Flip-KLJN: Random Resistance Flipping for Noise-Driven Secure Communication

The information-theoretically (unconditionally) secure Kirchhoff-law-Johnson-noise (KLJN) bit exchange protocol uses two identical resistor pairs with high (H) and low (L) resistance values, driven by Gaussian noise generators emulating Johnson noise with a high common temperature. The resulting mean-square noise voltage on the wire connecting Alice and Bob has three levels: low ( L/L ), intermediate ( H/L or L/H ), and high ( H/H ), and secure key sharing is achieved at the intermediate level ( L/H or H/L ). This paper introduces the Flip-KLJN scheme, where a pre-agreed intermediate level, such as H/L , triggers a flip of the bit map value during the bit exchange period. For Eve, the bit map flips appear random. Thus, the formerly discarded H/H and L/L situations can also have a pre-agreed bit value mapping, which flips together with the original bit mapping. Thus, Flip-KLJN doubles the key rate and ensures that all three levels on the wire are indistinguishable for Eve. Bit error probabilities are addressed through analytic calculations and computer simulations.