Quantum Cryptography. Qingqing Yuan. Outline. No-Cloning Theorem BB84 Cryptography Protocol Quantum Digital Signature. One Time Pad Encryption. Conventional cryptosystem: Alice and Bob share N random bits b 1 …b N Alice encrypt her message m 1 …m N b 1 m 1 ,…,b N m N
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Classical public channel
EveBB84 Protocol (I)
O(N) classical and quantum communication to establish N shared key bits
Public & Classical
Shared KeyBB84 Protocol (II)
Alice’s bit: 1 0 1 0 0 1 1 1 0 1 1 0
Alice’s basis: Diagonal
Alice sends: - + - + + - - - + - - +
Bob’s basis: R D D R D R D R D D R R
Bob’s rect. table: 0 1 0 1 1 1
Bob’s Dia. table: 0 1 0 1 0 1
Bob guess: diagonal
Alice reply: you win
Alice sends original string to verify.