The Challenge - Handshake Authentication Protocol ( CHAP ) is used primary for what?
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Akash M.
22. Consider the following mutual authentication and key establishment protocol, where the session key is given by K = gab mod p. "I'm Alice", RA Rg, [RA1Bobs{gb mod p}Alice [Rg]Alice, {ga mod p}Bob Alice Bob Suppose that Alice attempts to initiate a connection with Bob using this protocol. a. Show that Trudy can attack the protocol so that both of the following will occur: i. Alice and Bob authenticate each other. ii. Trudy knows Alice's session key. Hint: Consider a man-in-the-middle attack. b. Is this attack of any use to Trudy?
4. Key agreement/IKE (10-5-10 points): (a) Consider the following key exchange protocol which is similar to IKE Phase 1 Aggressive Mode. p is a large prime number and g is a generator of Z*p. 1. A → B : g^a mod p, {"Alice"}Bob, {RA}Bob 2. A ← B : g^b mod p, {"Bob"}Alice, {RB}Alice, proofB 3. A → B : proofA where proofA = h(g^ab mod p, g^a mod p, g^b mod p, "Alice") proofB = h(g^ab mod p, g^b mod p, g^a mod p, "Bob") K = h(g^ab mod p) i) First explain if the protocol authenticates A and B, and achieves secure key agreement (discuss key control and key authentication). {m}x denotes a message m encrypted with public key of x. ii) Modify the protocol so that RA and RB can be eliminated but the protocol can mutually authenticate A and B. In your modification, no additional protocol message, secret keys or signature can be used. (b) Consider the following simplified IKE Phase 1 in Aggressive Mode. A → B : "Alice", "Bob", g^a mod p A ← B : "Bob", "Alice", g^b mod p, [g^a mod p]B A → B : "Alice", "Bob", [g^b mod p, g^a mod p]A [X]A denotes a signature on message X generated by A. The session key established between A and B is g^ab mod p. Show that this simplified version is insecure (allows attacker to establish a key with one of the participants while pretending to be the other participant). Hint: consider that this IPSec system has multiple users.
Sri K.
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