Botan  2.12.1
Crypto and TLS for C++11
hotp.cpp
Go to the documentation of this file.
1 /*
2 * HOTP
3 * (C) 2017 Jack Lloyd
4 *
5 * Botan is released under the Simplified BSD License (see license.txt)
6 */
7 
8 #include <botan/hotp.h>
9 #include <botan/loadstor.h>
10 #include <botan/exceptn.h>
11 
12 namespace Botan {
13 
14 HOTP::HOTP(const uint8_t key[], size_t key_len,
15  const std::string& hash_algo, size_t digits)
16  {
17  BOTAN_ARG_CHECK(digits == 6 || digits == 7 || digits == 8, "Invalid HOTP digits");
18 
19  if(digits == 6)
20  m_digit_mod = 1000000;
21  else if(digits == 7)
22  m_digit_mod = 10000000;
23  else if(digits == 8)
24  m_digit_mod = 100000000;
25 
26  /*
27  RFC 4228 only supports SHA-1 but TOTP allows SHA-256 and SHA-512
28  and some HOTP libs support one or both as extensions
29  */
30  if(hash_algo == "SHA-1")
31  m_mac = MessageAuthenticationCode::create_or_throw("HMAC(SHA-1)");
32  else if(hash_algo == "SHA-256")
33  m_mac = MessageAuthenticationCode::create_or_throw("HMAC(SHA-256)");
34  else if(hash_algo == "SHA-512")
35  m_mac = MessageAuthenticationCode::create_or_throw("HMAC(SHA-512)");
36  else
37  throw Invalid_Argument("Unsupported HOTP hash function");
38 
39  m_mac->set_key(key, key_len);
40  }
41 
42 uint32_t HOTP::generate_hotp(uint64_t counter)
43  {
44  m_mac->update_be(counter);
45  const secure_vector<uint8_t> mac = m_mac->final();
46 
47  const size_t offset = mac[mac.size()-1] & 0x0F;
48  const uint32_t code = load_be<uint32_t>(mac.data() + offset, 0) & 0x7FFFFFFF;
49  return code % m_digit_mod;
50  }
51 
52 std::pair<bool,uint64_t> HOTP::verify_hotp(uint32_t otp, uint64_t starting_counter, size_t resync_range)
53  {
54  for(size_t i = 0; i <= resync_range; ++i)
55  {
56  if(generate_hotp(starting_counter + i) == otp)
57  return std::make_pair(true, starting_counter + i + 1);
58  }
59  return std::make_pair(false, starting_counter);
60  }
61 
62 }
63 
uint32_t load_be< uint32_t >(const uint8_t in[], size_t off)
Definition: loadstor.h:179
Definition: alg_id.cpp:13
#define BOTAN_ARG_CHECK(expr, msg)
Definition: assert.h:37
AlgorithmIdentifier hash_algo
Definition: x509_obj.cpp:22
HOTP(const SymmetricKey &key, const std::string &hash_algo="SHA-1", size_t digits=6)
Definition: hotp.h:26
std::pair< bool, uint64_t > verify_hotp(uint32_t otp, uint64_t starting_counter, size_t resync_range=0)
Definition: hotp.cpp:52
static std::unique_ptr< MessageAuthenticationCode > create_or_throw(const std::string &algo_spec, const std::string &provider="")
Definition: mac.cpp:141
std::vector< T, secure_allocator< T > > secure_vector
Definition: secmem.h:65
uint32_t generate_hotp(uint64_t counter)
Definition: hotp.cpp:42