Method and system for encrypting streamed data employing fast set-up single use keys and self-synchronization. A transmitting handset produces a bitstream of voice data containing the session key and encrypted by an encryption signal based upon the session key. A receiving handset decrypts the incoming bitstream using the encryption signal and recognizes the session key, thereby establishing synchronization. The session key is derived from a seed by applying a first function to the seed. Following the call, the session key is converted into a new seed by application of a second function and the new seed is stored for use in the next call.