Editing BB84 Quantum Key Distribution (section)

==Outline==
The protocol shares a classical key between two parties, Alice and Bob.
The BB84 quantum key distribution protocol consists of the following steps:
*'''Distribution:''' This step involves preparation, exchange and measurement of quantum states. For each round of the distribution phase, Alice randomly chooses a basis (a pair of orthogonal states) out of two available bases (X and Z). She then randomly chooses one of the two states and prepares the corresponding quantum state in the chosen basis. She sends the prepared state to Bob. Upon receiving the state, Bob announces that he received the state and randomly chooses to measure in the either of the two available bases (X or Z). The outcomes of the measurements give Bob a string of classical bits. The two parties repeat the above procedure <math>n</math> times so that at the end of the distribution phase each of them holds an <math>n</math>-bit string.
*'''Sifting:''' Alice and Bob publicly announce their choices of basis and compare them. They discard the rounds in which Bob measured in a different basis than the one prepared by Alice.
*'''Parameter estimation:'''  Alice and Bob use a fraction of the remaining rounds (in which both measured in the same basis) in order to estimate the [[quantum bit error rate]] (QBER).
*'''Error correction:''' Alice and Bob choose a classical error correcting code and publicly communicate in order to correct their string of bits. At the end of this phase Alice and Bob hold the same bit-string.
*'''Privacy amplification:''' Alice and Bob use an [[extractor]] on the previously established string to generate a smaller but completely secret string of bits, which is the final key.