Single Photon Quantum Single Photon Quantum EncryptionEncryption

Rob GroveRob GroveApril 25, 2005April 25, 2005

Background

Current Encryption

Quantum Mechanics

Quantum Encryption

Limitations

Predictions

• Telephone

• Internet

• Courier

• In person

Bob needs to get a secure message to Alice

Background

Current Encryption

Quantum Mechanics

Quantum Encryption

Limitations

Predictions

Private Key

Private Key Private Key CryptographyCryptography

Bob Alice

Eve

• Private key encryption uses permutations and other reversible mathematical operations to encode the message.

Private Key Encrypt/DecryptPrivate Key Encrypt/Decrypt

Background

Current Encryption

Quantum Mechanics

Quantum Encryption

Limitations

Predictions

Public Key Public Key CryptographyCryptography

Bob Alice

Eve

Public Key

Encrypted Message

Public Key EncryptPrivate Key Decrypt

• Public key encryption uses prime multiplication and other very hard to reverse mathematical operations to encode the message.

Background

Current Encryption

Quantum Mechanics

Quantum Encryption

Limitations

Predictions

1.1. In conventional data transmission every bit In conventional data transmission every bit has a definite value of 0 or 1.has a definite value of 0 or 1.

2.2. Linearly polarized atomic particles can be Linearly polarized atomic particles can be used as data bits for quantum data used as data bits for quantum data transmission.transmission.

3.3. Qubits can change their state when Qubits can change their state when measured.measured.

4.4. Linear polarized photons are natural Linear polarized photons are natural qubits.qubits.

5.5. Qubits are extremely delicate.Qubits are extremely delicate.

Quantum bits (Qubits)Quantum bits (Qubits)

Background

Current Encryption

Quantum Mechanics

Quantum Encryption

Limitations

Predictions

Polarization of PhotonsPolarization of Photons

-1-0.500.51

-1

0

1

0

20

40

60

80

100 Polarization

-1-0.5

00.5

1

-1

0

1

0

20

40

60

80

100

Polarization

Background

Current Encryption

Quantum Mechanics

Quantum Encryption

Limitations

Predictions

Wave PolarizationWave PolarizationCircular Polarization

Linear Polarization

Background

Current Encryption

Quantum Mechanics

Quantum Encryption

Limitations

Predictions

Polarizing Polarizing FiltersFilters

Filters can be used Filters can be used to measure photon to measure photon polarizationpolarization

Polarized at 45 degrees

Filters can be used Filters can be used to polarize photons to polarize photons into qubits for data into qubits for data transmissiontransmission

Background

Alice’s Receiving Filters

Key 1 11 1Current Encryption

Quantum Mechanics

Quantum Encryption

Limitations Predictions

Bob’s Values 0 1 1 1 0 1 1 0

Alice’s Measured Values 1 1 1 1 1 1 1 0

Encryption ExampleEncryption Example

Bob’s Sending Filters

0 10

1

Bob Confirms Correct Filters

Background

Current Encryption

Quantum Mechanics

Quantum Encryption

Limitations

Predictions

MethodMethod

Bob

Alice

1. Bob generates two random number sequences.

Bob’s Filter100101010001 010111100111

Alice’s Filter110011000100

2. Alice generates one random sequence and uses it to filter Bob’s data.

3. Alice tells Bob her filter sequence and Bob tells her which ones are wrong.

Subset of Bob’s Key

Background

Current Encryption

Quantum Mechanics

Quantum Encryption

Limitations

Predictions

Introduces gross error > 25%

Quantum EncryptionQuantum EncryptionBob Alice

Eve

Key

Background

Current Encryption

Quantum Mechanics

Quantum Encryption

Limitations

Predictions

Shannon’s Secure Cryptography Shannon’s Secure Cryptography EquationEquation

0)|()();( MCHCHCMI

entropy is

tcipher tex theis

message theis

ninformatio is

H

C

M

IThe only way this can happen is if a totally random key of equal length to the message is XOR’d with the message.

Background

Current Encryption

Quantum Mechanics

Quantum Encryption

Limitations

Predictions

Quantum Encryption ProblemsQuantum Encryption Problems

• Restricted to fiber-optics cable

• Greatest distance proven is under 62 miles

• Hardware is expensive

• Individual photons have not been demonstrated

• Data throughput is not very high, 1~10 kb / s

Background

Current Encryption

Quantum Mechanics

Quantum Encryption

Limitations

Predictions

Specific Application EncryptionSpecific Application Encryption

• Will not be a substitute for public key encryption for most applications

• Will not directly impact 99% of internet users

• Will be a useful tool against massive internet attacks on back bone structure

• Will be a solution for line of sight business encryption

Background

Current Encryption

Quantum Mechanics

Quantum Encryption

Limitations

Predictions

ReferencesReferences• http://www.wsi.tum.de/E24/research/spintronics/spintronics.htm

• http://www.mycrypto.net/encryption/crypto_algorithms.html

• http://www.tryagain.com/humcivil/qntmencr.htm

• http://www.idquantique.com/files/introduction.pdf

• http://www.cs.jhu.edu/~scheideler/courses/600.471_S03/lecture_6.pdf

• http://www.cs.dartmouth.edu/~jford/crypto.html

• http://www-theory.chem.washington.edu/~trstedl/quantum/quantum.html

• http://scienceworld.wolfram.com/physics/WaveEquation.html

• http://www.wordless.com/CGI/article.asp?ArticleId=21

• http://www.mtnmath.com/whatrh/node78.html

• http://www.th.physik.uni-frankfurt.de/~jr/physpicquant.html

• http://www.trnmag.com/Stories/2002/112702/Fast_quantum_crypto_demoed_112702.html