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CS 170 Homework



Chapter 3



Note that the answers to the odd-numbered problems can usually be found in the back of the book. Your homework may sometimes be collected and graded, but is mainly intended for practice. Get as much practice as you can. See me or the tutors on any type of problem that you cannot handle. You may also be asked in class to explain how to solve some of the homework problems. Quiz questions are likely to be similar to recent homework questions.
  • Fri, Oct 9, Section 3.2, Numbers 1abc, 7a, 15, 19, 21a
    In these problems, use the theorems and figure 3 whenever possible. Do not use the definitions unless you see no other way to proceed. (This supersedes the book's directions for exercises 1 - 14.)
  • Mon, Oct 12, Section 3.2 again, will collect Number 20ab
    Section 3.3 (not collected), Numbers 4, 7, 8, 10
  • Fri, Oct 16, Section 3.4, Numbers 1, 3, 9, 17, 19, 26a, 29
  • Fri, Oct 23, Section 3.6, Numbers 1a, 3ac, 5a, 8c, 9, 15, 19, 23bc, 49, 50
  • Mon, Oct 26, Section 3.7, Numbers 1bc, 5, 7, 11, 27ab.
  • Write up to turn in on Fri, Oct 30:
    A) Much like in Example 11, use RSA with p = 41, q = 67, and e = 17.
    1. Find n.
    2. Find (p - 1)(q - 1).
    3. Find d, the inverse to e modulo (p - 1)(q - 1). If you get a negative number for d, use instead the smallest positive number that is equivalent to it mod (p - 1)(q - 1).
    4. Encrypt the message MATH. First break it into 2 parts and convert each letter to a 2-digit number with A being 00, B being 01, C being 02, ..., Z being 25. Encrypt each of the 2 parts separately. Optional: Use n and d to decrypt the 2 parts to show that it works.
    B) Suppose your public encryption key uses n = 2627 and e = 11. Your private decryption key uses n = 2627 and d = 2291. You receive the message 0107 1712 0568 1586 which has been encrypted with your public encryption key. Use n and d to decrypt this message. (Similar to Example 12.)


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Last updated: October 28, 2009
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