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, pt, 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, ct, ctlen); 74 * skcipher_request_set_crypt(req, &sg, &sg, ctlen, 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/cipher.h> 89 #include <crypto/internal/skcipher.h> 90 91 struct crypto_kw_block { 92 #define SEMIBSIZE 8 93 __be64 A; 94 __be64 R; 95 }; 96 97 /* 98 * Fast forward the SGL to the "end" length minus SEMIBSIZE. 99 * The start in the SGL defined by the fast-forward is returned with 100 * the walk variable 101 */ 102 static void crypto_kw_scatterlist_ff(struct scatter_walk *walk, 103 struct scatterlist *sg, 104 unsigned int end) 105 { 106 unsigned int skip = 0; 107 108 /* The caller should only operate on full SEMIBLOCKs. */ 109 BUG_ON(end < SEMIBSIZE); 110 111 skip = end - SEMIBSIZE; 112 while (sg) { 113 if (sg->length > skip) { 114 scatterwalk_start(walk, sg); 115 scatterwalk_advance(walk, skip); 116 break; 117 } 118 119 skip -= sg->length; 120 sg = sg_next(sg); 121 } 122 } 123 124 static int crypto_kw_decrypt(struct skcipher_request *req) 125 { 126 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); 127 struct crypto_cipher *cipher = skcipher_cipher_simple(tfm); 128 struct crypto_kw_block block; 129 struct scatterlist *src, *dst; 130 u64 t = 6 * ((req->cryptlen) >> 3); 131 unsigned int i; 132 int ret = 0; 133 134 /* 135 * Require at least 2 semiblocks (note, the 3rd semiblock that is 136 * required by SP800-38F is the IV. 137 */ 138 if (req->cryptlen < (2 * SEMIBSIZE) || req->cryptlen % SEMIBSIZE) 139 return -EINVAL; 140 141 /* Place the IV into block A */ 142 memcpy(&block.A, req->iv, SEMIBSIZE); 143 144 /* 145 * src scatterlist is read-only. dst scatterlist is r/w. During the 146 * first loop, src points to req->src and dst to req->dst. For any 147 * subsequent round, the code operates on req->dst only. 148 */ 149 src = req->src; 150 dst = req->dst; 151 152 for (i = 0; i < 6; i++) { 153 struct scatter_walk src_walk, dst_walk; 154 unsigned int nbytes = req->cryptlen; 155 156 while (nbytes) { 157 /* move pointer by nbytes in the SGL */ 158 crypto_kw_scatterlist_ff(&src_walk, src, nbytes); 159 /* get the source block */ 160 scatterwalk_copychunks(&block.R, &src_walk, SEMIBSIZE, 161 false); 162 163 /* perform KW operation: modify IV with counter */ 164 block.A ^= cpu_to_be64(t); 165 t--; 166 /* perform KW operation: decrypt block */ 167 crypto_cipher_decrypt_one(cipher, (u8 *)&block, 168 (u8 *)&block); 169 170 /* move pointer by nbytes in the SGL */ 171 crypto_kw_scatterlist_ff(&dst_walk, dst, nbytes); 172 /* Copy block->R into place */ 173 scatterwalk_copychunks(&block.R, &dst_walk, SEMIBSIZE, 174 true); 175 176 nbytes -= SEMIBSIZE; 177 } 178 179 /* we now start to operate on the dst SGL only */ 180 src = req->dst; 181 dst = req->dst; 182 } 183 184 /* Perform authentication check */ 185 if (block.A != cpu_to_be64(0xa6a6a6a6a6a6a6a6ULL)) 186 ret = -EBADMSG; 187 188 memzero_explicit(&block, sizeof(struct crypto_kw_block)); 189 190 return ret; 191 } 192 193 static int crypto_kw_encrypt(struct skcipher_request *req) 194 { 195 struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); 196 struct crypto_cipher *cipher = skcipher_cipher_simple(tfm); 197 struct crypto_kw_block block; 198 struct scatterlist *src, *dst; 199 u64 t = 1; 200 unsigned int i; 201 202 /* 203 * Require at least 2 semiblocks (note, the 3rd semiblock that is 204 * required by SP800-38F is the IV that occupies the first semiblock. 205 * This means that the dst memory must be one semiblock larger than src. 206 * Also ensure that the given data is aligned to semiblock. 207 */ 208 if (req->cryptlen < (2 * SEMIBSIZE) || req->cryptlen % SEMIBSIZE) 209 return -EINVAL; 210 211 /* 212 * Place the predefined IV into block A -- for encrypt, the caller 213 * does not need to provide an IV, but he needs to fetch the final IV. 214 */ 215 block.A = cpu_to_be64(0xa6a6a6a6a6a6a6a6ULL); 216 217 /* 218 * src scatterlist is read-only. dst scatterlist is r/w. During the 219 * first loop, src points to req->src and dst to req->dst. For any 220 * subsequent round, the code operates on req->dst only. 221 */ 222 src = req->src; 223 dst = req->dst; 224 225 for (i = 0; i < 6; i++) { 226 struct scatter_walk src_walk, dst_walk; 227 unsigned int nbytes = req->cryptlen; 228 229 scatterwalk_start(&src_walk, src); 230 scatterwalk_start(&dst_walk, dst); 231 232 while (nbytes) { 233 /* get the source block */ 234 scatterwalk_copychunks(&block.R, &src_walk, SEMIBSIZE, 235 false); 236 237 /* perform KW operation: encrypt block */ 238 crypto_cipher_encrypt_one(cipher, (u8 *)&block, 239 (u8 *)&block); 240 /* perform KW operation: modify IV with counter */ 241 block.A ^= cpu_to_be64(t); 242 t++; 243 244 /* Copy block->R into place */ 245 scatterwalk_copychunks(&block.R, &dst_walk, SEMIBSIZE, 246 true); 247 248 nbytes -= SEMIBSIZE; 249 } 250 251 /* we now start to operate on the dst SGL only */ 252 src = req->dst; 253 dst = req->dst; 254 } 255 256 /* establish the IV for the caller to pick up */ 257 memcpy(req->iv, &block.A, SEMIBSIZE); 258 259 memzero_explicit(&block, sizeof(struct crypto_kw_block)); 260 261 return 0; 262 } 263 264 static int crypto_kw_create(struct crypto_template *tmpl, struct rtattr **tb) 265 { 266 struct skcipher_instance *inst; 267 struct crypto_alg *alg; 268 int err; 269 270 inst = skcipher_alloc_instance_simple(tmpl, tb); 271 if (IS_ERR(inst)) 272 return PTR_ERR(inst); 273 274 alg = skcipher_ialg_simple(inst); 275 276 err = -EINVAL; 277 /* Section 5.1 requirement for KW */ 278 if (alg->cra_blocksize != sizeof(struct crypto_kw_block)) 279 goto out_free_inst; 280 281 inst->alg.base.cra_blocksize = SEMIBSIZE; 282 inst->alg.base.cra_alignmask = 0; 283 inst->alg.ivsize = SEMIBSIZE; 284 285 inst->alg.encrypt = crypto_kw_encrypt; 286 inst->alg.decrypt = crypto_kw_decrypt; 287 288 err = skcipher_register_instance(tmpl, inst); 289 if (err) { 290 out_free_inst: 291 inst->free(inst); 292 } 293 294 return err; 295 } 296 297 static struct crypto_template crypto_kw_tmpl = { 298 .name = "kw", 299 .create = crypto_kw_create, 300 .module = THIS_MODULE, 301 }; 302 303 static int __init crypto_kw_init(void) 304 { 305 return crypto_register_template(&crypto_kw_tmpl); 306 } 307 308 static void __exit crypto_kw_exit(void) 309 { 310 crypto_unregister_template(&crypto_kw_tmpl); 311 } 312 313 subsys_initcall(crypto_kw_init); 314 module_exit(crypto_kw_exit); 315 316 MODULE_LICENSE("Dual BSD/GPL"); 317 MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>"); 318 MODULE_DESCRIPTION("Key Wrapping (RFC3394 / NIST SP800-38F)"); 319 MODULE_ALIAS_CRYPTO("kw"); 320 MODULE_IMPORT_NS(CRYPTO_INTERNAL); 321