HTML
<?php echo htmlspecialchars("This & that are <problems>.");?>
Output
This & that are <problems>.
Base64
<?php
 $encoded = base64_encode("A rose by any other name...");
 $decoded = base64_decode($encoded);
 echo "$encoded<br />$decoded";
?>
Output
QSByb3NlIGJ5IGFueSBvdGhlciBuYW1lLi4u
A rose by any other name...
Others
MD5, DES, TripleDES, Blowfish, 3-WAY, SAFER-SK64, SAFER-SK128, TWOFISH, TEA, RC2, GOST in CBC, OFB, CFB and ECB cipher modes as well as RC6 and IDEA