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Quantum Cryptography

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Cryptography.

Transmitting information with access restricted to the intended recipient even if the message is intercepted by others.

Cryptography is of increasing importance
in our technological age using broadcast, network communications, Internet ,e-mail,
cell phones which may transmit sensitive information related to finances, politics,
business and private confidential matters.

PKC :the modern cryptography

In 1970s the Public Key Cryptography emerged.
Each user has two mutually inverse keys,
The encryption key is published;
The decryption key is kept secret.
Anybody can send a message to Bob
but only Bob can read it.

Elements of the Quantum Theory

Light waves are propagated as discrete quanta called photons.
They are massless and have energy, momentum and angular momentum called spin.
Spin carries the polarization.
If on its way we put a polarization filter
a photon may pass through it or may not.
We can use a detector to check of a photon has passed through a filter.

Heisenberg Uncertainty Principle

Certain pairs of physical properties are related in such a way that measuring one property prevents the observer from knowing the value of the other.
When measuring the polarization of a photon, the choice of what direction to measure affects all subsequent measurements.
If a photon passes through a vertical filter
it will have the vertical orientation regardless of its initial direction of polarization.

Quantum Cryptography


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What is Cryptography?


Art of encrypting and decrypting the messages to transmit the information such that only intended recipient receives it.

Encryption and Decryption uses KEY.

The key has to be shared between sender and receiver for the secure transmission.

But how the key is shared? Can the key be hacked while it is being transmitted through the channel?


Classical Cryptography


There are 2 methods in classical cryptography-
Symmetric cryptography.
Asymmetric cryptography.


In both cases eavesdropper can not deduce the information without knowing the key.


Limitations of Public-key encryption

This method involves advanced number theory.

The pair of keys are mathematically related .

Trying to determine one key from the other involves solving a problem that is mathematically “hard.” This makes the RSA method difficult to crack like Discrete algorithm problem.


Principles Of Quantum Cryptography


Instead of bits 0 and 1,the photon corresponding to those bits are passed through secure channel called Quantum channel.

These bits are called Qu-bits.

The properties of Quantum Physics which make the communication secure are-

1. Polarization.
2. Heisenberg's uncertainty principle.
3. Quantum Entanglement.
4. No Cloning Theorem.


Conclusion

If the huge processing power of futuristic quantum computers can be implemented, then most public key cryptography will become history.

The ultimate goal is to make QKD more reliable, integrate it with today's telecommunications infrastructure, and increase the transmission distance and rate of key generation.

Quantum cryptography already provides the most advanced technology of quantum information science, and is on the way to achieve quantum jump from university laboratories to the real world.

QUANTUM CRYPTOGRAPHTY

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CRYPTOGRAPHY

Cryptography is the process of converting ordinary information called plaintext into unintelligible gibberish called cipher text
Decryption is the reverse, in other words, moving from the unintelligible cipher text back to plaintext.
The detailed operation of a cryptography is controlled both by the algorithm and in each instance by a "key".

QUANTUM MECHANICS

Spawned during the last century
Branch of physics that Describes properties and interaction between matter
Quantum state of a system is determined by
Positions
Velocities
Polarizations
Spin
Qubits - quantum bit is a unit of quantum information
Quantum states are used to represent binary digits 0 and 1.
One could for example use the spin of a particle and let UP-spin to be zero and DOWN-spin to be one and vice versa.

Existing cryptographic methods

Existing cryptographic methods include the
Public key cryptography and the private key cryptography
The existing cryptography methods use algorithm and mathematical calculations to generate the key
Transmission of data via classical channel

DRAWBACKS

Existing key distribution methods are vulnerable to impersonation
Cannot detect the presence of an intruder
Noisy channels may disrupt the transmission
The size of the key is very large
These keys can be easily decoded using mathematical formulas or using a Quantum computer

Overview of Quantum cryptography

Quantum cryptography is based on the principle of Quantum mechanics
The Quantum cryptography uses QUBITS to transmit the data over a optic fiber channel
The data that has to be transmitted is sent as a photon this photon is called as a QUBIT
Quantum cryptography can detect the presence of a intruder trying to intercept the information
Quantum cryptography uses BB84 protocol

Key distribution – BB84

The key distribution takes place over a Quantum channel and a Classic channel
sender prepares photons randomly with either rectilinear or circular polarizations and sends it
receiver receives each photon and randomly measures its polarization according to the
rectilinear or circular basis.
He records the measurement type (basis used) and the resulting polarization measured.
The polarization sent by sender may not be the same polarization receiver finds if he does not use the same basis as sender.
receiver publicly tells sender what the measurement types were, but not the results of the measurements.
sender publicly tells receiver which measurements were of the correct type.
sender and receiver each throw out the data from measurements that were not of the correct type

Conclusion

Information can be transmitted securely
Even if a intruder tries to eves drop the qubits there is a high possibility of not cracking the information
The ability to detect eavesdropping ensures secure exchange of the key
Equipment can only be used over short distances
Equipment is complex and expensive