Question

. The following is a key exchange protocol used by two clients, A and B, to obtain a symmetric key???, using a trusted server, S. Assume that A and B had previously obtained the symmetric keys ??? and ??? securely with the server. Also assume that anyone can securely obtain a secret symmetric key with the server. I. A → S : A, B II. S → A : (???) ??? ,( ???) ??? III. A → B : (???) ??? , A • Identify the attack that can be executed against this protocol, assuming that an attacker C can eavesdrop, block, or modify all messages. The attacker also has access to old (expired) keys.

Note: Show me the answer with mathematical way and explanation

Answer 1

1). ANSWER :

GIVENTHAT :

As Per above Problem, Client A and B are trying to communicate using symmetrickey exchange protocol.

Example for SysmmetricKey Exchange Algorithm is...AES, DES , Blowfish, RC4,, RC5, and RC6 etc.

Here, Problem with the above question is that Attacker C knows......Old(expired) keys and he can eavesdrop, block or modify all messages.

So Based on That below are possible attacks can happen.

1. Brute force attacks ->> In this Attack on an encrypted message is simply try to attempt to decrypt the message with every possible key. If One key not works then other key willl try and so on. This is not a very efficient technique.

2. Replay attack -->> It can happen when hacker eavesdrops on a secure network communication, intercepts it and then fraudulently resends it to misdirect the receiver into doing what the attacker wants.

3. Phishing attacks --> when attacker have acccess to messages.

4. Cryptanalysis --> when attacker knows plaintext and can modify it.