Assignment 5

Due Wednesday March 28, 2018 6:50pm via sakai


Please answer the questions precisely and concisely. Every question can be answered in one or at most a few sentences. I will not have the patience to read long paragraphs or essays and you may lose credit for possibly correct answers.


Text: Ross Anderson, Security Engineering: Chapter 5, pages 129–176
Entire chapter: Cryptography

Feel free to skip:

  • 5.6 unless you’re interested in reading about the design of hash functions.
  • Digital Signature if you’re not interested in the ElGamal signature mechanism.
  • 5.7.3 Special Purpose Primitives, which covers threshold crypt and blind signatures
  • 5.7.4 Elliptic Curve Cryptography
  • 5.7.5 Certification
  • 5.7.6 The Strength of Asymmetric Cryptographic Primitives


1. What is a necessary condition for perfect secrecy?

2. What is a running key?

3. What are the three properties of hash functions?

4. How many messages would you have to try, on average, to find two that have a collision (hash to the same hash value) for an n-bit hash function?

5. What is an s-box in a block cipher?

6. What is an advantage of counter encryption (CTR) over cipher block chaining (CBC)?