--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/yms/libotp.php	Fri Jul 31 23:51:08 2009 -0400
@@ -0,0 +1,84 @@
+<?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;
+}