Since its invention in 1984, the quantum key distribution algorithm developed by Charles Bennett and Gilles Brassard has been an industry standard for educational purposes.
The BB84 algorithm essentially allows generating identical random binary sequences for two remote parties traditionally called Alice and Bob. Its unique feature is that any interference with the process of sequence generation will be noticed by legitimate users. This allows us to use the BB84 algorithm to generate secret keys used in symmetric-key cryptography algorithms. The most prominent example of such algorithms is the Vernam cipher – the only one with proven perfect secrecy.
Here is how the BB84 works:
- Alice generates a random binary number in a random basis and sends it to Bob.
- Bob randomly chooses a basis to measure it in.
- Alice and Bob repeat this process until they have enough raw key length.
- Alice and Bob publicly announce their bases choices and discard all the discrepancies. This process is called sifting.
- Alice and Bob open and compare a part of the sifted key. If the number of errors is below a certain threshold they can be sure that the key distribution process was secure.
You will learn the practical implementation of BB84 after you complete the remote lab.