1 files changed, 62 insertions, 0 deletions
diff --git a/src/lib/misc/hotp/hotp.cpp b/src/lib/misc/hotp/hotp.cpp
new file mode 100644
index 000000000..f07c11c9f
--- /dev/null
+++ b/src/lib/misc/hotp/hotp.cpp
@@ -0,0 +1,62 @@
+/*
+* HOTP
+* (C) 2017 Jack Lloyd
+*
+* Botan is released under the Simplified BSD License (see license.txt)
+*/
+
+#include <botan/hotp.h>
+
+namespace Botan {
+
+HOTP::HOTP(const SymmetricKey& key, const std::string& hash_algo, size_t digits)
+   {
+   if(digits == 6)
+      m_digit_mod = 1000000;
+   else if(digits == 7)
+      m_digit_mod = 10000000;
+   else if(digits == 8)
+      m_digit_mod = 100000000;
+   else
+      throw Invalid_Argument("Invalid HOTP digits");
+
+   /*
+   RFC 4228 only supports SHA-1 but TOTP allows SHA-256 and SHA-512
+   and some HOTP libs support one or both as extensions
+   */
+   if(hash_algo == "SHA-1")
+      m_mac = MessageAuthenticationCode::create_or_throw("HMAC(SHA-1)");
+   else if(hash_algo == "SHA-256")
+      m_mac = MessageAuthenticationCode::create_or_throw("HMAC(SHA-256)");
+   else if(hash_algo == "SHA-512")
+      m_mac = MessageAuthenticationCode::create_or_throw("HMAC(SHA-512)");
+   else
+      throw Invalid_Argument("Unsupported HOTP hash function");
+
+   m_mac->set_key(key);
+   }
+
+uint32_t HOTP::generate_hotp(uint64_t counter)
+   {
+   uint8_t counter8[8] = { 0 };
+   store_be(counter, counter8);
+   m_mac->update(counter8, sizeof(counter8));
+   const secure_vector<uint8_t> mac = m_mac->final();
+
+   const size_t offset = mac[mac.size()-1] & 0x0F;
+   const uint32_t code = load_be<uint32_t>(mac.data() + offset, 0) & 0x7FFFFFFF;
+   return code % m_digit_mod;
+   }
+
+std::pair<bool,uint64_t> HOTP::verify_hotp(uint32_t otp, uint64_t starting_counter, size_t resync_range)
+   {
+   for(size_t i = 0; i <= resync_range; ++i)
+      {
+      if(generate_hotp(starting_counter + i) == otp)
+         return std::make_pair(true, starting_counter + i + 1);
+      }
+   return std::make_pair(false, starting_counter);
+   }
+
+}
+