_blkcipher.min_keysize = alg->cra_cipher.cia_min_keysize; 374 inst->alg.cra_blkcipher.max_keysize = alg->cra_cipher.cia_max_keysize; 375 376 inst->alg.cra_ctxsize = sizeof(struct crypto_kw_ctx); 377 378 inst->alg.cra_init = crypto_kw_init_tfm; 379 inst->alg.cra_exit = crypto_kw_exit_tfm; 380 381 inst->alg.cra_blkcipher.setkey = crypto_kw_setkey; 382 inst->alg.cra_blkcipher.encrypt = crypto_kw_encrypt; 383 inst->alg.cra_blkcipher.decrypt = crypto_kw_decrypt; 384 385 err: 386 crypto_mod_put(alg); 387 return inst; 388 } 389 390 static void crypto_kw_free(struct crypto_instance *inst) 391 { 392 crypto_drop_spawn(crypto_instance_ctx(inst)); 393 kfree(inst); 394 } 395 396 static struct crypto_template crypto_kw_tmpl = { 397 .name = "kw", 398 .alloc = crypto_kw_alloc, 399 .free = crypto_kw_free, 400 .module = THIS_MODULE, 401 }; 402 403 static int __init crypto_kw_init(void) 404 { 405 return crypto_register_template(&crypto_kw_tmpl); 406 } 407 408 static void __exit crypto_kw_exit(void) 409 { 410 crypto_unregister_template(&crypto_kw_tmpl); 411 } 412 413 module_init(crypto_kw_init); 414 module_exit(crypto_kw_exit); 415 416 MODULE_LICENSE("Dual BSD/GPL"); 417 MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>"); 418 MODULE_DESCRIPTION("Key Wrapping (RFC3394 / NIST SP800-38F)"); 419 MODULE_ALIAS_CRYPTO("kw"); 420