quantum cryptography n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Quantum Cryptography PowerPoint Presentation
Download Presentation
Quantum Cryptography

Loading in 2 Seconds...

play fullscreen
1 / 25

Quantum Cryptography - PowerPoint PPT Presentation


  • 172 Views
  • Uploaded on

Quantum Cryptography. By Taipan Tamsare. Outline. Motivation Quantum Physics Polarization Quantum Cryptography Eavesdropping and Detection Current State Affairs Summary. Motivation. Why Quantum Cryptography? Nearly Impossible to steal Detect if someone is listening “Secure”.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Quantum Cryptography' - isanne


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
quantum cryptography

Quantum Cryptography

By

TaipanTamsare

outline
Outline
  • Motivation
  • Quantum Physics
  • Polarization
  • Quantum Cryptography
  • Eavesdropping and Detection
  • Current State Affairs
  • Summary
motivation
Motivation
  • Why Quantum Cryptography?
    • Nearly Impossible to steal
    • Detect if someone is listening
    • “Secure”
quantum physics
Quantum Physics
  • Light waves are propagated as discrete particles known as photons.
  • Polarization of the light is carried by the direction of the angular momentum, or spin of the photons.
slide5

b

ψ

a

Polarized photons

  • Polarization can be modeled as a linear combination of basis vectors vertical () and horizontal ()
  • A quantum state of a photon is described as a vector
    • quantum cryptography often uses photons in 1 of 4 polarizations (in degrees): 0, 45, 90, 135
polarization by a filter

Vertically polarized light

Unpolarized light

Filter tilted at angle q

Vertical aligned filter

Polarization by a Filter
quantum cryptography1
Quantum Cryptography
  • Two physically separated parties can create and share random secret keys.
  • Allows them to verify that the key has not been intercepted.
  • Quantum Key Distribution(QKD)
bb84 qkd protocol
BB84 QKD protocol
  • Alice
    • Encodes her information randomly in one of the two bases…
      • For example,
slide12
BB84

Alice prepares 16 bits

0101100010101100

in the following bases,

BAABAABAAAABBBBA

Thus the following states are sent to Bob:

+10-10+0101+--+0

slide13
BB84

Bob receives the stream of qubits and measures each one in a random basis:

ABAABAAABABBBBAB

slide14
BB84

So Bob gets

1-00-0+0+0-+--1+

slide15
BB84
  • Then Alice and Bob compare their measurement bases, not the results, via a public channel.
slide16
BB84
  • So Bob and Alice are left with 7 useable bits out of 16

_ _ 0 _ _ 0 _ 0 _ 0_ 0 1 1 _ _

These bits will be the shared key they use for encryption.

slide17

Eavesdropping

  • Now enter Eve… She wants to spy on Alice and Bob.
  • So she intercepts the bit stream from Alice, measures it, and prepares a new bit stream to Bob based on her measurements…
eavesdropping1
Eavesdropping
  • Eve has to re-send all the photons to Bob
  • Will introduce an error, since Eve don't know the correct basis used by Alice
  • Bob will detect an increased error rate
eavesdropping2
Eavesdropping
  • Thus, of the bits Bob measures in the correct bases, there is 50% that eve had changed the basis of the bit. And thus it is equally likely that Bob measure 0 or 1 and thus an error is detected 25% of the time.
detecting eavesdropping
Detecting Eavesdropping
  • When Alice and Bob need to test for eavesdropping
  • By randomly selecting a number of bits from the key and compute its error rate
  • Error rate < Emax assume no eavesdropping
  • Error rate > Emax assume eavesdropping(or the channel is unexpectedly noisy)Alice and Bob should then discard the whole key and start over
slide22

Current State of Affairs

  • Commercial quantum key distribution products exist
slide23

Current State of Affairs

  • Current fiber-based distance record: 200 km
slide24

Summary

  • The ability to detect eavesdropping ensures secure exchange of the key
  • The use of one-time-pads ensures security
  • Equipment can only be used over short distances
  • Equipment is complex and expensive
slide25

References

  • Zelam Ngo, David McGrogan
  • Biometrics and Cryptography UTC/CSE
  • VasilPenchev, Assoc. Prof., PhD