Description

“Message authentication is one of the key requirements of a secured cryptosystem. The question concerns message authentication and Diffie- Hellman key exchange.”

“Describe your understanding of message authentication and the methods used to achieve it. (6 marks)”

Consider the following key agreement protocol:
A→B: gx mod p.
B→A: gy mod p, EK(SB(gy mod p, gx mod p)).
A→B: EK (SA(gx mod p, gy mod p)).
Assume the following:
A and B agreed on a (g, p) pair for Diffie -Hellman key exchange.
A and B have RSA keys for digital signatures.
A and B agreed on a block cipher E for use in subsequent Encryption.
K is the agreed secret key.
SA and SB denote A’s and B’s signature operations.”

“Describe in detail A’s and B’s actions at the receipt of messages 2 and 3 and their belief at that stage. (7 marks).”