In the face of brute force, known, plaintext attacks, the required number of ciphertext copies physically generated (by beam splitters, for example) for successful attack on the key can easily be made greater than the number of elementary particles in the universe. Once a quantum computer becomes available, even Grover’s quantum search algorithm could not reduce that requirement to a practical reality. This form of security is called exponential security and is prevalent in currently deployed cryptographic protocols. Physical-layer quantum encryption buttresses existing mathematical-complexity-based encryption security to deliver ultrasecure, high-data-rate, long-range, opticalbackbone- to-tactical communications that are readily incorporated into existing optical networks.

The AlphaEta protocol is a product of NuCrypt, LLC, a small high-tech company founded by Professor Prem Kumar, of Northwestern University (Evanston, Illinois). AlphaEta is based principally upon the KCQ ideas of Prof Horace Yuen, also of Northwestern University. Northwestern University researchers developed AlphaEta through the recently initiated Defense Advanced Research Projects Agency (DARPA) Quantum Information Science and Technology program. Operating AlphaEta at 1550 nm wavelengths and 622 Mbps, Telcordia® Technologies, Inc., successfully demonstrated it on existing fiber-optic networks existing in the Advanced Technology Demonstration Network (near Washington DC) and linked to the Boston South Network (in Boston, Massachusetts) via New York City, a distance of approximately 850 km. Ciena® Government Solutions, Inc., demonstrated AlphaEta on a 550 km fiber-optic network connecting Argonne National Laboratory with the National Center for Supercomputing Applications at the University of Illinois at Urbana- Champaign.

DARPA and an AFRL and Air Force Space and Missile Center consortium awarded NuCrypt parallel Small Business Innovation Research contracts. These efforts are concentrating on wired quantum communications and wireless quantum communications, respectively. The company is developing systems with communication bit rates ranging from 100 Mbps to several Gbps, since scalability is a desirable capability for interoperability among disparate communications platforms. Meanwhile, AFRL also awarded NuCrypt a Small Business Technology Transfer Phase I contract to investigate the use of recent advances in short-pulse laser physics to enhance the considerable physical-layer security AlphaEta already offers. The objective of this basic research activity is to achieve near-perfect informationtheoretical security, allowing ultrasecure, remote, secret key distribution at high data rates and long ranges in existing wireless and wired optical networks.

Dr. David H. Hughes, of the Air Force Research Laboratory’s Information Directorate, wrote this article. For more information, contact TECH CONNECT at (800) 203-6451 or place a request at http://www.afrl.af.mil/techconn_index.asp. Reference document IF-H-06-04.

References

¹ Bennett, C. and Brassard, G. “Quantum Cryptography: Public-Key Distribution and Coin Tossing.” Proceedings of the IEEE International Conference on Computers, Systems, and Signal Processing. Bangalore, India, 1984 (IEEE Press, 1984): 175-179.
² Shor, P. and Preskill, J. “Simple Proof of Security of the BB84 Quantum Key Distribution Protocol.” http://arxiv.org/ PS_cache/quant-ph/pdf/0003/0003004.pdf.
³ Yuen, H., et al. “Security of Y-00 and Similar Quantum Cryptographic Protocols.” Quantum Physics Abstract (quantph/ 0407067). http://xxx.lanl.gov/PS_cache/ quant-ph/pdf/0407/0407067.pdf.
⁴ Yuen, H. “KCQ: A New Approach to Quantum Cryptography I. General Principles and Key Generation.” Quantum Physics Abstract (quant-ph/0311061). http://xxx.lanl.gov/PS_cache/quant-ph/ pdf/0311/0311061.pdf.
⁵ Barbosa, G., et al. “High-speed data encryption over 25 km of fiber using twomode coherent-state quantum cryptography.” Optics Letters, vol 28, no 21 (2003): 2040-2042.
⁶ Corndorf, E., et al. “Quantum-Noise- Protected Data Encryption in a WDM Network.” IEEE Photonics Technology Letters, vol 17, no 7 (Jul 05): 1573-1575.