For the following protocol: 1. AS:(B,{(A,KA)}Kpbs) 2. SB:A 3. BS:(A,{(B,KB)}KpbS) 4. SA:(B,{KB}KA) What is KA useful for: 1- Proving A 's identity to B 2. Proving B's identity to A 3. Proving A's identity to S 4- Proving B's identity to A and transporting KB secretly to A 5. Proving A's identity to B and transporting KB secretly to A 6- Proving A's identity to S and transporting KBB secretly to A 7. Transporting KB secretly to A 8- None of the above