Problem 1
Consider the principle of complete mediation. Which non-functional system requirement will likely be affected by adhering strictly to this principle?
Problem 4
What is an algorithmic complexity DoS attack?
Problem 5
Alice wants to communicate with the www.vunl Web site, but the entry for this domain in her name server was poisoned so that the packets end up at an attacker-controlled machine. To what extent is the attacker able to compromise Confidentiality, Integrity, and Authenticity in the following cases: (a) unencrypted (http) communication between Alice and www.vu.nl, (b) encrypted (https) communication between Alice and www.vu.nl when the Web site uses a self-signed certificate, (c) encrypted (https) communication between Alice and www.vu nl when the Web site uses a certificate signed by a legitimate certificate authority?
Problem 6
A stateless firewall blocks TCP connection initiation requests from an external location to any local host. Explain why this defense is not very effective against sophisticated attackers.
Problem 9
Break the following monoalphabetic substitution cipher. The plaintext, consisting of letters only, is an excerpt from a poem by Lewis Carroll. mvyy bek mnyx n yvijyr snijrh invq n muvjvdt je n idnvy jurhri n fehfevir pyeir oruvdq ki ndq uri jhrnqvdt ed zb jnvy Irr uem rntrhyb jur yeoijrhi ndq jur jkhjyri nyy nqlndpr Jurb nhr mnvjvdt ed jur iuvdtyr mvyy bek pezr ndq wevd jur qndpr mvyy bek, medj bek, mvyy bek, medj bek, mvyy bek wevd jur qndpr mvyy bek, medj bek, mvyy bek, medj bek, medj bek wevd jur qndpr
Problem 11
Break the following columnar transposition cipher. The plaintext is taken from a popular computer networks textbook, so "connected"' is a probable word. The plaintext consists entirely of letters (no spaces). The ciphertext is broken up into blocks of four characters for readability. oeet nott rece rowp sabe ndea oana tmrs otne heth imnc trdi ccfa Ixgo ioua iere iybe nft
Problem 12
Alice used a transposition cipher to encrypt her messages to Bob. For added security, she encrypted the transposition cipher key using a substitution cipher, and kept the encrypted cipher in her computer. Trudy managed to get hold of the encrypted transposition cipher key. Can Trudy decipher Alice's messages to Bob? Why or why not?
Problem 14
You are a spy, and, conveniently, have a library with an infinite number of books at your disposal. Your operator also has such a library at his disposal. You have initially agreed to use Lord of the Rings as a one-time pad. Explain how you could use these assets to generate an infinitely long one-time pad.
Problem 15
Quantum cryptography requires having a photon gun that can, on demand, fire a single photon carrying 1 bit. In this problem, calculate how many photons a bit carries on a 250-Gbps fiber link. Assume that the length of a photon is equal to its wavelength, which for purposes of this problem, is 1 micron. Also, assume that the speed of light in fiber is \(20 \mathrm{~cm} / \mathrm{nsec}\).
Problem 17
A fundamental cryptographic principle states that all messages must have redundancy. But we also know that redundancy helps an intruder tell if a guessed key is correct. Consider two forms of redundancy. First, the initial \(n\) bits of the plaintext contain a known pattern. Second, the final \(n\) bits of the message contain a hash over the message. From a security point of view, are these two equivalent? Discuss your answer.
