Quantum Cryptography

Physics 43, SRJC.Spring 11May 9, 2011

Chris Wenrich

Homer Van Grinsimpson

aka SethVan Grinsven 

James Anderson

History Of Quantum Cryptography

-'Computable Numbers' published in 1936 by Alan Turing

-The computing industry saw that there was a barrier to how small circuits could get.

-In 1982 Richard Feynman suggested individual quantum systems could be used for computation.

-In 1985 David Deutsch introduces first description of a quantum computer. Where quantum effects were not a barrier but could be used to take computing forward in to a new era of power and speed.

Modern Era-In 1984 C H Bennett and G Brassard of IBM proposed the BB84protocol as a means of using quantum effects for cryptography.

-Artur Ekert in 1991 proposed using pairs of photons to encrypt keys.

- Then in 1998 Nicholas Gisin at theUniversity at Geneva was able to demonstrate the polarization of photons over many cables.

- Other specific types of photon pairing has been discovered recently and will be refined in the future!

Why Use Quantum Cryptography?

Quantum Cryptography allows two people or parties to communicat with eachother while feel their messages are secure. The two groups can authenticate eachothers messages and deciphere the codes while at the same time be able to tell whether there is an evesdropper present. Allow the devices to create cryptography messages might be expensive its a risk willing to take when you factor in the security of the messages being sent.

How it works:

• Alice and Bob wish to exchange info securely.• Eve is trying to evesdrop (get it?!)• The most common form of Quantum

Cryptography is Quantum Key Distribution (QKD)

• QKD is also the only form of commercial Q. Cryptography.

Quantum Key Distribution:        A source produces pairs of entangled photons.  These photons are seperated and sent to alice and bob.  Each pair has opposite spins (Either vertical / Horizontal or -45/45 Degress) These sequence of electrons forms a code.  Alices code is opposite from Bobsan Example would be [Vertical = V         Horizontal = H            45 = +            -45 = -]

Alice: VH++HV-Bob  : HV--Vh+

How it Works Continued

The code is then sent to Bob and Alice, where a computer seperates the electrons and assigns numbers for each polarization.  example +45 and V = 1, H and -45 = 0.  Note that bob's and alice's code would be opposite. 

Bob then reverses his code to match Alices.  Now they have exact matches.  These codes are unique to alice and  bob.

How it Works Continued

If eve were to intercept the key, by reading and measuring the photons eve changes the polarity of them.  Thus, the code that were sent to alice would be different than the code sent to bob.

If this is the case then Alice and Bob know they have an Eve, and can take appropriate steps to remedy the situation.

How it Works Continued

Alice creates a message

It is then converted to Binary

The Key is added to the Binary

Bob subtracts the Key

Then Decrypts the message

Bob reads the message.

Strengths/Benefits

• An encryption method that can detect eavesdropping.• Messages use scrambling during the transaction so they cannot be

identified.• Authentication can be verified between the two parties.• Security of messages is almost completely unbreakable unless the

code (key) being used is already known.• Messages can be uncoded relativly fast after they are sent.

Weakness/Shortcomings

• As computing power increases, and new classical computational techniques are developed, the length of time that a message can be considered secure will decrease, and numerical keys will no longer be able to provide acceptable levels of secure communications.

• If an outside party is able to gain knowledge of the code ebing used then they can send false messages misleading the two parties. 

• Two parties sending messages must have an established reading/coding of how to decipher the codes before messages are sent.

• Cost is high  

Real Life Examples

• (2004) World's first bank transfer using quantum cryptography in Vienna, Austria.

• (2004) DARPA Quantum Cryptographic Network in Massachusetts, USA.

• (March, 2007) BB84 implementation along 148.7 km fibre optic cable in Canary Islands.

• (October, 2007) Quantum Cryptography used in Geneva for swiss elections.

• (October, 2008) Worlds first computer network protected by quantum cryptography implemented in Vienna.

 

Work Cited

"Quantum Cryptography: Privacy Through Uncertainty." CSA. Salvatore Vittorio, Oct. 2002. Web. 09 May 2011. http://www.csa.com/discoveryguides/crypt/overview.php. Goldwater, Sharon. "Quantum Cryptography and Privacy Amplification." Artificial Intelligence Center @ SRI. Web. 09 May 2011. <http://www.ai.sri.com/~goldwate/quantum.html>.

"Short History of Quantum Information Processing."http://www.qipartners.com/publications/Short_History_of_QC.pdf