C191: Quantum Cryptographycs191/fa10/notes/qcrypto.pdf · BB84 Protocol for Key Distribution Repeat...
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C191: Quantum Cryptography Umesh V. Vazirani
Transcript of C191: Quantum Cryptographycs191/fa10/notes/qcrypto.pdf · BB84 Protocol for Key Distribution Repeat...
C191: Quantum Cryptography
Umesh V. Vazirani
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How to agree on a secret key?
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Quantum Crypto Setup
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RSA: Public-key Cryptography
Alice Bob
• Alice publishes public key = (N, e).
• N = PQ, with P, Q primes known only to Alice.Her private key is d: de = 1 mod (P-1)(Q-1)
• Ed = mde = m (mod N)
• Eavesdropper Eve doesn’t know d, and cannot decrypt.
message mE= me mod N
Decrypts: m = Ed
• Unconditional security
• Quantum factoring breaks RSA!
• Has been implemented using today’s technology
• Measurement disturbs the system
- detect eavesdropper
Why Quantum Cryptography?
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Photon Polarization
• The polarization of a photon is a direction in the plane normal to the direction of propagation.
• The polarization of a photon is a qubit.
• A polarizing filter blocks photons whose polarization is perpendicular to the orientation of the filter and transmits photons whose polarization is aligned with the orientation of the filter.
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