I have once again come across an IT department who were/are firmly convinced that the commercial web application that they use is secure and has encrypted user details. What it actually does is Base64 encode the password. This is not encryption and must be treated as plaintext.
So what is Base64 encoding and why do we have it? Well, a large number of popular application layer protocols are ASCII text based, i.e. they transfer plain text over the network. A good example of this is HTTP - the protocol used to transfer HTML (or Web) pages around. Originally, only text pages were sent with markup embedded to style it. However, soon other resources were added to the web including pictures, documents, etc. HTTP is designed to transfer plain ASCII text, so how do you transfer a JPEG photograph? Answer: You convert it into plain ASCII text.
The basic principle of converting a file into text is to use the data to represent an index to the ASCII character, e.g. 'A' is 63, 'B' is 64, 'a' is 97, '8' is 56, etc. So, if the first four bytes of your file are 63, 64, 97 and 56, this can be represented by 'ABa8' without loss. However, ASCII is actually only 7 bits and we usually use 8-bit bytes (because of IBM setting the standard - actually a byte was historically just the number of bits required to store a character). Also, ASCII character 13 is a carriage return, 27 is escape and 8 is backspace. These are non-printable and, worse than that, could corrupt the communications as well as remove other characters. So, we can't just do a straight conversion from bytes to ASCII.
This is where Base64 conversion comes in. We split the file up into 6-bit 'bytes', rather than 8-bit. 6 bits give us 64 possible values. These are then represented by the digits, upper and lowercase letters and a couple of symbols ensuring that they are always printable and don't cause problems. So, the Base64 encoded password is just a 6-bit 'byte' representation of an 8-bit byte password and it is trivial to convert between the two. There is no security in Base64 encoding anything. Perhaps I should repeat that again.
Base64 encoding something is not encrypting it and provides NO SECURITY whatsoever!
I am constantly surprised and disappointed that people think that Base64 encoding something will protect it. I know TLS has its problems, but why aren't all web applications using it?