The document discusses quantum cryptography, highlighting its unbreakable nature due to the alteration of photons when measured, which prevents message interception without detection. It explains the relationship between quantum mechanics and encryption, particularly focusing on the Heisenberg Uncertainty Principle and the concept of particle entanglement. The text contrasts traditional cryptography's reliance on mathematical complexity with the inherent security of quantum systems.

1. QUANTUM CRYPTOGRAPHY Jennifer Nalley 2008

2. Cryptography κρυπτόσ (kryptós) “ hidden” + γράφω (grápho) “ write” = Hidden Writing

3. Classic Cryptography Encrypt (plaintext -> cipher text) Transmit cipher text Decrypt ( cipher text -> plaintext) Secure for as long as the algorithm is

4. Cryptography is an old art… A Transposition Cipher (700 BC)

5. Modern Cryptography Early computer cryptosystems used mathematical complexities to provide security Multiplying two huge prime numbers is quick, but factoring such a composite number is computationally intensive….(even for a computer) As computer technologies advance, mathematical complexity may not be a guarantee for security ….(Someone in Derrick Hall could crack today's best code, and rob us all)

6. Quantum Cryptography is Superior…Because it is UNBREAKABLE Quantum Cryptography obtains its fundamental security from the fact that each Q-bit is carried by a single photon, and each photon will be altered as soon as it is read. (a side effect of quantum behavior) This makes it impossible to intercept message without being detected .

7. Heisenberg Uncertainty Principle and Quantum Mechanics TERMINOLOGY: Observable- some measurable feature of a quantum particle. Examples of observables include: a particle’s position (where the particle is), momentum (classically equal to mass x velocity) In the quantum world, nothing is certain: Measurement CAN NOT be made without perturbation. Heisenberg uncertainty principle does not allow for conjugate values of precision (for any two observables). Specifically, the act of obtaining a measurement of one observable, limits the degree of certainty on any second measurement. ( ∆E∆t ≥ ħ). Sometimes two particles can become “ENTANGLED”. When this occurs, act of measuring an observable on one particle…..seems to instantaneously determine the orientation of the second. This is strange, but utilizable. Consider polarized light

8. Polarized Light When measuring the polarization of a photon, the choice of what direction to measure affects all subsequent measurements. If a photon passes through a vertical filter it will have the vertical orientation regardless of its initial direction of polarization .

9. In all…… Taking into account the use of polarized light….recall that: Quantum Cryptography obtains its fundamental security from the fact that each Q-bit is carried by a single photon, and each photon will be altered as soon as it is read. We have an indeterminate system, one that carries information. An act done at will to one “part” of the system… determines the outcome of the other. We have an ideal set-up for securing information .

10. And….to go into further detail Would require some mathematics some of you may not enjoy … .not to mention the time issue. Had I thought ahead, I would have covered something like,“ The physics of roller-skating”.