Quantum Cryptography

QUANTUM CRYPTOGRAPHY

&QUANTUM KEY DISTRIBUTION

What Is Cryptography

Secret message

Importance & Applications

Bob Alice

Eavesdropper

Some keywords

Encryption

Decryption

Encryption Key

Decryption Key

Plaintext

Parts, Embodied In Cryptography

To setup a useful cryptography system, the most important issues you would encounter is the security.

Troubles With Cryptography

Breaking The LOCK

Stealing the information within Key’s exchanging

Quantum Mechanic Parameters

SU

P

E

R

P

OS

I

T

I

O

N Probabilistic

PO

L

A

R

IZ

A

T

I

O

N

POLARIZATION

A simple example of superposition

α

In Classic in the simplest state

0 1

up down

openclose OR

OR

OR

0 , open

1 , close

So what is the difference between the classical superposition and quantum superposition

αAfter

measurement OR

With probability of

With probability of

Classical CryptographyVs.

Quantum Cryptography

DONE.

Classical CryptographyVs.

Quantum CryptographyS

U

P

E

R

P

OS

I

T

I

O

NS

U

P

E

R

POS

I

T

I

O

N

S UP

E

R

POS

I

T

I

ON

S UP

E

R

POS

I

T

I

ON

S UPER

POS

ITIO

N

S UPER

POSITIO

N

SU

P

E

R

P

OS

I

T

I

O

N

I’m Confused

A Simple Quantum Key DistributionProtocol

Charles H.BennetGilles Brassard

1984

BB84

Quantum Cryptography: Public Key Distribution and Coin TossingPublished in physical review

A Byte of message

11001110

KEY Cipher text

A SIMPLE SAMPLE OF KEY AND ITS FUNCTION

Summation rule1+1=01+0=10+0=00+1=1

Quantum bit

α

Polarization of a single photon

Transmition probability

Absorptionprobability

Filter apparatus

|0>

|1>

R ≡ Rectilinear Base

D ≡Diagonal Base

R

R

D D

|1>

|0>

|-> |+>

Translating Quantum Bits Into Classic Bits

0

1

Polarization BasesAnd Quantum Bits

Classical Bits

0

1|0>

|+>|->

|1>

R |0> 0

R |1> 1

D |+> 0

D |-> 1

Bob chooses a random bit string and a random

sequence of polarization bases

(mix of Rectilinear and Diagonal)

Alice receives the photons and decides randomly for

each photon, independently of Bob, whether to measure the polarization of photon in Rectilinear or Diagonal bases

0

1

If absorbed 1If transmitted 0

If absorbed 0If transmitted 1

Will absorbed 0If absorbed

If transmitted

0

1

Will transmitted

1If absorbed

If transmitted

0

1

Quantum transmission 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Bob's random bit 0 1 1 0 1 1 0 0 1 0 1 1 0 0 1

Bob's random bases D R D R R R R R D D R D D D R

Bob's Polarization

Alice random bases R D D R R D D R D R D D D D R

Received bits by Alice 1 1 1 0 0 0 1 1 1 0 1

Public Discussion

Alice reports bases of received bases R D R D D R R D D D R

Bob says which bases were correct OK OK OK OK OK OK

Presumably shared information 1 1 0 1 0 1

Alice reveals some key bits at random 1 0

Bob confirms them OK OK

Outcome

Remaining shared information 1 0 1 1

This information are secure with extremely high probability

So this information are suitable for KEY ; As the result the

KEY has Shared securely

Remaining shared information 1 0 1 1

1 0 1 1

OUTCOME

Conclusion

The protocol is high secure and prevents Information from being Stolen and Hacked by EAVESDROPPER.

Although this protocol is theoretical, it’s not such out of reach to remain in just theories.

Although this protocol is secure enough but cannot prevent from being suppressed and excessively perturbed by EAVESDROPPER or INTRUDER.