Quantum Cryptography

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Quantum Cryptography
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Cryptography

• Art of writing messages so that no one other than
  intended receiver can read it.
• Encryption Performing mathematical operations
  to hide message content.
• Decryption Reverse of encryption to get
  original message
• Plain Text A clear unencrypted message.
• Cipher An Algorithm to encrypt plain text and
  convert it into seemingly nonsensical cipher
  text.
• Cipher Text The finally encrypted text

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Some Well known Methods

• Public Key and Private Key Systems Uses a
  Public Key to encrypt and Private key is used to
  decrypt message.
• One Time Pad(OTP) The OTP is the random key ,
  same length as message, applied once and only
  once. Theoretically IMPOSSIBLE to decipher the
  message without the key.
• Some Other methods are RSA, DES, Double DES ,
  Triple DES, Digital Signatures etc.

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Quantum Computing

• Superfast Computing. Based on the principles of
  Quantum Theory .
• Photons will be the data carriers.
• Building Blocks are QUBITS. A QUBIT can be 0 or
  1 at the same time.
• Operations are performed on QUBITS and their
  properties.
• Can factorize 250 digit number in finite time.
• Finding Key of is just a matter of time.
• Present encryption techniques will become
  useless.

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Important facts

• The properties of photons are tied together so
  tightly that measuring one property will cause
  change in other thus disturbing the whole system
• In Quantum World A particle can be in any state
  until it is observed. Once observed It gets
  settled in that state.
• The concept of uncertainty states that One
  cannot have the knowledge about two properties
  of a photon at the same time . For example
  Heisenberg uncertainty principle.

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• The concept of Quantum Entanglement states that
  photons are so closely related that it is
  impossible to describe One without another.
• An attempt to measure the property of one photon
  will immediately Affect the other Photon.
• It is like One Photon talking to Another photon
  in no time.

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Quantum Cryptography

• The property of photons used in Quantum
  Cryptography is Polarization .
• Light Waves moves in every plane.
• Polarization is the act of selecting light waves
  of a particular plane.
• In Linear polarization Light can be polarized
  either horizontally or vertically.
• In circular polarization light waves are made to
  move in circular fashion.

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• Linear and circular polarization are bound with
  uncertainty .
• Measurement of linear polarization will destroy
  measurement of circular polarization.

1. Light travels in all planes. 2. Horizontal
Polarisationisolating
light that travels horizontally 3.
Vertical Polarisation 4. Circular
polarisation
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Artur Ekerts Card Trick

• Given by Artur Ekert in 1991 to explain quantum
  cryptography.
• There is a whole bunch of sealed envelops with
  red and blue cards, marked with 0 and 1, in them.
• two machines to read the cards. Red and blue
  machine.
• Red machine understands red card and blue machine
  understands blue card.
• Red card with 1,in red machine will output 1.
• Similarly for Blue cards with blue machine.
• If Red card with 0 is inserted in blue machine ,
  it will throw a random guess of 0 or 1.

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• Let us say there are two people Alice and Bob who
  want s to share the secret key safely.
• We hand over one sealed envelop to each.
• They will get the same results if they use the
  same color machine.
• This happens due to the concept of quantum
  entanglement.
• When Alices blue machine says the card is blue
  and 1 written on it, then both the cards are
  blue. And so blue machine of Bob will process the
  card as blue and yield the same result.
• For sharing key they only tell each other what
  machine they used for every card and not the
  card.

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• Due to Quantum Entanglement they will get same
  result every time they use same machine.
• To verify they will tally some of the values.
• The tally values and different machine values are
  discarded.
• The remaining left is the KEY.

The measurements that Alice (top row) and Bob
(bottom row) make. They get the same result when
they make the same measurement.
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Now that theyve made their measurements, they
only keep the results where they both used the
same machine
They pick random results and compare them to see
if there were errors
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Finally, the Key!
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Final Words

• The Concept of quantum cryptography has been
  around since the 1970s .
• Working models have been set up in educational
  institutes.
• Can be implemented on fiber optics Network, which
  is not very common.
• Infrastructure for quantum cryptography system is
  Expensive.
• Companies like New Yorks MagiQ and Genevas
  idQuantique are already providing quantum
  cryptography solutions to banks and military.

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Thank You