quantum cryptography

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QUANTUM QUANTUM CRYPTOGRAPHY CRYPTOGRAPHY Jennifer Nalley Jennifer Nalley 2008 2008

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This is a PowerPoint about one of the possible applications of quantum entanglement. I made this PP for a tech writing class.

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Page 1: Quantum Cryptography

QUANTUMQUANTUMCRYPTOGRAPHYCRYPTOGRAPHY

Jennifer NalleyJennifer Nalley20082008

Page 2: Quantum Cryptography

CryptographyCryptography

κρυπτόσκρυπτόσ (kryptós) (kryptós)

““hidden”hidden”

++

γράφωγράφω (grápho) (grápho)

““write”write”

==

Hidden WritingHidden Writing

Page 3: Quantum Cryptography

Classic CryptographyClassic CryptographyEncrypt Encrypt (plaintext → cipher (plaintext → cipher text) text) Transmit cipher textTransmit cipher textDecrypt (Decrypt (cipher text → cipher text → plaintext)plaintext)Secure for as long as the Secure for as long as the algorithm isalgorithm is

Page 4: Quantum Cryptography

Cryptography is an old art…Cryptography is an old art…A Transposition A Transposition

CipherCipher

(700 BC)(700 BC)

Page 5: Quantum Cryptography

Modern CryptographyModern Cryptography

Early computer cryptosystems used mathematical complexities to provide securityMultiplying 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)

Page 6: Quantum Cryptography

Quantum Cryptography is Superior…Quantum Cryptography is Superior…Because it is UNBREAKABLEBecause it is UNBREAKABLE

Quantum Cryptography Quantum Cryptography

obtains its fundamentalobtains its fundamental

security from the factsecurity from the fact

that each Q-bit isthat each Q-bit is

carried by a singlecarried by a single

photon, and photon, and eacheach

photon will be altered photon will be altered

as soon as it is read.as soon as it is read.

(a side effect of (a side effect of quantum behavior) quantum behavior)

This makes it This makes it impossibleimpossible to to intercept message intercept message without being without being detecteddetected. .

Page 7: Quantum Cryptography

Heisenberg Uncertainty Principle and Heisenberg Uncertainty Principle and Quantum MechanicsQuantum Mechanics

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

Page 8: Quantum Cryptography

Polarized LightPolarized LightWhen measuring the When measuring the polarization of a photon, polarization of a photon, the choice of what the choice of what direction to measure direction to measure affects all subsequent affects all subsequent measurements.measurements.

If a photon passes If a photon passes through a vertical filterthrough a vertical filter

it will have the vertical it will have the vertical orientation regardless orientation regardless of its initial direction of of its initial direction of polarizationpolarization. .

Page 9: Quantum Cryptography

In all……In all……

Taking into account the use of polarized light….recall

that:Quantum Cryptography obtains its fundamentalsecurity from the factthat each Q-bit iscarried by a singlephoton, and eachphoton 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.

Page 10: Quantum Cryptography

And….to go into further detail Would require some Would require some

mathematics some of you mathematics some of you may not enjoymay not enjoy

…….not to mention the time .not to mention the time issue. issue.

Had I thought ahead, I Had I thought ahead, I would have covered would have covered something like,“ The something like,“ The physics of roller-skating”.physics of roller-skating”.