totp.cpp

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/*
* TOTP
* (C) 2017 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
 
#include <botan/otp.h>
#include <botan/internal/calendar.h>
 
namespace Botan {
 
TOTP::TOTP(const uint8_t key[], size_t key_len,
           std::string_view hash_algo,
           size_t digits, size_t time_step)
   : m_hotp(key, key_len, 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.
   */
   BOTAN_ARG_CHECK(m_time_step > 0 && m_time_step < 300, "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;
   }
 
}