 If Eve is assumed to have unlimited resources, for example both classical and quantum computing power, there are many more attacks possible.BB84 has been proven secure against any attacks allowed by quantum mechanics, both for sending information using an ideal photon source which only ever emits a single photon at a time, and also using practical photon sources which sometimes emit multiphoton pulses.These proofs are unconditionally secure in the sense that no conditions are imposed on the resources available to the eavesdropper; however, there are other conditions required