Base-64 encoding is a way of taking binary data and turning it into text so that its more easily transmitted in things like e-mail and HTML form data. (WikiPedia)
You can re-encode for X amount of time. You can also do the same for decode.
The MD5 message-digest algorithm is a widely used hash function producing a 128-bit hash value. Although MD5 was initially designed to be used as a cryptographic hash function, it has been found to suffer from extensive vulnerabilities. (WikiPedia)
In cryptography, SHA-1 is a cryptographic hash function which takes an input and produces a 160-bit hash value known as a message digest – typically rendered as a hexadecimal number, 40 digits long. It was designed by the United States National Security Agency, and is a U.S. Federal Information Processing Standard. (WikiPedia)