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Homework 08: Debugging and Profiling + Security and Cryptography

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Exercises

  1. Entropy (3 points). Put each answer in a new line of a file entropy.
    1. Suppose a password is chosen as a concatenation of four lower-case dictionary words, where each word is selected uniformly at random from a dictionary of size 100,000. An example of such a password is correcthorsebatterystaple. How many bits of entropy does this have? (Round to the nearest integer.)
    2. Consider an alternative scheme where a password is chosen as a sequence of 8 random alphanumeric characters (including 10 numbers, and lower-case and upper-case letters). An example is rg8Ql34g. How many bits of entropy does this have? (Round to the nearest integer.)
    3. Which is the stronger password? (Please write 1 or 2.)
  2. Symmetric cryptography. Decrypt sym.enc using AES encryption with openssl aes-256-cbc -d -in {input filename} -out {output filename} -md sha256. The password we used to encrypt the file is 1234. Save the output file in sym.
  3. Asymmetric cryptography. In this homework, you will find two files, public.pgp and private.pgp, corresponding to a set of public and private keys. (This set of keys was generated with the password 1234.) You will also find a file asym.asc, which is a file encrypted with GPG. Your job is to decode this message into a file asym.