1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
|
/*
* EMSA4
* (C) 1999-2007 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/emsa4.h>
#include <botan/mgf1.h>
#include <botan/internal/bit_ops.h>
namespace Botan {
/*
* EMSA4 Update Operation
*/
void EMSA4::update(const byte input[], size_t length)
{
hash->update(input, length);
}
/*
* Return the raw (unencoded) data
*/
SecureVector<byte> EMSA4::raw_data()
{
return hash->final();
}
/*
* EMSA4 Encode Operation
*/
SecureVector<byte> EMSA4::encoding_of(const MemoryRegion<byte>& msg,
size_t output_bits,
RandomNumberGenerator& rng)
{
const size_t HASH_SIZE = hash->output_length();
if(msg.size() != HASH_SIZE)
throw Encoding_Error("EMSA4::encoding_of: Bad input length");
if(output_bits < 8*HASH_SIZE + 8*SALT_SIZE + 9)
throw Encoding_Error("EMSA4::encoding_of: Output length is too small");
const size_t output_length = (output_bits + 7) / 8;
SecureVector<byte> salt = rng.random_vec(SALT_SIZE);
for(size_t j = 0; j != 8; ++j)
hash->update(0);
hash->update(msg);
hash->update(salt, SALT_SIZE);
SecureVector<byte> H = hash->final();
SecureVector<byte> EM(output_length);
EM[output_length - HASH_SIZE - SALT_SIZE - 2] = 0x01;
buffer_insert(EM, output_length - 1 - HASH_SIZE - SALT_SIZE, salt);
mgf->mask(H, HASH_SIZE, EM, output_length - HASH_SIZE - 1);
EM[0] &= 0xFF >> (8 * ((output_bits + 7) / 8) - output_bits);
buffer_insert(EM, output_length - 1 - HASH_SIZE, H);
EM[output_length-1] = 0xBC;
return EM;
}
/*
* EMSA4 Decode/Verify Operation
*/
bool EMSA4::verify(const MemoryRegion<byte>& const_coded,
const MemoryRegion<byte>& raw, size_t key_bits)
{
const size_t HASH_SIZE = hash->output_length();
const size_t KEY_BYTES = (key_bits + 7) / 8;
if(key_bits < 8*HASH_SIZE + 9)
return false;
if(raw.size() != HASH_SIZE)
return false;
if(const_coded.size() > KEY_BYTES || const_coded.size() <= 1)
return false;
if(const_coded[const_coded.size()-1] != 0xBC)
return false;
SecureVector<byte> coded = const_coded;
if(coded.size() < KEY_BYTES)
{
SecureVector<byte> temp(KEY_BYTES);
buffer_insert(temp, KEY_BYTES - coded.size(), coded);
coded = temp;
}
const size_t TOP_BITS = 8 * ((key_bits + 7) / 8) - key_bits;
if(TOP_BITS > 8 - high_bit(coded[0]))
return false;
SecureVector<byte> DB(&coded[0], coded.size() - HASH_SIZE - 1);
SecureVector<byte> H(&coded[coded.size() - HASH_SIZE - 1], HASH_SIZE);
mgf->mask(H, H.size(), DB, coded.size() - H.size() - 1);
DB[0] &= 0xFF >> TOP_BITS;
size_t salt_offset = 0;
for(size_t j = 0; j != DB.size(); ++j)
{
if(DB[j] == 0x01)
{ salt_offset = j + 1; break; }
if(DB[j])
return false;
}
if(salt_offset == 0)
return false;
SecureVector<byte> salt(&DB[salt_offset], DB.size() - salt_offset);
for(size_t j = 0; j != 8; ++j)
hash->update(0);
hash->update(raw);
hash->update(salt);
SecureVector<byte> H2 = hash->final();
return (H == H2);
}
/*
* EMSA4 Constructor
*/
EMSA4::EMSA4(HashFunction* h) :
SALT_SIZE(h->output_length()), hash(h)
{
mgf = new MGF1(hash->clone());
}
/*
* EMSA4 Constructor
*/
EMSA4::EMSA4(HashFunction* h, size_t salt_size) :
SALT_SIZE(salt_size), hash(h)
{
mgf = new MGF1(hash->clone());
}
}
|
