1 files changed, 63 insertions, 0 deletions
diff --git a/src/lib/misc/hotp/totp.cpp b/src/lib/misc/hotp/totp.cpp
new file mode 100644
index 000000000..c3203c32a
--- /dev/null
+++ b/src/lib/misc/hotp/totp.cpp
@@ -0,0 +1,63 @@
+/*
+* TOTP
+* (C) 2017 Jack Lloyd
+*
+* Botan is released under the Simplified BSD License (see license.txt)
+*/
+
+#include <botan/totp.h>
+#include <botan/calendar.h>
+
+namespace Botan {
+
+TOTP::TOTP(const SymmetricKey& key, const std::string& hash_algo,
+           size_t digits, size_t time_step)
+   : m_hotp(key, hash_algo, digits)
+   , m_time_step(time_step)
+   , m_unix_epoch(calendar_point(1970, 1, 1, 0, 0, 0).to_std_timepoint())
+   {
+   /*
+   * Technically any time step except 0 is valid, but 30 is typical
+   * and over 5 minutes seems unlikely.
+   */
+   if(m_time_step == 0 || m_time_step > 300)
+      throw Invalid_Argument("Invalid TOTP time step");
+   }
+
+uint32_t TOTP::generate_totp(std::chrono::system_clock::time_point current_time)
+   {
+   const uint64_t unix_time =
+      std::chrono::duration_cast<std::chrono::seconds>(current_time - m_unix_epoch).count();
+   return this->generate_totp(unix_time);
+   }
+
+uint32_t TOTP::generate_totp(uint64_t unix_time)
+   {
+   return m_hotp.generate_hotp(unix_time / m_time_step);
+   }
+
+bool TOTP::verify_totp(uint32_t otp, std::chrono::system_clock::time_point current_time,
+                       size_t clock_drift_accepted)
+   {
+   const uint64_t unix_time =
+      std::chrono::duration_cast<std::chrono::seconds>(current_time - m_unix_epoch).count();
+   return verify_totp(otp, unix_time, clock_drift_accepted);
+   }
+
+bool TOTP::verify_totp(uint32_t otp, uint64_t unix_time,
+                       size_t clock_drift_accepted)
+   {
+   uint64_t t = unix_time / m_time_step;
+
+   for(size_t i = 0; i <= clock_drift_accepted; ++i)
+      {
+      if(m_hotp.generate_hotp(t-i) == otp)
+         {
+         return true;
+         }
+      }
+
+   return false;
+   }
+
+}