LECTURE 15: NOTES ON Quantum Cryptography

One: hard problems in mathematics
Breaking the system requires an efficient algorithm for solving a hard problem – e.g. Factoring large numbers, discrete logarithms
Examples: RSA, El Gamal
Used in public key systems
Slow
Two: information theory
Texts scrambled by repeated application of bit shifts and permutations
Examples: DES, AES
Used in private key systems
Fast
Quantum Cryptography
is one of the new field in the cryptography to design the system promises of new level of security in the communication system

Protect against attack by quantum computer
or any future machine
Eavesdropping detection
Hard to do now
High volume key distribution
If it can be made fast enough
Basis – frame of reference for quantum measurement
Example – polarization vertical/horizontal vs. diagonal
Horizontal filter, light gets through = 0
Vertical filter, light gets through = 1
45 deg. filter, light = 0
135 deg. filter, light = 1

It is not possible to create perfect copies of a quantum state in transit for the purpose of measurement, while sending on the original. Consequently, current practical quantum cryptography set-ups are point to point based or at best within a Local Area Network since optical fiber amplifiers cannot be used.