quantum cryptography how could you transmit information safety? thanks to codes
TRANSCRIPT
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Quantum cryptographyHow could you
transmit information safety?
Thanks to codes
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Cryptography is everywhere
Credit card
Military secret
Internet communication (shopping, mails, …)
(…)
The Enigma machine
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Hackers too!!
Every short of information
could be captured
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Contents :
Why ‘quantum’ ?
How does it works?
And the hacker?
Conclusion
What is quantum cryptography ?
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Some rules of quantum mechanic : • every energy variation is quantified (e.g. allows
production of single photon by exciting diamond with laser pulse);
• a measure (every type of measure!) on a system always disrupt it or destruct it (e.g. seeing is absorbing a photon);
• in quantum physic everything is probability, nothing is perfectly predictable.
Why ‘quantum’ ?
Looking a cylinder is like observing a quantum object.
Where is this electron? (simulation)
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How does it works ?
A is sending to B a sequence of some thousand random bits coded on single photons by random polarization
BA
Polarization bases convention (‘code’ convention): circular (C) or linear (L)
1 0 1 0
LC RC V H
Key code
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B detection
B randomize the polarization base to detect each photon and attribute a value to the bit thanks to the ‘code’ convention.
BA
User Sequence
Bits A 0 1 1 0 0 1 1 0 1 Random key
Polarization A C C L C L C C L L Random basesB L L L C C C C L C
Bits B 1 1 1 0 1 1 0 0 0 Rough key
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User Sequence
Bits A 0 1 1 0 0 1 1 0 1 Random key
Polarization A C C L C L C C L L Random basesB L L L C C C C L C
Bits B 1 1 1 0 1 1 0 0 0 Rough key
User Sequence
Bits A 0 1 1 0 0 1 1 0 1 Random key
Polarization A C C L C L C C L L Random basesB L L L C C C C L C
Bits B 1 1 1 0 1 1 0 0 0 Rough key
Measure errors detection and correction
After transmission it subsists mistakes User Sequence
Bits A 0 1 1 0 0 1 1 0 1 Random key
Polarization A C C L C L C C L L Random basesB L L L C C C C L C
Bits B 1 1 1 0 1 1 0 0 0 Rough key
User Sequence
Bits A 0 1 1 0 0 1 1 0 1 Random key
Polarization A C C L C L C C L L Random basesB L L L C C C C L C
Bits B 1 1 1 0 1 1 0 0 0 Rough key
A and B compare their base choices sequence using a classical network and eliminate mistakes : reconciliation step.
User Sequence
Bits A 1 0 1 1 0 Filtered key
Polarization A L C C C L SamebasesB L C C C L
Bits B 1 0 1 0 0 Filtered key
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Transmission errors detection and correction
A and B sacrifice a part of their filtered key to evaluate the transmission error ratio due to physical causes or to a hacker (or more!).
User Sequence
Bits A 1 0 1 1 0 Filtered key
Polarization A L C C C L SamebasesB L C C C L
Bits B 1 0 1 0 0 Filtered key
1
C
C
0
0
C
C
0
Ok ERROR
Confirmation step : if too much errors => start the process again
Exchanged part
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Last step : KEY CONSTRUCTION
A and B use separately corrective algorithms to correct transmission errors and to amplify the confidentiality thanks to jamming the key .After that : only ONE key for A and B but WITHOUT TRANSMISSION of this one!
Users Keys
A 1 1 0 The same
keysB 1 1 0
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And the hacker ?
BA
The hacker could make many things…SO MANY!!....
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The hacker could take information during transmissions. He could :
During the first exchange :
• steal some photons during the first exchange;• and/or (re)emit photons to mistake B;
During the reconciliation step :
• read all the base choices of A and B;
During the confirmation step :
• read all the sacrificed sequence;
Hacker’s actions have manyconsequences :
• he must detect photons as the same way as B => he makes errors;• he introduces more errors;• he cannot control error rate;
• he haven't necessarily the same choices => he loses information whereas A and B no;
• he can’t do anything from this time!
…BUT there is a price!!!
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To get enough information, the hacker had introduced a non-negligible amount of errors and so he will be detected and…
EVERYTHING WILL RESTART!!!
And it’s even worst!!!
And so, hacker is THE great looser!
??
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Quantum cryptography is a good solution
Allows secure communication against hackers because
everything is transmitted before creating the key.
Whatever the hacker want to do is against him.
Thanks for your attention