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Quantum Cryptography

Quantum Cryptography. (Quantum Cryptography). The BIG Idea. Basic idea of cryptography – To keep information secure from prying eyes.

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Quantum Cryptography

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  1. Quantum Cryptography (Quantum Cryptography)

  2. The BIG Idea • Basic idea of cryptography – To keep information secure from prying eyes. • Current encryption is mathematically based. Basically there are several possible types of keys and if the sender and end user both know the key, they can exchange information securely.

  3. Why Quantum? • Current encryption standards for a 128-bit key mean that there are over 1 x 10^35 possible combinations. • Despite that, with the possibility of quantum computers, this number of possible solutions may not always take an inordinate amount of time for a computer to test, as it does today.

  4. How It’s Done • A main type of quantum cryptography was proposed by Bennett and Brassard in 1984. The main idea is one of polarization (such as that of photons).

  5. The Quantum Story • The traditional analogy is one of wanting to send an encrypted message between A and B without being eavesdropped upon by an outsider. The sender of the information is represented by Alice (A), the recipient by Bob (B) and the eavesdropper is called Eve. • Depending on the state of the photon and of the polarizer, the photon bit can represent a 1 or a 0.

  6. Meat of the Story • There are multiple possible orientations of polarization (think of possible vertical and horizontal [+], and diagonal [X] orientations). • As photons are sent by Alice, they pass through a polarizer, either + or X, and as they arrive at Bob they pass through another polarizer. Since he doesn't know the orientation of polarization, he randomly puts a filter (also either + or X) at his end. Some of the photons are able to pass through and others are not. The act of reading the orientation of a photon changes it!

  7. Spookiness…

  8. How Does It Work? • So if the 'quantum key' has been intercepted, the % of the time that Alice and Bob will agree on the photon orientation and polarizer used will differ from the expected % (75% in what I researched), and they'll know that some other interaction with the photons has happened in between – eavesdropping!!

  9. Secure? • Alice and Bob can communicate whether or not the photons agree by using a classical channel (unsecured). Bob can indicate which polarizer he used and what the end result of his photons were (a 1 or 0). Alice cross references the information from Bob and they can ignore the bits of information for which they used the incorrect polarizer. • They should agree on 100% of the bits for which they agree of the method of transmission. If not, it's due to interference in between.

  10. When? • Today! Quantum Cryptography is not just theoretical, it really exists! • Transmission can either be direct or through a fiber optic cable • Limitations on length of transmission are due to impurities in the fiber optic cable or inherent uncertainties (Quantum again!) in direct transmission.

  11. An example:

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