Secret Handshakes

CREATED: 200712180732 Speaker: Xu Shouhai, University of Texas at San Antonio ** Secret Handshake

• A can authenticate B iff B can authenticate A
• minimize exchange of information, privacy preserving authentications ** Approaches
• one time credentials - unlinkability
• special credentials (group signatures) - unlinkability with reusable credentials
• PKI-like infrastructures (no anonymity assurance) - unlinkability with reusable credentials ** Properties of Secret Handshake
• correctness: if u and v belong to the same group, then the handshake succeeds, otherwise the handshake fails
• resistance to impersonation attacks
• k-anonymity: in one of k groups out of n groups ** Construction for k-anonymity (k = 3) using public key infrastructure

A: pick k - 1 other public k

A: send k certs to B

B: encrypt r_1, r_2, …, r_k random strings with each public key, pick k - 1 other public keys, send both to A

A: can only decrypt one of the random strings encrypted by B, encrypt s_1, s_2, .., s_k from the keys sent by B and send these encrypted messages to B

B: can only decrypt one of the random strings

Both: A and B can communicate using the two random strings

** Future work

• secret handshake is a form of secure computation
• minimal complexity
• relationship to covert computation