Zero-Knowledge Proof Framework: A Interactive Authentication Method, Lecture notes of Computer Security

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CSIS 0327

Computer & Network Security

Extra Zero Knowledge Proof Note

Dr Lucas Hui

(CYC307, 28592190, [email protected])

2

A Zero-Knowledge Interactive Proof Framework

• a query Q, with secret A is the answer
• Repeat n time (say n=10)
  • Peggy (the user who wants to authenticate) creates a transformation

on A, so A is presented as two parts: A1 and A2 (If both A1 and A

are given out, the A can be re-constructed)

• with 1/2 probability, Venus asks Peggy to disclose
  • A1, or
  • A
• P creates a new pair of A1, A2 every time
• If P does not know A, P can either create a faked A1, or a faked A

P V (system)

(user) T( )

The choice (A1 or A2)

A1 or A

• Secret: position of a small pattern in a big picture
• Prover: Peggy
• Verifier: Venus Example : Where is Waldos?

How Peggy prepare for giving the ‘answer’ Use a big “cloth” After the preparation, Venus will ask for A1 or A

Sep 2015 The 2 ‘half solutions’ (1) A1 : Review the answer (i.e. the figure) A2 : Take off the big cloth A1 : Review the answer (the figure)

The 2 ‘half solutions’ (2) A1 : Review the answer (the figure) A2: Take off the big cloth A2 : Take off the big cloth

Sep 2015 How Peggy cheats for ‘half solution’ (1) A1 : Review the answer (the figure) A2 : Take off the big cloth Peggy gets the above figure, hope that Venus will ask for : A1 : Review the answer (the figure)

How Peggy cheats for ‘half solution’ (2) A1 : Review the answer (the figure) A2 : Take off the big cloth Peggy just put the original figure under cover, hope that Venus will ass for: A2 : Take off the big cloth