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
146
147
148
149
150
|
/*
* CFB Mode
* (C) 1999-2007,2013 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/cfb.h>
#include <botan/parsing.h>
#include <botan/internal/xor_buf.h>
namespace Botan {
CFB_Mode::CFB_Mode(BlockCipher* cipher, size_t feedback_bits) :
m_cipher(cipher),
m_feedback_bytes(feedback_bits ? feedback_bits / 8 : cipher->block_size())
{
if(feedback_bits % 8 || feedback() > cipher->block_size())
throw std::invalid_argument(name() + ": feedback bits " +
std::to_string(feedback_bits) + " not supported");
}
void CFB_Mode::clear()
{
m_cipher->clear();
m_shift_register.clear();
}
std::string CFB_Mode::name() const
{
if(feedback() == cipher().block_size())
return cipher().name() + "/CFB";
else
return cipher().name() + "/CFB(" + std::to_string(feedback()*8) + ")";
}
size_t CFB_Mode::output_length(size_t input_length) const
{
return input_length;
}
size_t CFB_Mode::update_granularity() const
{
return feedback();
}
size_t CFB_Mode::minimum_final_size() const
{
return 0;
}
Key_Length_Specification CFB_Mode::key_spec() const
{
return cipher().key_spec();
}
size_t CFB_Mode::default_nonce_length() const
{
return cipher().block_size();
}
bool CFB_Mode::valid_nonce_length(size_t n) const
{
return (n == cipher().block_size());
}
void CFB_Mode::key_schedule(const byte key[], size_t length)
{
m_cipher->set_key(key, length);
}
secure_vector<byte> CFB_Mode::start_raw(const byte nonce[], size_t nonce_len)
{
if(!valid_nonce_length(nonce_len))
throw Invalid_IV_Length(name(), nonce_len);
m_shift_register.assign(nonce, nonce + nonce_len);
m_keystream_buf.resize(m_shift_register.size());
cipher().encrypt(m_shift_register, m_keystream_buf);
return secure_vector<byte>();
}
void CFB_Encryption::update(secure_vector<byte>& buffer, size_t offset)
{
BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");
size_t sz = buffer.size() - offset;
byte* buf = &buffer[offset];
const size_t BS = cipher().block_size();
secure_vector<byte>& state = shift_register();
const size_t shift = feedback();
while(sz)
{
const size_t took = std::min(shift, sz);
xor_buf(&buf[0], &keystream_buf()[0], took);
// Assumes feedback-sized block except for last input
copy_mem(&state[0], &state[shift], BS - shift);
copy_mem(&state[BS-shift], &buf[0], took);
cipher().encrypt(state, keystream_buf());
buf += took;
sz -= took;
}
}
void CFB_Encryption::finish(secure_vector<byte>& buffer, size_t offset)
{
update(buffer, offset);
}
void CFB_Decryption::update(secure_vector<byte>& buffer, size_t offset)
{
BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");
size_t sz = buffer.size() - offset;
byte* buf = &buffer[offset];
const size_t BS = cipher().block_size();
secure_vector<byte>& state = shift_register();
const size_t shift = feedback();
while(sz)
{
const size_t took = std::min(shift, sz);
// first update shift register with ciphertext
copy_mem(&state[0], &state[shift], BS - shift);
copy_mem(&state[BS-shift], &buf[0], took);
// then decrypt
xor_buf(&buf[0], &keystream_buf()[0], took);
// then update keystream
cipher().encrypt(state, keystream_buf());
buf += took;
sz -= took;
}
}
void CFB_Decryption::finish(secure_vector<byte>& buffer, size_t offset)
{
update(buffer, offset);
}
}
|
