I'd like to implement a "Product Registration" scheme into my software where upon initial use, the User must enter a key to unlock it.
The key they enter is compared to their encrypted Username.
They would have to acquire the key from myself if they wished to use the software. Their encrypted Username must be reasonably short so it's not too difficult for them to enter the key. They would however, only have to enter the key once.
(I'm aware this isn't actually how keys are issued)
What kind of encryption is appropriate for this?
(It needs to encrypt a string into letters and numbers only and be reasonably short).
There's no thought needed over decryption, since I'll only be comparing encrypted strings.
I'm basically looking for a cipher that produces the shortest code possible so that it's not tedious for the User to enter. (Though still difficult to break)
(You needn't worry over the actual security.
I'm a noob programmer and all my software is free anyway)