Quantum cryptography

QUANTUM CRYPTOGRAPHY

BY:

HIMANSHU SHEKHAR

PRASOON SRIVASTAVA

TRADITIONAL CRYPTOGRAPHY

• The problem with public-key cryptology is that it's based on the staggering size of the numbers created by the combination of the key and the algorithm used to encode the message.

• The problem with Private key algorithm is that there's almost always a place for an unwanted third party to listen in and gain information the users don't want that person to have.

ONE OF THE GREAT CHALLENGES OF CRYPTOLOGY

To Keep Unwanted Parties Or Eavesdroppers From Learning Of Sensitive Information.

And the solution is “QUANTUM CRYPTOLOGY”

QUANTUM CRYPTOLOGY

Quantum physics is a branch of science that deals with discrete, indivisible units of energy called quanta as described by the Quantum Theory. There are five main ideas represented in Quantum Theory:

1. Energy is not continuous, but comes in small but discrete units.

2. The elementary particles behave both like particles and like waves.

3. The movement of these particles is inherently random.

4. It is physically impossible to know both the position and the momentum of a particle at the same time. The more precisely one is known, the less precise the measurement of the other is.

5. The atomic world is nothing like the world we live in.

QUANTUM CRYPTOLOGY BASICS

1.Quantum cryptography uses photons to transmit a key

2. Each type of a photon's spin represents one piece of information -- usually a 1 or a 0, for binary code

3.Polarize them through either the X or the + filters, so that each polarized photon has one of four possible states: (|), (--), (/) or ( ).

QUANTUM CRYPTOLOGY WORKING• Alice sends Bob her photons using an LED, so that each polarized photon

has one of four possible states: (|), (--), (/) or ( ).

• As Bob receives these photons, he decides whether to measure each with either his + or X filter -- he can't use both filters together.

• . After the entire transmission, Bob and Alice have a non-encrypted discussion about the transmission.

• Bob: Plus Alice: Correct

• Bob: Plus Alice: Incorrect

• Bob: X Alice: Correct

• A third party listening in on their conversation can't determine what the actual photon sequence is.

REALIZATATION OF QUANTUM CRYPTOLOGY USING MATLAB

1.Here we will realize our “X” and “+” filter using following table.

“+”table “X” table

2. Filter selection:

a) By LFSR

b) Simple random sequence which will be retained by the sender.

 11

 10

 01

00

 00

 01

 10

11

Our message: “lovely professional university”

Its symbol output: Transmitted Data “Few binary sequence”

Received Data Sequence:

Binary data Sequence

01 10 11 00 01 10 11 11 01 11

Symbol Transmitted

2 0 3 1 0 2 1 1 1 1

Limiter Used + + X X X X + + X +

Received Sequence 2 0 3 1 0 2 1 1 1 1

Predicted Limiter X + + + X X + X + +

Received Symbol  10 10 00 11 01 10 11 00 10 11

Table representing the asking process: Bob Replies for his choice of filter

X + + + X X + X + +

Response W R W W R R R W W R

W- Wrong R- Right

Hence, Bob Gets information about the choice of filter and corrects himself for the wrong one (either discards it and ask for retransmission, or makes a guess).

Knowledge of changed sequence

If the choice of filter used is correct but the data matched for parity is found wrong, then the receiver gets to know that the data sequence has been tampered. Hence, he can stop the transmission further knowing that the communication channel is being tapped.

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