Botan  2.8.0
Crypto and TLS for C++11
eax.cpp
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1 /*
2 * EAX Mode Encryption
3 * (C) 1999-2007 Jack Lloyd
4 * (C) 2016 Daniel Neus, Rohde & Schwarz Cybersecurity
5 *
6 * Botan is released under the Simplified BSD License (see license.txt)
7 */
8 
9 #include <botan/eax.h>
10 #include <botan/cmac.h>
11 #include <botan/ctr.h>
12 
13 namespace Botan {
14 
15 namespace {
16 
17 /*
18 * EAX MAC-based PRF
19 */
20 secure_vector<uint8_t> eax_prf(uint8_t tag, size_t block_size,
21  MessageAuthenticationCode& mac,
22  const uint8_t in[], size_t length)
23  {
24  for(size_t i = 0; i != block_size - 1; ++i)
25  {
26  mac.update(0);
27  }
28  mac.update(tag);
29  mac.update(in, length);
30  return mac.final();
31  }
32 
33 }
34 
35 /*
36 * EAX_Mode Constructor
37 */
38 EAX_Mode::EAX_Mode(BlockCipher* cipher, size_t tag_size) :
39  m_tag_size(tag_size ? tag_size : cipher->block_size()),
40  m_cipher(cipher),
41  m_ctr(new CTR_BE(m_cipher->clone())),
42  m_cmac(new CMAC(m_cipher->clone()))
43  {
44  if(m_tag_size < 8 || m_tag_size > m_cmac->output_length())
45  throw Invalid_Argument(name() + ": Bad tag size " + std::to_string(tag_size));
46  }
47 
49  {
50  m_cipher->clear();
51  m_ctr->clear();
52  m_cmac->clear();
53  reset();
54  }
55 
57  {
58  m_ad_mac.clear();
59  m_nonce_mac.clear();
60 
61  // Clear out any data added to the CMAC calculation
62  try {
63  m_cmac->final();
64  }
65  catch(Key_Not_Set&) {}
66  }
67 
68 std::string EAX_Mode::name() const
69  {
70  return (m_cipher->name() + "/EAX");
71  }
72 
74  {
75  /*
76  * For EAX this actually can be as low as 1 but that causes problems
77  * for applications which use update_granularity as the buffer size.
78  */
79  return m_cipher->parallel_bytes();
80  }
81 
83  {
84  return m_cipher->key_spec();
85  }
86 
87 /*
88 * Set the EAX key
89 */
90 void EAX_Mode::key_schedule(const uint8_t key[], size_t length)
91  {
92  /*
93  * These could share the key schedule, which is one nice part of EAX,
94  * but it's much easier to ignore that here...
95  */
96  m_ctr->set_key(key, length);
97  m_cmac->set_key(key, length);
98  }
99 
100 /*
101 * Set the EAX associated data
102 */
103 void EAX_Mode::set_associated_data(const uint8_t ad[], size_t length)
104  {
105  m_ad_mac = eax_prf(1, block_size(), *m_cmac, ad, length);
106  }
107 
108 void EAX_Mode::start_msg(const uint8_t nonce[], size_t nonce_len)
109  {
110  if(!valid_nonce_length(nonce_len))
111  throw Invalid_IV_Length(name(), nonce_len);
112 
113  m_nonce_mac = eax_prf(0, block_size(), *m_cmac, nonce, nonce_len);
114 
115  m_ctr->set_iv(m_nonce_mac.data(), m_nonce_mac.size());
116 
117  for(size_t i = 0; i != block_size() - 1; ++i)
118  m_cmac->update(0);
119  m_cmac->update(2);
120  }
121 
122 size_t EAX_Encryption::process(uint8_t buf[], size_t sz)
123  {
124  BOTAN_STATE_CHECK(m_nonce_mac.size() > 0);
125  m_ctr->cipher(buf, buf, sz);
126  m_cmac->update(buf, sz);
127  return sz;
128  }
129 
130 void EAX_Encryption::finish(secure_vector<uint8_t>& buffer, size_t offset)
131  {
132  BOTAN_ASSERT_NOMSG(m_nonce_mac.empty() == false);
133  update(buffer, offset);
134 
135  secure_vector<uint8_t> data_mac = m_cmac->final();
136  xor_buf(data_mac, m_nonce_mac, data_mac.size());
137 
138  if(m_ad_mac.empty())
139  {
140  m_ad_mac = eax_prf(1, block_size(), *m_cmac, nullptr, 0);
141  }
142 
143  xor_buf(data_mac, m_ad_mac, data_mac.size());
144 
145  buffer += std::make_pair(data_mac.data(), tag_size());
146  }
147 
148 size_t EAX_Decryption::process(uint8_t buf[], size_t sz)
149  {
150  BOTAN_STATE_CHECK(m_nonce_mac.size() > 0);
151  m_cmac->update(buf, sz);
152  m_ctr->cipher(buf, buf, sz);
153  return sz;
154  }
155 
156 void EAX_Decryption::finish(secure_vector<uint8_t>& buffer, size_t offset)
157  {
158  BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");
159  const size_t sz = buffer.size() - offset;
160  uint8_t* buf = buffer.data() + offset;
161 
162  BOTAN_ASSERT(sz >= tag_size(), "Have the tag as part of final input");
163 
164  const size_t remaining = sz - tag_size();
165 
166  if(remaining)
167  {
168  m_cmac->update(buf, remaining);
169  m_ctr->cipher(buf, buf, remaining);
170  }
171 
172  const uint8_t* included_tag = &buf[remaining];
173 
174  secure_vector<uint8_t> mac = m_cmac->final();
175  mac ^= m_nonce_mac;
176 
177  if(m_ad_mac.empty())
178  {
179  m_ad_mac = eax_prf(1, block_size(), *m_cmac, nullptr, 0);
180  }
181 
182  mac ^= m_ad_mac;
183 
184  if(!constant_time_compare(mac.data(), included_tag, tag_size()))
185  throw Integrity_Failure("EAX tag check failed");
186 
187  buffer.resize(offset + remaining);
188 
189  m_nonce_mac.clear();
190  }
191 
192 }
void finish(secure_vector< uint8_t > &final_block, size_t offset=0) override
Definition: eax.cpp:156
Key_Length_Specification key_spec() const override
Definition: eax.cpp:82
size_t process(uint8_t buf[], size_t size) override
Definition: eax.cpp:122
std::string name() const override
Definition: eax.cpp:68
void clear() override
Definition: eax.cpp:48
size_t block_size() const
Definition: eax.h:49
void update(secure_vector< uint8_t > &buffer, size_t offset=0)
Definition: cipher_mode.h:112
secure_vector< uint8_t > m_ad_mac
Definition: eax.h:57
secure_vector< uint8_t > m_nonce_mac
Definition: eax.h:59
bool constant_time_compare(const uint8_t x[], const uint8_t y[], size_t len)
Definition: mem_ops.cpp:51
#define BOTAN_STATE_CHECK(expr)
Definition: assert.h:49
#define BOTAN_ASSERT_NOMSG(expr)
Definition: assert.h:68
std::string to_string(const BER_Object &obj)
Definition: asn1_obj.cpp:210
#define BOTAN_ASSERT(expr, assertion_made)
Definition: assert.h:55
void xor_buf(uint8_t out[], const uint8_t in[], size_t length)
Definition: mem_ops.h:174
bool valid_nonce_length(size_t) const override
Definition: eax.h:34
EAX_Mode(BlockCipher *cipher, size_t tag_size)
Definition: eax.cpp:38
size_t process(uint8_t buf[], size_t size) override
Definition: eax.cpp:148
Definition: alg_id.cpp:13
std::unique_ptr< BlockCipher > m_cipher
Definition: eax.h:53
size_t tag_size() const override
Definition: eax.h:36
void reset() override
Definition: eax.cpp:56
std::unique_ptr< MessageAuthenticationCode > m_cmac
Definition: eax.h:55
size_t update_granularity() const override
Definition: eax.cpp:73
std::vector< T, secure_allocator< T > > secure_vector
Definition: secmem.h:88
void set_associated_data(const uint8_t ad[], size_t ad_len) override
Definition: eax.cpp:103
std::unique_ptr< StreamCipher > m_ctr
Definition: eax.h:54
void finish(secure_vector< uint8_t > &final_block, size_t offset=0) override
Definition: eax.cpp:130