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
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
|
/*
* CFB Mode
* (C) 1999-2007,2013,2017 Jack Lloyd
* (C) 2016 Daniel Neus, Rohde & Schwarz Cybersecurity
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/cfb.h>
namespace Botan {
CFB_Mode::CFB_Mode(BlockCipher* cipher, size_t feedback_bits) :
m_cipher(cipher),
m_block_size(m_cipher->block_size()),
m_feedback_bytes(feedback_bits ? feedback_bits / 8 : m_block_size)
{
if(feedback_bits % 8 || feedback() > cipher->block_size())
throw Invalid_Argument(name() + ": feedback bits " +
std::to_string(feedback_bits) + " not supported");
}
void CFB_Mode::clear()
{
m_cipher->clear();
m_keystream.clear();
reset();
}
void CFB_Mode::reset()
{
m_state.clear();
zeroise(m_keystream);
}
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 block_size();
}
bool CFB_Mode::valid_nonce_length(size_t n) const
{
return (n == 0 || n == block_size());
}
void CFB_Mode::key_schedule(const uint8_t key[], size_t length)
{
m_cipher->set_key(key, length);
m_keystream.resize(m_cipher->block_size());
}
void CFB_Mode::start_msg(const uint8_t nonce[], size_t nonce_len)
{
if(!valid_nonce_length(nonce_len))
throw Invalid_IV_Length(name(), nonce_len);
verify_key_set(!m_keystream.empty());
if(nonce_len == 0)
{
if(m_state.empty())
{
throw Invalid_State("CFB requires a non-empty initial nonce");
}
// No reason to encrypt state->keystream_buf, because no change
}
else
{
m_state.assign(nonce, nonce + nonce_len);
cipher().encrypt(m_state, m_keystream);
m_keystream_pos = 0;
}
}
void CFB_Mode::shift_register()
{
const size_t shift = feedback();
const size_t carryover = block_size() - shift;
if(carryover > 0)
{
copy_mem(m_state.data(), &m_state[shift], carryover);
}
copy_mem(&m_state[carryover], m_keystream.data(), shift);
cipher().encrypt(m_state, m_keystream);
m_keystream_pos = 0;
}
size_t CFB_Encryption::process(uint8_t buf[], size_t sz)
{
verify_key_set(!m_keystream.empty());
BOTAN_STATE_CHECK(m_state.empty() == false);
const size_t shift = feedback();
size_t left = sz;
if(m_keystream_pos != 0)
{
const size_t take = std::min<size_t>(left, shift - m_keystream_pos);
xor_buf(m_keystream.data() + m_keystream_pos, buf, take);
copy_mem(buf, m_keystream.data() + m_keystream_pos, take);
m_keystream_pos += take;
left -= take;
buf += take;
if(m_keystream_pos == shift)
{
shift_register();
}
}
while(left >= shift)
{
xor_buf(m_keystream.data(), buf, shift);
copy_mem(buf, m_keystream.data(), shift);
left -= shift;
buf += shift;
shift_register();
}
if(left > 0)
{
xor_buf(m_keystream.data(), buf, left);
copy_mem(buf, m_keystream.data(), left);
m_keystream_pos += left;
}
return sz;
}
void CFB_Encryption::finish(secure_vector<uint8_t>& buffer, size_t offset)
{
update(buffer, offset);
}
namespace {
inline void xor_copy(uint8_t buf[], uint8_t key_buf[], size_t len)
{
for(size_t i = 0; i != len; ++i)
{
uint8_t k = key_buf[i];
key_buf[i] = buf[i];
buf[i] ^= k;
}
}
}
size_t CFB_Decryption::process(uint8_t buf[], size_t sz)
{
verify_key_set(!m_keystream.empty());
BOTAN_STATE_CHECK(m_state.empty() == false);
const size_t shift = feedback();
size_t left = sz;
if(m_keystream_pos != 0)
{
const size_t take = std::min<size_t>(left, shift - m_keystream_pos);
xor_copy(buf, m_keystream.data() + m_keystream_pos, take);
m_keystream_pos += take;
left -= take;
buf += take;
if(m_keystream_pos == shift)
{
shift_register();
}
}
while(left >= shift)
{
xor_copy(buf, m_keystream.data(), shift);
left -= shift;
buf += shift;
shift_register();
}
if(left > 0)
{
xor_copy(buf, m_keystream.data(), left);
m_keystream_pos += left;
}
return sz;
}
void CFB_Decryption::finish(secure_vector<uint8_t>& buffer, size_t offset)
{
update(buffer, offset);
}
}
|
