1. IIS 2004, CroatiaSeptember 22, 2004 Quantum Cryptography and Security of Information Systems dalibor.hrg@quantum.at 1 leo.budin@fer.hr 2 marin.golub@fer.hr 2 15 th International conference on Information and Intelligent Systems IIS 2004, Varazdin, Croatia Quantum Experiments and the Foundations of Physics, Vienna 1 University of Zagreb, Faculty of Electrical Engineering and Computing 2

2. IIS 2004, CroatiaSeptember 22, 20042/13 Overview Problems in cryptography (key distribution, quantum algorithm for fast factorization) What is Quantum Cryptography (QC)? (quantum key distribution, protocols: BB84 and EPR) Technology and current status (quantum optics and fibers, first BB84 commercial product in 2002, first application outside laboratory - world first bank transfer in Vienna 2004, EPR QC) Future considerations (EU SECOQC project with 11.4 million EUR investment, long distance Quantum Cryptography, Quantum networks, space applications,...) Who is working? (Vienna group, Geneva, Munich, BBN Tech., NIST, MIT,…)

3. IIS 2004, CroatiaSeptember 22, 20043/13 Problems in cryptography Alice and Bob want to communicate. Alice encrypts the message (3DES, IDEA) with a key. How can Bob receive the key, over a public channel and Eve, which is needed for decryption of the message? Today, only two practical solutions: Public Key Cryptography (PKC) and Quantum Key Distribution (QKD) often known as Quantum Cryptography (QC); Also, one not so practical solution: face-to-face meeting. Problem: PKC relies on unproven mathematical assumption - prime factorization is hard! Is it? It’s not! Shor’s quantum algorithm for fast prime factorization, 1994. Soon, it could be implemented! Market and companies want perfect security which doesn’t depend on computational power (quantum or classical computers)! QKD is the solution!

4. IIS 2004, CroatiaSeptember 22, 20044/13 What is Quantum Cryptography? Engineering Electronic circuits, digital electronics, FPGA, detectors. Physics Quantum mechanics, Quantum optics, photon sources, fibers, lasers. Computer Science and Mathematics Communication complexity, Computer networks, Cryptography, Quantum Information Theory. Method of simultaneous generation of a random key for secure data communication at two different locations, by measuring the appropriate properties of quantum particles, e.g. the polarisation of single or entangled photons. Today, in general, two main protocols: BB84 and EPR (Einstein Podolsky Rosen).

5. IIS 2004, CroatiaSeptember 22, 20045/13 A view on BB84 protocol (1/2) Proposed in 1984 by Charles H. Bennet (IBM) and Gilles Brassard (Montreal). Implemented in 1990, authors of BB84. Based on polarizations of single photons! First shown over 32 cm of free-space distance with LED. Today, many implementations, some over 50 km through free-space and fiber optics. Two channels: public channel (Internet or telephone) and quantum channel (optical fiber or a free-space optical link). Pulses of polarized light with single photon, only in theory. In experiments, one pulse - a few photons (not good). Photon is either vertically (90  ) or horizontally (0  ) polarized (base  ). In another base , we have diagonal polarization: photon is polarised either 45  or 135 . 4 possible states in which a photon could be prepared! Security is reached due to no-cloning theorem and Heisenberg’s uncertainty principle!

6. IIS 2004, CroatiaSeptember 22, 20046/13 A view on BB84 protocol (2/3)

7. IIS 2004, CroatiaSeptember 22, 20047/13 A view on BB84 protocol (3/3)

8. IIS 2004, CroatiaSeptember 22, 20048/13 A view on EPR protocol Proposed by Arthur Ekert (Oxford, now Cambridge UK) in 1991; implemented in 1999 by group of Prof. Zeilinger (Vienna). Using polarization of pairs of entangled photons (quantum mechanical property, EPR paradox: “do-on-photon1-and-get-on- photon2”, no one knows why it works, but it works! Also used in quantum teleportation experiments) Problems: on 100000 pairs of photons/s - 15000 entangled pairs + low efficiency of fiber optics (-0.2db/km) gives on 100km only ~ 500 pairs/s. Key rate after error correction ~ 1 kb/s. Needed more, close to ~ 1Mb/s! Limited distances ~ up to 23 km (for now). Advantages: single photons, inherent randomness, much secure than BB84, future technology for long distances. Jennewein et al. Quantum cryptography with entangled photons, 1999, Vienna.

9. IIS 2004, CroatiaSeptember 22, 20049/13 Technology and current status (1/2) BB84 is easy to implement by using weak laser pulses. Problems in generation of single photons - pulses often contain a few photons (weakness, all carry same information - bit, can be used by eavesdropper in beam splitting attack). Quantum channel information can be lost due to decoherence - error rate is increased, final key rate is decreased due to error correction methods. Problems in both BB84 and EPR protocol: key bit rate is ~ 1 kb/s. Needed more ~ 1 Mb/s! Current max. distance achieved with fibers is ~ 50 km (BB84). Free-space quantum channel: problems with photon detection due to atmospheric perturbations and ambient light. Current applications: ~ 2 km, can go up to 23 km (EPR QC). Experiments in progress. Work on quantum memories, quantum teleportation and quantum swapping - technology for long distance quantum communication; also for EPR Quantum Cryptography (both fiber and free-space).

10. IIS 2004, CroatiaSeptember 22, 200410/13 Technology and current status (2/2) First commercial product in 2002, ID Quantique - BB84 QC system over 67 km, weak laser pulses through optical fiber. World first bank transfer using EPR QC, Quantum Experiments and the Foundations of Physics group, Vienna, 2004. Word first quantum network based on BB84 QC system, BBN Technologies, 2004. Network connects Boston University and Harvard.

11. IIS 2004, CroatiaSeptember 22, 200411/13 Future considerations (1/2) Development of global secure network based on Quantum Cryptography - SECOQC project (11.4 million EUR), Sixth Framework Programme, Priority (2) of the EU (April 2004 - 2008), www.secoqc.net. Countries involved: Republic of Austria, Belgium, UK, Canada, the Chez Republic, the Kingdom of Denmark, the French Republic, the Federal Republic of Germany, the Italian Republic, the Russian Federation, the Kingdom of Sweden, and the Swiss Confederation. QSpace project: Quantum communication in space (hard but feasible), ESA project, important for applications of Quantum Cryptography on long distances ~ 1000 km. Development of Quantum networks and needed infrastructure: quantum memories, error correction algorithms and privacy amplification methods,… Work on enhancement of optical devices - detectors and sources of photons. Free Space II - free-space EPR QC in Vienna over 8 km

12. IIS 2004, CroatiaSeptember 22, 200412/13 Future considerations (2/2)8km FreeSpace II - The Next Generation EPR QC via free-space 7,2km 8km Kufner - Sternwarte Twintowers Millenniumstower

13. IIS 2004, CroatiaSeptember 22, 200413/13 Who is working? Quantum Cryptography in Vienna www.quantenkryptographie.at in Quantum Experiments and Foundations of Physics group - www.quantum.at. World first experimental quantum teleportation (1997), world first EPR QC (1999), world first bank transfer with EPR QC (2004, Vienna). Geneva group - Swiss Munich group - Germany NIST Companies: ID Quantique (in 2002, first commercial QC system, BB84 type ) and MagiQ BBN Technologies Recently connected two campuses (Boston University and Harvard, US) with QC - BB84 type, also developing quantum network infrastructure, 2004. Sponsored by DARPA. Many other groups in Europe (UK, Germany, Norway,…) and US (MIT, Stanford, BU, Harvard …)