1 /*
2 * Copyright (c) 2018 Thomas Pornin <pornin@bolet.org>
3 *
4 * Permission is hereby granted, free of charge, to any person obtaining
5 * a copy of this software and associated documentation files (the
6 * "Software"), to deal in the Software without restriction, including
7 * without limitation the rights to use, copy, modify, merge, publish,
8 * distribute, sublicense, and/or sell copies of the Software, and to
9 * permit persons to whom the Software is furnished to do so, subject to
10 * the following conditions:
11 *
12 * The above copyright notice and this permission notice shall be
13 * included in all copies or substantial portions of the Software.
14 *
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
16 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
17 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
18 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
19 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
20 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
21 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
22 * SOFTWARE.
23 */
24
25 #include "inner.h"
26
27 /*
28 * Hash some data. This is put as a separate function so that stack
29 * allocation of the hash function context is done only for the duration
30 * of the hash.
31 */
32 static void
hash_data(const br_hash_class * dig,void * dst,const void * src,size_t len)33 hash_data(const br_hash_class *dig, void *dst, const void *src, size_t len)
34 {
35 br_hash_compat_context hc;
36
37 hc.vtable = dig;
38 dig->init(&hc.vtable);
39 dig->update(&hc.vtable, src, len);
40 dig->out(&hc.vtable, dst);
41 }
42
43 /* see inner.h */
44 size_t
br_rsa_oaep_pad(const br_prng_class ** rnd,const br_hash_class * dig,const void * label,size_t label_len,const br_rsa_public_key * pk,void * dst,size_t dst_max_len,const void * src,size_t src_len)45 br_rsa_oaep_pad(const br_prng_class **rnd, const br_hash_class *dig,
46 const void *label, size_t label_len,
47 const br_rsa_public_key *pk,
48 void *dst, size_t dst_max_len,
49 const void *src, size_t src_len)
50 {
51 size_t k, hlen;
52 unsigned char *buf;
53
54 hlen = br_digest_size(dig);
55
56 /*
57 * Compute actual modulus length (in bytes).
58 */
59 k = pk->nlen;
60 while (k > 0 && pk->n[k - 1] == 0) {
61 k --;
62 }
63
64 /*
65 * An error is reported if:
66 * - the modulus is too short;
67 * - the source message length is too long;
68 * - the destination buffer is too short.
69 */
70 if (k < ((hlen << 1) + 2)
71 || src_len > (k - (hlen << 1) - 2)
72 || dst_max_len < k)
73 {
74 return 0;
75 }
76
77 /*
78 * Apply padding. At this point, things cannot fail.
79 */
80 buf = dst;
81
82 /*
83 * Assemble: DB = lHash || PS || 0x01 || M
84 * We first place the source message M with memmove(), so that
85 * overlaps between source and destination buffers are supported.
86 */
87 memmove(buf + k - src_len, src, src_len);
88 hash_data(dig, buf + 1 + hlen, label, label_len);
89 memset(buf + 1 + (hlen << 1), 0, k - src_len - (hlen << 1) - 2);
90 buf[k - src_len - 1] = 0x01;
91
92 /*
93 * Make the random seed.
94 */
95 (*rnd)->generate(rnd, buf + 1, hlen);
96
97 /*
98 * Mask DB with the mask generated from the seed.
99 */
100 br_mgf1_xor(buf + 1 + hlen, k - hlen - 1, dig, buf + 1, hlen);
101
102 /*
103 * Mask the seed with the mask generated from the masked DB.
104 */
105 br_mgf1_xor(buf + 1, hlen, dig, buf + 1 + hlen, k - hlen - 1);
106
107 /*
108 * Padding result: EM = 0x00 || maskedSeed || maskedDB.
109 */
110 buf[0] = 0x00;
111 return k;
112 }
113