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 __be64 A; 97 __be64 R; 98 }; 99 100 /* 101 * Fast forward the SGL to the "end" length minus SEMIBSIZE. 102 * The start in the SGL defined by the fast-forward is returned with 103 * the walk variable 104 */ 105 static void crypto_kw_scatterlist_ff(struct scatter_walk *walk, 106 struct scatterlist *sg, 107 unsigned int end) 108 { 109 unsigned int skip = 0; 110 111 /* The caller should only operate on full SEMIBLOCKs. */ 112 BUG_ON(end < SEMIBSIZE); 113 114 skip = end - SEMIBSIZE; 115 while (sg) { 116 if (sg->length > skip) { 117 scatterwalk_start(walk, sg); 118 scatterwalk_advance(walk, skip); 119 break; 120 } else 121 skip -= sg->length; 122 123 sg = sg_next(sg); 124 } 125 } 126 127 static int crypto_kw_decrypt(struct blkcipher_desc *desc, 128 struct scatterlist *dst, struct scatterlist *src, 129 unsigned int nbytes) 130 { 131 struct crypto_blkcipher *tfm = desc->tfm; 132 struct crypto_kw_ctx *ctx = crypto_blkcipher_ctx(tfm); 133 struct crypto_cipher *child = ctx->child; 134 struct crypto_kw_block block; 135 struct scatterlist *lsrc, *ldst; 136 u64 t = 6 * ((nbytes) >> 3); 137 unsigned int i; 138 int ret = 0; 139 140 /* 141 * Require at least 2 semiblocks (note, the 3rd semiblock that is 142 * required by SP800-38F is the IV. 143 */ 144 if (nbytes < (2 * SEMIBSIZE) || nbytes % SEMIBSIZE) 145 return -EINVAL; 146 147 /* Place the IV into block A */ 148 memcpy(&block.A, desc->info, SEMIBSIZE); 149 150 /* 151 * src scatterlist is read-only. dst scatterlist is r/w. During the 152 * first loop, lsrc points to src and ldst to dst. For any 153 * subsequent round, the code operates on dst only. 154 */ 155 lsrc = src; 156 ldst = dst; 157 158 for (i = 0; i < 6; i++) { 159 struct scatter_walk src_walk, dst_walk; 160 unsigned int tmp_nbytes = nbytes; 161 162 while (tmp_nbytes) { 163 /* move pointer by tmp_nbytes in the SGL */ 164 crypto_kw_scatterlist_ff(&src_walk, lsrc, tmp_nbytes); 165 /* get the source block */ 166 scatterwalk_copychunks(&block.R, &src_walk, SEMIBSIZE, 167 false); 168 169 /* perform KW operation: modify IV with counter */ 170 block.A ^= cpu_to_be64(t); 171 t--; 172 /* perform KW operation: decrypt block */ 173 crypto_cipher_decrypt_one(child, (u8*)&block, 174 (u8*)&block); 175 176 /* move pointer by tmp_nbytes in the SGL */ 177 crypto_kw_scatterlist_ff(&dst_walk, ldst, tmp_nbytes); 178 /* Copy block->R into place */ 179 scatterwalk_copychunks(&block.R, &dst_walk, SEMIBSIZE, 180 true); 181 182 tmp_nbytes -= SEMIBSIZE; 183 } 184 185 /* we now start to operate on the dst SGL only */ 186 lsrc = dst; 187 ldst = dst; 188 } 189 190 /* Perform authentication check */ 191 if (block.A != cpu_to_be64(0xa6a6a6a6a6a6a6a6ULL)) 192 ret = -EBADMSG; 193 194 memzero_explicit(&block, sizeof(struct crypto_kw_block)); 195 196 return ret; 197 } 198 199 static int crypto_kw_encrypt(struct blkcipher_desc *desc, 200 struct scatterlist *dst, struct scatterlist *src, 201 unsigned int nbytes) 202 { 203 struct crypto_blkcipher *tfm = desc->tfm; 204 struct crypto_kw_ctx *ctx = crypto_blkcipher_ctx(tfm); 205 struct crypto_cipher *child = ctx->child; 206 struct crypto_kw_block block; 207 struct scatterlist *lsrc, *ldst; 208 u64 t = 1; 209 unsigned int i; 210 211 /* 212 * Require at least 2 semiblocks (note, the 3rd semiblock that is 213 * required by SP800-38F is the IV that occupies the first semiblock. 214 * This means that the dst memory must be one semiblock larger than src. 215 * Also ensure that the given data is aligned to semiblock. 216 */ 217 if (nbytes < (2 * SEMIBSIZE) || nbytes % SEMIBSIZE) 218 return -EINVAL; 219 220 /* 221 * Place the predefined IV into block A -- for encrypt, the caller 222 * does not need to provide an IV, but he needs to fetch the final IV. 223 */ 224 block.A = cpu_to_be64(0xa6a6a6a6a6a6a6a6ULL); 225 226 /* 227 * src scatterlist is read-only. dst scatterlist is r/w. During the 228 * first loop, lsrc points to src and ldst to dst. For any 229 * subsequent round, the code operates on dst only. 230 */ 231 lsrc = src; 232 ldst = dst; 233 234 for (i = 0; i < 6; i++) { 235 struct scatter_walk src_walk, dst_walk; 236 unsigned int tmp_nbytes = nbytes; 237 238 scatterwalk_start(&src_walk, lsrc); 239 scatterwalk_start(&dst_walk, ldst); 240 241 while (tmp_nbytes) { 242 /* get the source block */ 243 scatterwalk_copychunks(&block.R, &src_walk, SEMIBSIZE, 244 false); 245 246 /* perform KW operation: encrypt block */ 247 crypto_cipher_encrypt_one(child, (u8 *)&block, 248 (u8 *)&block); 249 /* perform KW operation: modify IV with counter */ 250 block.A ^= cpu_to_be64(t); 251 t++; 252 253 /* Copy block->R into place */ 254 scatterwalk_copychunks(&block.R, &dst_walk, SEMIBSIZE, 255 true); 256 257 tmp_nbytes -= SEMIBSIZE; 258 } 259 260 /* we now start to operate on the dst SGL only */ 261 lsrc = dst; 262 ldst = dst; 263 } 264 265 /* establish the IV for the caller to pick up */ 266 memcpy(desc->info, &block.A, SEMIBSIZE); 267 268 memzero_explicit(&block, sizeof(struct crypto_kw_block)); 269 270 return 0; 271 } 272 273 static int crypto_kw_setkey(struct crypto_tfm *parent, const u8 *key, 274 unsigned int keylen) 275 { 276 struct crypto_kw_ctx *ctx = crypto_tfm_ctx(parent); 277 struct crypto_cipher *child = ctx->child; 278 int err; 279 280 crypto_cipher_clear_flags(child, CRYPTO_TFM_REQ_MASK); 281 crypto_cipher_set_flags(child, crypto_tfm_get_flags(parent) & 282 CRYPTO_TFM_REQ_MASK); 283 err = crypto_cipher_setkey(child, key, keylen); 284 crypto_tfm_set_flags(parent, crypto_cipher_get_flags(child) & 285 CRYPTO_TFM_RES_MASK); 286 return err; 287 } 288 289 static int crypto_kw_init_tfm(struct crypto_tfm *tfm) 290 { 291 struct crypto_instance *inst = crypto_tfm_alg_instance(tfm); 292 struct crypto_spawn *spawn = crypto_instance_ctx(inst); 293 struct crypto_kw_ctx *ctx = crypto_tfm_ctx(tfm); 294 struct crypto_cipher *cipher; 295 296 cipher = crypto_spawn_cipher(spawn); 297 if (IS_ERR(cipher)) 298 return PTR_ERR(cipher); 299 300 ctx->child = cipher; 301 return 0; 302 } 303 304 static void crypto_kw_exit_tfm(struct crypto_tfm *tfm) 305 { 306 struct crypto_kw_ctx *ctx = crypto_tfm_ctx(tfm); 307 308 crypto_free_cipher(ctx->child); 309 } 310 311 static struct crypto_instance *crypto_kw_alloc(struct rtattr **tb) 312 { 313 struct crypto_instance *inst = NULL; 314 struct crypto_alg *alg = NULL; 315 int err; 316 317 err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_BLKCIPHER); 318 if (err) 319 return ERR_PTR(err); 320 321 alg = crypto_get_attr_alg(tb, CRYPTO_ALG_TYPE_CIPHER, 322 CRYPTO_ALG_TYPE_MASK); 323 if (IS_ERR(alg)) 324 return ERR_CAST(alg); 325 326 inst = ERR_PTR(-EINVAL); 327 /* Section 5.1 requirement for KW */ 328 if (alg->cra_blocksize != sizeof(struct crypto_kw_block)) 329 goto err; 330 331 inst = crypto_alloc_instance("kw", alg); 332 if (IS_ERR(inst)) 333 goto err; 334 335 inst->alg.cra_flags = CRYPTO_ALG_TYPE_BLKCIPHER; 336 inst->alg.cra_priority = alg->cra_priority; 337 inst->alg.cra_blocksize = SEMIBSIZE; 338 inst->alg.cra_alignmask = 0; 339 inst->alg.cra_type = &crypto_blkcipher_type; 340 inst->alg.cra_blkcipher.ivsize = SEMIBSIZE; 341 inst->alg.cra_blkcipher.min_keysize = alg->cra_cipher.cia_min_keysize; 342 inst->alg.cra_blkcipher.max_keysize = alg->cra_cipher.cia_max_keysize; 343 344 inst->alg.cra_ctxsize = sizeof(struct crypto_kw_ctx); 345 346 inst->alg.cra_init = crypto_kw_init_tfm; 347 inst->alg.cra_exit = crypto_kw_exit_tfm; 348 349 inst->alg.cra_blkcipher.setkey = crypto_kw_setkey; 350 inst->alg.cra_blkcipher.encrypt = crypto_kw_encrypt; 351 inst->alg.cra_blkcipher.decrypt = crypto_kw_decrypt; 352 353 err: 354 crypto_mod_put(alg); 355 return inst; 356 } 357 358 static void crypto_kw_free(struct crypto_instance *inst) 359 { 360 crypto_drop_spawn(crypto_instance_ctx(inst)); 361 kfree(inst); 362 } 363 364 static struct crypto_template crypto_kw_tmpl = { 365 .name = "kw", 366 .alloc = crypto_kw_alloc, 367 .free = crypto_kw_free, 368 .module = THIS_MODULE, 369 }; 370 371 static int __init crypto_kw_init(void) 372 { 373 return crypto_register_template(&crypto_kw_tmpl); 374 } 375 376 static void __exit crypto_kw_exit(void) 377 { 378 crypto_unregister_template(&crypto_kw_tmpl); 379 } 380 381 module_init(crypto_kw_init); 382 module_exit(crypto_kw_exit); 383 384 MODULE_LICENSE("Dual BSD/GPL"); 385 MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>"); 386 MODULE_DESCRIPTION("Key Wrapping (RFC3394 / NIST SP800-38F)"); 387 MODULE_ALIAS_CRYPTO("kw"); 388