Quantum Cryptography By : Davis Polus

1
Quantum CryptographyBy Davis Polus
Photon light
2
What is Quantum Cryptography?

• Quantum cryptography uses a cryptographic
  technique based on the physics of light, not
  mathematics.
• Quantum cryptography involves natural occurrences
  of values found in light in achieving
  unconditional security, also called perfect
  security.

Here, quantum information is stored in localized
states of light. Quantum computers can perform
calculations in relatively short "polynomial
time". These calculations require very long
"exponential time" with any classical computer
also called digital computers
3
3 Methods used to approach quantum cryptography
?1. photon polarization 2. quantum
key distribution 3. quantum computing
2.
1.
3.
4
Photon Polarization

• Photon polarization is the quantum mechanical
  description of the classical polarized sinusoidal
  (wave,curves) plane electromagnetic wave.
• Each photon individually is completely polarized.
  
• PolarizedTo separate or accumulate positive and
  negative electric charges in two distinct
  regions.
• Each photon carries one bit of quantum
  information.
• In order to receive the one bit, the receiver has
  to know the photons polarization.
• The state of polarization can be oval, circular,
  or linear.
• Unitary operators come from the classical
  requirement of energy conservation of classical
  wave spread through media that changes the
  polarization state of the wave.

5
Photon Polarization And Eavesdrops Prevention
Eavesdropping in terms of quantum information can
be seen as a measurement on a physical object or
the carrier of the information.
6
Quantum Key Distribution

• Public key cryptography is needed for factoring
  large numbers
• Factoring is defenseless to attack from quantum
  computers
• Instead of depending on the relative strength of
  a mathematical problem, QKD uses principles of
  quantum mechanics to guarantee the
  confidentiality and integrity of data.
• The key standard behind this technique is the
  Heisenberg Uncertainty principle, one of the
  fundamental results of quantum physics
• According to this law, in order to observe
  certain information about a particle, an observer
  loses the ability to know other data. Basically,
  certain classes of information about a particle
  are together exclusive

7
Quantum Key Distribution cont..

• Many different types of quantum key distribution
  have been researched, but the most well known of
  these is the BB84 protocol, which uses polarized
  light sent down a fiber optic cable
• Since different angles of polarized light form
  two sets of coupled pairs which are rectilinear,
  or a and 9a degrees, and diagonal, or 45 and 135
  degrees, single photons are sent down the fiber
  and observed by the receiver
• Since the receiver has no way to know if his or
  her observation of the photon used the correct
  angle, he or she checks on a public channel with
  the sender if the choice of rectilinear or
  diagonal was correct
• An attacker will gain no information from this
  check and, in addition, will alert both the
  sender and receiver to his or her presence with
  an increase in error rates

8
How Are Keys Used In Quantum Cryptography?

• For creation of messages, a combination of
  quantum and classical techniques are used to
  create a key, which is proven to be secure . In
  other words, a hidden key cant be read by
  anybody but the person who created it.

The sender Alice, sends a string of bits,
choosing randomly to send photons in either the
rectilinear or the diagonal modes. The receiver,
known as Bob makes a similarly random decision
about which mode to measure the incoming
bits. After transmission, Bob then communicates
with Alice, an exchange that need not remain
secret, to tell her which of the two modes he
used to receive each photon.
9
Quantum Computing

• Cryptography relies on certain mathematical
  problems being easy for the good people and very
  difficult for the bad people
• For example, in public key cryptography, the good
  people only have to compute a random exponent
  from large numbers, a very good problem
• The bad people, however, have to factor random
  numbers
• Quantum computers hold the promise for the fact
  of lowering the difficulty of many problems
  underlying cryptography
• Through properties such as superposition and
  complication, quantum computers can execute
  search and factor algorithms many orders of
  magnitude faster than current classical computers
  

10
Quantum Computing Cont

• Quantum computing works because the laws
  governing microscopic particles are not anything
  like the macroscopic world we are used to
• According to quantum mechanics, however, for
  example a dog is both alive and dead until an
  observer opens the box.
• An electron can either be spin up or spin down
• However, unlike macroscopic particles, the
  electron can also be both spin up and down at the
  same time, a state known as quantum superposition
  
• Humans observe objects by monitoring the light
  bouncing off them

11
Quantum Computing Cont

• Small systems like the spin of an electron
  represent the smallest amount of information a
  quantum computer can hold, a qubit (for quantum
  bit)
• Qubits are similar to normal bits in a classical
  computer, in that when observed they output
  either a one or a zero
• However, unlike classical bits, qubits actually
  contain more information that is not directly
  observable, the so-called hidden variables
• To run an algorithm on a quantum computer, a
  programmer must control an array of qubits
  through a series of transformations and then
  observe the end result
• Faster search attacks decrease the amount of time
  needed for dictionary cracking attacks on hashes
  and secret key cryptography
• However, only the factoring algorithm represents
  a major threat with its exponential decrease in
  time
• Secret key systems will remain safe as long as
  key sizes are doubled.

12
Class Question
Quantum computers can perform calculations in
relatively short
polynomial time.
_____________