Appendix: “Mutual Preparation Algorithm” for Quantum Cryptography

Abstract

Firstly, Alice (the sender of the message) with her private key 1 generates a sequence consisting of (+)-or (-)-symbols, which correspond to the instantaneous alignment of her "transmitter", e.g., an optical polarizer. The instantaneous polarization can be horizontally/vertically (0 • /90 • , ˆ = ˆ S z) or left/right diagonally (135 • /45 • , ˆ = ˆ S x). Next she publicly sends to Bob (the receiver)-for their mutual preparation of the encoding of the message to follow-a data set consisting of a long random sequence of (0)-or (1)-bits, a test message, where the bits of the (0/1)-sequence are closely correlated to the (+/-)-sequence according to the following rules. The test message contains at the position n either a "1", e.g., for vertical polarization, P = 90 • , and for right-diagonal polarization, P = 45 • ; or a "0" for horizontal polarization and for left-diagonal polarization, P = 0 • and P = 135 • .