2 * Key Wrapping: RFC3394 / NIST SP800-38F
4 * Copyright (C) 2015, Stephan Mueller <smueller@chronox.de>
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19 * ALTERNATIVELY, this product may be distributed under the terms of
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22 * necessary due to a potential bad interaction between the GPL and
23 * the restrictions contained in a BSD-style copyright.)
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40 * Note for using key wrapping:
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.
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.
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:
54 * unsigned int datalen = ptlen + crypto_skcipher_ivsize(tfm);
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);
62 * ==> After encryption, data now contains full KW result as per SP800-38F.
64 * In case of decryption, ciphertext now already has the expected length
65 * and must be segmented appropriately:
67 * unsigned int datalen = CTLEN;
69 * <ensure that data contains full ciphertext>
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);
76 * ==> After decryption (which hopefully does not return EBADMSG), the ct
77 * pointer now points to the plaintext of size ctlen.
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.
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>
90 struct crypto_kw_block {
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
101 static void crypto_kw_scatterlist_ff(struct scatter_walk *walk,
102 struct scatterlist *sg,
105 unsigned int skip = 0;
107 /* The caller should only operate on full SEMIBLOCKs. */
108 BUG_ON(end < SEMIBSIZE);
110 skip = end - SEMIBSIZE;
112 if (sg->length > skip) {
113 scatterwalk_start(walk, sg);
114 scatterwalk_advance(walk, skip);
123 static int crypto_kw_decrypt(struct skcipher_request *req)
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);
134 * Require at least 2 semiblocks (note, the 3rd semiblock that is
135 * required by SP800-38F is the IV.
137 if (req->cryptlen < (2 * SEMIBSIZE) || req->cryptlen % SEMIBSIZE)
140 /* Place the IV into block A */
141 memcpy(&block.A, req->iv, SEMIBSIZE);
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.
151 for (i = 0; i < 6; i++) {
152 struct scatter_walk src_walk, dst_walk;
153 unsigned int nbytes = req->cryptlen;
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,
162 /* perform KW operation: modify IV with counter */
163 block.A ^= cpu_to_be64(t);
165 /* perform KW operation: decrypt block */
166 crypto_cipher_decrypt_one(cipher, (u8 *)&block,
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,
178 /* we now start to operate on the dst SGL only */
183 /* Perform authentication check */
184 if (block.A != cpu_to_be64(0xa6a6a6a6a6a6a6a6ULL))
187 memzero_explicit(&block, sizeof(struct crypto_kw_block));
192 static int crypto_kw_encrypt(struct skcipher_request *req)
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;
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.
207 if (req->cryptlen < (2 * SEMIBSIZE) || req->cryptlen % SEMIBSIZE)
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.
214 block.A = cpu_to_be64(0xa6a6a6a6a6a6a6a6ULL);
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.
224 for (i = 0; i < 6; i++) {
225 struct scatter_walk src_walk, dst_walk;
226 unsigned int nbytes = req->cryptlen;
228 scatterwalk_start(&src_walk, src);
229 scatterwalk_start(&dst_walk, dst);
232 /* get the source block */
233 scatterwalk_copychunks(&block.R, &src_walk, SEMIBSIZE,
236 /* perform KW operation: encrypt block */
237 crypto_cipher_encrypt_one(cipher, (u8 *)&block,
239 /* perform KW operation: modify IV with counter */
240 block.A ^= cpu_to_be64(t);
243 /* Copy block->R into place */
244 scatterwalk_copychunks(&block.R, &dst_walk, SEMIBSIZE,
250 /* we now start to operate on the dst SGL only */
255 /* establish the IV for the caller to pick up */
256 memcpy(req->iv, &block.A, SEMIBSIZE);
258 memzero_explicit(&block, sizeof(struct crypto_kw_block));
263 static int crypto_kw_create(struct crypto_template *tmpl, struct rtattr **tb)
265 struct skcipher_instance *inst;
266 struct crypto_alg *alg;
269 inst = skcipher_alloc_instance_simple(tmpl, tb);
271 return PTR_ERR(inst);
273 alg = skcipher_ialg_simple(inst);
276 /* Section 5.1 requirement for KW */
277 if (alg->cra_blocksize != sizeof(struct crypto_kw_block))
280 inst->alg.base.cra_blocksize = SEMIBSIZE;
281 inst->alg.base.cra_alignmask = 0;
282 inst->alg.ivsize = SEMIBSIZE;
284 inst->alg.encrypt = crypto_kw_encrypt;
285 inst->alg.decrypt = crypto_kw_decrypt;
287 err = skcipher_register_instance(tmpl, inst);
296 static struct crypto_template crypto_kw_tmpl = {
298 .create = crypto_kw_create,
299 .module = THIS_MODULE,
302 static int __init crypto_kw_init(void)
304 return crypto_register_template(&crypto_kw_tmpl);
307 static void __exit crypto_kw_exit(void)
309 crypto_unregister_template(&crypto_kw_tmpl);
312 subsys_initcall(crypto_kw_init);
313 module_exit(crypto_kw_exit);
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");