<?php

/**

 * Returns OTP data. Numeric except for public and private IDs, which are hex.

 * @return array Associative

 */

function yms_decode_otp($otp, $key)

{

  static $aes = false;

  if ( !is_object($aes) )

    $aes = AESCrypt::singleton(128, 128);

  $return = array();

  $otp = yms_tobinary($otp);

  if ( strlen($otp) != 22 )

  {

    return false;

  }

  $key = yms_tobinary($key);

  if ( strlen($key) != 16 )

  {

    return false;

  }

  $cryptpart = yms_hex_encode(substr($otp, 6, 16));

  $publicid = substr($otp, 0, 6);

  $return['publicid'] = yms_hex_encode($publicid);

  $otp_decrypted = $aes->decrypt($cryptpart, $key, ENC_HEX);

  $crc_is_good = yms_validate_crc($otp_decrypted);

  $return['privateid'] = yms_hex_encode(substr($otp_decrypted, 0, 6));

  $return['session'] = yms_unpack_int(strrev(substr($otp_decrypted, 6, 2)));

  $return['timestamp'] = yms_unpack_int(strrev(substr($otp_decrypted, 8, 3)));

  $return['count'] = yms_unpack_int(substr($otp_decrypted, 11, 1));

  $return['random'] = yms_unpack_int(substr($otp_decrypted, 12, 2));

  $return['crc'] = yms_unpack_int(substr($otp_decrypted, 14, 2));

  $return['crc_good'] = $crc_is_good;

  return $return;

}

function yms_unpack_int($str)

{

  $return = 0;

  for ( $i = 0; $i < strlen($str); $i++ )

  {

    $return = $return << 8;

    $return = $return | ord($str{$i});

  }

  return $return;

}

function yms_crc16($buffer)

{

  $buffer = yms_tobinary($buffer);

  $m_crc=0x5af0;

  for($bpos=0; $bpos<strlen($buffer); $bpos++)

  {

    $m_crc ^= ord($buffer[$bpos]);

    for ($i=0; $i<8; $i++)

    {

      $j=$m_crc & 1;

      $m_crc >>= 1;

      if ($j) $m_crc ^= 0x8408;

    }

  }

  return $m_crc;

}

function yms_validate_crc($token)

{

  $crc = yms_crc16($token);

  return $crc == 0;

}

function yms_within($test, $control, $fuzz)

{

  $min = $control - $fuzz;

  $max = $control + $fuzz;

  return $test > $min && $test < $max;

}