Secret Key Authentication

• Each individual A and B picks a random number rA and rB which are only known to themselves and a fresh for session to be authenticated. There is shared key KAB which is not to be transmitted but A needs to know that B knows KAB and B needs to know that A knows KAB. The random numbers are known as challenges.

rA

Decrypt xA and see it gives rA

Encrypt rA to give xA

xA

rB

Encrypt rB to give xB

xB

Decrypt xB and see it gives rB

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