"Towards Perfect Ciphers --- Quantum Cryptography."

[David Farber <farber () central cis upenn edu>]

        The upcoming Modern Optics and Spectroscopy Seminar
        on December 7 is of special interest to the Physics of
        Computation community:


                        Tuesday, 7 December 1993
                        11:00 -- 12:00 AM
                        Room 37-252 (Marlar Lounge)


        "Towards Perfect Ciphers --- Quantum Cryptography."


                        Artur K. Ekert
                        Oxford University


Cryptography has, for a long period of time, been regarded as a part
of mathematics, with computational difficulty as a safeguard of
information. Unfortunately, faster computers and better algorithms
have step by step cracked the protection barriers of even the most
sophisticated codes. The quest for unbreakable ciphers had to venture
outside mathematics, and surprisingly, towards quantum physics [1].


I will discuss the overlap between different theoretical and
experimental techniques developed independently by research groups
working in secure communication and quantum physics. In particular I
will present a method in which the security of the so-called key
distribution and also the key storing processes in cryptography relies
on quantum correlations [2]. The proposed scheme is based on Bohm's
well-known version of the Einstein-Podolsky-Rosen gedankenexperiment
and has been currently implemented using the Mach-Zehnder
interferometer [3].


REFERENCES


[1] For a simple introduction to quantum cryptography see
    BENNET_CH, BRASSARD_G, EKERT_AK  "Quantum Cryptography"
    SCIENTIFIC AMERICAN 1992 OCTOBER PP.50-59;
    EKERT_AK  "Quantum Keys for Keeping Secrets"
    NEW SCIENTIST 16 JANUARY 1993 PP.24-28.


[2] EKERT_AK  "Quantum Cryptography Based on Bell's Theorem"
    PHYSICAL REVIEW LETTERS 1992 VOL.67 PP.661-663.


[3] EKERT_AK, RARITY_JG, TAPSTER_PR, PALMA_GM
    "Practical Quantum Cryptography Based on 2-Photon Interferometry"
    PHYSICAL REVIEW LETTERS 1992 VOL.69 NO.9 PP.1293-1295.