There are three typical ways to use nonces as challenges. Suppose Na is a nonce generated by and B share key K, and f0 is a function (such as an increment). The three usages are Usage 2 B>A: E(K, Na (2)B>A: Na 2)B>A: E(K,fNa) Usage 1 Usage 3 (I)AB: Na (2 Describe the possible attack for each usage (IAB: E(K, Na)AB: E(K, Na)