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
|
/*
* Counter mode
* (C) 1999-2011 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/ctr.h>
#include <botan/internal/xor_buf.h>
namespace Botan {
/*
* CTR-BE Constructor
*/
CTR_BE::CTR_BE(BlockCipher* ciph) :
permutation(ciph),
counter(256 * permutation->block_size()),
buffer(counter.size()),
position(0)
{
}
/*
* CTR_BE Destructor
*/
CTR_BE::~CTR_BE()
{
delete permutation;
}
/*
* Zeroize
*/
void CTR_BE::clear()
{
permutation->clear();
zeroise(buffer);
zeroise(counter);
position = 0;
}
/*
* Set the key
*/
void CTR_BE::key_schedule(const byte key[], size_t key_len)
{
permutation->set_key(key, key_len);
// Set a default all-zeros IV
set_iv(0, 0);
}
/*
* Return the name of this type
*/
std::string CTR_BE::name() const
{
return ("CTR-BE(" + permutation->name() + ")");
}
/*
* CTR-BE Encryption/Decryption
*/
void CTR_BE::cipher(const byte in[], byte out[], size_t length)
{
while(length >= buffer.size() - position)
{
xor_buf(out, in, &buffer[position], buffer.size() - position);
length -= (buffer.size() - position);
in += (buffer.size() - position);
out += (buffer.size() - position);
increment_counter();
}
xor_buf(out, in, &buffer[position], length);
position += length;
}
/*
* Set CTR-BE IV
*/
void CTR_BE::set_iv(const byte iv[], size_t iv_len)
{
if(!valid_iv_length(iv_len))
throw Invalid_IV_Length(name(), iv_len);
const size_t bs = permutation->block_size();
zeroise(counter);
buffer_insert(counter, 0, iv, iv_len);
/*
* Set counter blocks to IV, IV + 1, ... IV + 255
*/
for(size_t i = 1; i != 256; ++i)
{
buffer_insert(counter, i*bs, &counter[(i-1)*bs], bs);
for(size_t j = 0; j != bs; ++j)
if(++counter[i*bs + (bs - 1 - j)])
break;
}
permutation->encrypt_n(&counter[0], &buffer[0], 256);
position = 0;
}
/*
* Increment the counter and update the buffer
*/
void CTR_BE::increment_counter()
{
const size_t bs = permutation->block_size();
/*
* Each counter value always needs to be incremented by 256,
* so we don't touch the lowest byte and instead treat it as
* an increment of one starting with the next byte.
*/
for(size_t i = 0; i != 256; ++i)
{
for(size_t j = 1; j != bs; ++j)
if(++counter[i*bs + (bs - 1 - j)])
break;
}
permutation->encrypt_n(&counter[0], &buffer[0], 256);
position = 0;
}
}
|
