I just had the idea for another encryption algorithm, and because there are that few of them :-) I want to explain it.
First you define two bicjective functions working on bit arrays (A and B).
Then for every bit of the key you choose A or B (1->A 2-B) and apply them to the source Text.
If A and B are defined the right way (the "baeckertransformation" is a good start), you can mix the bits in ways that the result is allways statistical random numbers (at least for each random number test I know or wich i could find on Wikipedia :-) )
Advantage is, that you can use every blocksize and every key size you want.
Disadvantage is, that the encryption algorithm is vers slow.
Because a few thousend years ago already some very intelligent people thought about cryptography: Who did encryption like this before? What keywords should I google for?