CPSC 42500 Kings College Diffie Hellman Key Exchange Discussion

Here are the topics and they are a few questions about addendum: Diffie-Hellman Key Exchange

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CPSC 42500 Homework 7 addendum: Diffie-Hellman Key
Exchange
1. (2 pts) Give two different ways to simplify the expression (32)4 and show that they are equal.
2. Pretend you are Alice and have agreed with Bob to carry out Diffie-Hellman key exchange
with parameters p = 23 and g = 5. You may use a calculator to answer the following, but
write down and label all the quantities you use.
a. (2 pts) Assume you choose the secret random value x = 19. Compute the value gx (mod p)
that you will send to Bob.
b. (2 pts) In the protocol, you receive the value gy = 18 from Bob. Compute your shared
secret value.
c. (4 pts) Now pretend you are an eavesdropping adversary. From g, p and gy, find Bob’s
secret y (it’s possible!)
d. (4 pts) Describe how you found the value in part (c), and comment on how this reflects
the security of Diffie-Hellman key exchange.
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