Encryption Protocol Sensitive to Eavesdroppers

Researchers at the Jet Propulsion Laboratory in Pasadena, Calif., Los Alamos National Laboratory in New Mexico and the University of Illinois at Urbana-Champaign have demonstrated a six-state protocol that makes eavesdroppers on quantum encrypted signals easier to detect. Four-state methods use entangled photons to convey binary data by fixing the linear polarization in either the horizontal/vertical direction or 45°/-45° to represent zeros and ones. To decode a message sent in this manner, a receiver would have to know which pairing is used, and any interception of the message would interfere with the final outcome -- indicating the presence of an eavesdropper.

The researchers introduced another pair of states, right and left circular polarization. In the July 12 issue of the New Journal of Physics, they reported that the extra pair make the encryption method significantly more sensitive to eavesdroppers but technically harder to perform. Although it introduces more data loss into a message, they expect that disadvantage to be eliminated if quantum memory systems can be incorporated.