Botan  2.1.0
Crypto and TLS for C++11
rc4.cpp
Go to the documentation of this file.
1 /*
2 * RC4
3 * (C) 1999-2007 Jack Lloyd
4 *
5 * Botan is released under the Simplified BSD License (see license.txt)
6 */
7 
8 #include <botan/rc4.h>
9 #include <botan/exceptn.h>
10 
11 namespace Botan {
12 
13 /*
14 * Combine cipher stream with message
15 */
16 void RC4::cipher(const uint8_t in[], uint8_t out[], size_t length)
17  {
18  while(length >= m_buffer.size() - m_position)
19  {
20  xor_buf(out, in, &m_buffer[m_position], m_buffer.size() - m_position);
21  length -= (m_buffer.size() - m_position);
22  in += (m_buffer.size() - m_position);
23  out += (m_buffer.size() - m_position);
24  generate();
25  }
26  xor_buf(out, in, &m_buffer[m_position], length);
27  m_position += length;
28  }
29 
30 void RC4::set_iv(const uint8_t*, size_t length)
31  {
32  if(length > 0)
33  throw Exception("RC4 does not support an IV");
34  }
35 
36 /*
37 * Generate cipher stream
38 */
39 void RC4::generate()
40  {
41  uint8_t SX, SY;
42  for(size_t i = 0; i != m_buffer.size(); i += 4)
43  {
44  SX = m_state[m_X+1]; m_Y = (m_Y + SX) % 256; SY = m_state[m_Y];
45  m_state[m_X+1] = SY; m_state[m_Y] = SX;
46  m_buffer[i] = m_state[(SX + SY) % 256];
47 
48  SX = m_state[m_X+2]; m_Y = (m_Y + SX) % 256; SY = m_state[m_Y];
49  m_state[m_X+2] = SY; m_state[m_Y] = SX;
50  m_buffer[i+1] = m_state[(SX + SY) % 256];
51 
52  SX = m_state[m_X+3]; m_Y = (m_Y + SX) % 256; SY = m_state[m_Y];
53  m_state[m_X+3] = SY; m_state[m_Y] = SX;
54  m_buffer[i+2] = m_state[(SX + SY) % 256];
55 
56  m_X = (m_X + 4) % 256;
57  SX = m_state[m_X]; m_Y = (m_Y + SX) % 256; SY = m_state[m_Y];
58  m_state[m_X] = SY; m_state[m_Y] = SX;
59  m_buffer[i+3] = m_state[(SX + SY) % 256];
60  }
61  m_position = 0;
62  }
63 
64 /*
65 * RC4 Key Schedule
66 */
67 void RC4::key_schedule(const uint8_t key[], size_t length)
68  {
69  m_state.resize(256);
70  m_buffer.resize(256);
71 
72  m_position = m_X = m_Y = 0;
73 
74  for(size_t i = 0; i != 256; ++i)
75  m_state[i] = static_cast<uint8_t>(i);
76 
77  for(size_t i = 0, state_index = 0; i != 256; ++i)
78  {
79  state_index = (state_index + key[i % length] + m_state[i]) % 256;
80  std::swap(m_state[i], m_state[state_index]);
81  }
82 
83  for(size_t i = 0; i <= m_SKIP; i += m_buffer.size())
84  generate();
85 
86  m_position += (m_SKIP % m_buffer.size());
87  }
88 
89 /*
90 * Return the name of this type
91 */
92 std::string RC4::name() const
93  {
94  if(m_SKIP == 0) return "RC4";
95  if(m_SKIP == 256) return "MARK-4";
96  else return "RC4_skip(" + std::to_string(m_SKIP) + ")";
97  }
98 
99 /*
100 * Clear memory of sensitive data
101 */
103  {
104  zap(m_state);
105  zap(m_buffer);
106  m_position = m_X = m_Y = 0;
107  }
108 
109 /*
110 * RC4 Constructor
111 */
112 RC4::RC4(size_t s) : m_SKIP(s) {}
113 
114 void RC4::seek(uint64_t)
115  {
116  throw Exception("RC4 does not support seeking");
117  }
118 }
void xor_buf(T out[], const T in[], size_t length)
Definition: mem_ops.h:115
void clear() override
Definition: rc4.cpp:102
void zap(std::vector< T, Alloc > &vec)
Definition: secmem.h:221
std::string to_string(const BER_Object &obj)
Definition: asn1_obj.cpp:47
void seek(uint64_t offset) override
Definition: rc4.cpp:114
void cipher(const uint8_t in[], uint8_t out[], size_t length) override
Definition: rc4.cpp:16
Definition: alg_id.cpp:13
std::string name() const override
Definition: rc4.cpp:92
void set_iv(const uint8_t iv[], size_t iv_len) override
Definition: rc4.cpp:30
RC4(size_t skip=0)
Definition: rc4.cpp:112