Reference no: EM133424202
Question 1
In class we learned a fundamental set of cryptography systems. For the duration of these questions presume you have access to a small, but trusted source of information (i.e., a public website).
Discuss how you would apply them to the following situations:
1. Someone who has never communicated with you in the past needs to send you a secret message over an insecure channel. How can he create it so that only you can read it?
2. You need to receive orders over an insecure channel from your boss. How can you make sure his message's integrity has been preserved?
Question 2 What is the difference between a message authentication code and a one-way hash function?
Question 3 List possible ways to distribute secret keys to two communicating parties.
Question 4 List four general categories of schemes for the distribution of public keys.
Question 5 What is a public key certificate?
Question 6 Consider a Diffie-Hellman scheme with a common prime q=11, and a primitive root g=2.
(1) Show that 2 is a primitive root of 11.
(2) If user A has public key Ya=9, what is A's private key Xa?
(3) If user B has public key Yb=3, what is the shared secret key K, shared with A?
Question 7 (1) Consider the Davies and Price hash code scheme described in Section 11.4 and assume that DES is used as the encryption algorithm:
Hi = EMi[Hi-1] Å Hi-1
And recall the complementarity property of DES: If Y = DESK(X), then Y' = DESK'(X'). Use this property to show how a message consisting of blocks M1, M2, ..., MN can be altered without altering its hash code.
(2) Show that a similar attack will succeed against the scheme proposed in [MEYE88]:
Hi = EHi-1[Mi] ÅMi