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