Botan  2.7.0
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 
62 std::string EAX_Mode::name() const
63  {
64  return (m_cipher->name() + "/EAX");
65  }
66 
68  {
69  /*
70  * For EAX this actually can be as low as 1 but that causes problems
71  * for applications which use update_granularity as the buffer size.
72  */
73  return m_cipher->parallel_bytes();
74  }
75 
77  {
78  return m_cipher->key_spec();
79  }
80 
81 /*
82 * Set the EAX key
83 */
84 void EAX_Mode::key_schedule(const uint8_t key[], size_t length)
85  {
86  /*
87  * These could share the key schedule, which is one nice part of EAX,
88  * but it's much easier to ignore that here...
89  */
90  m_ctr->set_key(key, length);
91  m_cmac->set_key(key, length);
92  }
93 
94 /*
95 * Set the EAX associated data
96 */
97 void EAX_Mode::set_associated_data(const uint8_t ad[], size_t length)
98  {
99  m_ad_mac = eax_prf(1, block_size(), *m_cmac, ad, length);
100  }
101 
102 void EAX_Mode::start_msg(const uint8_t nonce[], size_t nonce_len)
103  {
104  if(!valid_nonce_length(nonce_len))
105  throw Invalid_IV_Length(name(), nonce_len);
106 
107  m_nonce_mac = eax_prf(0, block_size(), *m_cmac, nonce, nonce_len);
108 
109  m_ctr->set_iv(m_nonce_mac.data(), m_nonce_mac.size());
110 
111  for(size_t i = 0; i != block_size() - 1; ++i)
112  m_cmac->update(0);
113  m_cmac->update(2);
114  }
115 
116 size_t EAX_Encryption::process(uint8_t buf[], size_t sz)
117  {
118  m_ctr->cipher(buf, buf, sz);
119  m_cmac->update(buf, sz);
120  return sz;
121  }
122 
123 void EAX_Encryption::finish(secure_vector<uint8_t>& buffer, size_t offset)
124  {
125  update(buffer, offset);
126 
127  secure_vector<uint8_t> data_mac = m_cmac->final();
128  xor_buf(data_mac, m_nonce_mac, data_mac.size());
129 
130  if(m_ad_mac.empty())
131  {
132  m_ad_mac = eax_prf(1, block_size(), *m_cmac, nullptr, 0);
133  }
134 
135  xor_buf(data_mac, m_ad_mac, data_mac.size());
136 
137  buffer += std::make_pair(data_mac.data(), tag_size());
138  }
139 
140 size_t EAX_Decryption::process(uint8_t buf[], size_t sz)
141  {
142  m_cmac->update(buf, sz);
143  m_ctr->cipher(buf, buf, sz);
144  return sz;
145  }
146 
147 void EAX_Decryption::finish(secure_vector<uint8_t>& buffer, size_t offset)
148  {
149  BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");
150  const size_t sz = buffer.size() - offset;
151  uint8_t* buf = buffer.data() + offset;
152 
153  BOTAN_ASSERT(sz >= tag_size(), "Have the tag as part of final input");
154 
155  const size_t remaining = sz - tag_size();
156 
157  if(remaining)
158  {
159  m_cmac->update(buf, remaining);
160  m_ctr->cipher(buf, buf, remaining);
161  }
162 
163  const uint8_t* included_tag = &buf[remaining];
164 
165  secure_vector<uint8_t> mac = m_cmac->final();
166  mac ^= m_nonce_mac;
167 
168  if(m_ad_mac.empty())
169  {
170  m_ad_mac = eax_prf(1, block_size(), *m_cmac, nullptr, 0);
171  }
172 
173  mac ^= m_ad_mac;
174 
175  if(!constant_time_compare(mac.data(), included_tag, tag_size()))
176  throw Integrity_Failure("EAX tag check failed");
177 
178  buffer.resize(offset + remaining);
179  }
180 
181 }
void finish(secure_vector< uint8_t > &final_block, size_t offset=0) override
Definition: eax.cpp:147
Key_Length_Specification key_spec() const override
Definition: eax.cpp:76
size_t process(uint8_t buf[], size_t size) override
Definition: eax.cpp:116
std::string name() const override
Definition: eax.cpp:62
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:115
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
std::string to_string(const BER_Object &obj)
Definition: asn1_obj.cpp:210
#define BOTAN_ASSERT(expr, assertion_made)
Definition: assert.h:43
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:140
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:67
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:97
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:123