password encryption

if i was to create a password that is only one letter, lets say "X", and a website uses a 128bit encryption... how does that work?
can someone explain please?
I understand that with a 128bit encryption there could be 2to the power of 128 possible combinations to crack a password, but how is that possible if I'm using only one letter as a password?
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Kyle AbrahamsSenior .Net DeveloperCommented:
So a 128 bit key is used to generate a cypher text from the "X".  That cypher text is then passed and only the key can correctly decrypt the cypher back to "X".  Using a different key could produce other results such as "y" or nothing meaningful at all.  The 128 bit has to do with the length of the key, and hence the number of possibilities used to brute force that key, not the length of what you're encrypting / decrypting.
MrMayAuthor Commented:
Kyle, can u please explain this a bit further.
A cipher is a combination of both the encryption and decryption algorithm, right?
A 128 bit key is basically 128 0s and 1s, right?
I don't quite understand how a 128 bit key ties in the actual password...
Kyle AbrahamsSenior .Net DeveloperCommented:
A cipher is the result of the encryption algorithm, which is then used during the decryption algorithm.

The 128 bit key transforms the clear text to cipher during the encryption phase.
The 128 bit key transforms the cipher back to clear text during the decryption phase.

This is according to the use of symmetric key encryption.  It's different with PKI or assymetric encryption (as in the keys are different).

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