CS 15

CS 15 -- Homework 2

email paper to cfk@cs.swarthmore.edu by noon Monday, Sept 8

  1. Read P&P pp. 21-36, 40-42, 53-58
  2. You might want to play around with Place Value Method, Addition in Other Bases, Counting in Other Number Bases at Professor Teresa Carrigan's Virtual Office
  3. Skim P&P pp. 36-40, 51-53
  4. Skim S (Stephenson, "Cryptonomicon") pp. 60-154. Still should be a fun.
  5. Read and pay particular attention to S pp. 65-68, 84-92, 126, 144-146, 152-154.
  6. Read the pages 91 to 109 of "Alan Turing: The Enigma". The book is by Andrew Hodges. You must be on a Swarthmore College network to be able to read this file. The book is out of print but there are two copies of the book on 2-hour reserve at Cornell Library. You might want to think about this weeks writing assignment before you read this.
  7. Read iPhone security flaw exposes private data.
  8. Read Pictures meant for boyfriend or girlfriend are ending up on the Internet
  9. Read Your Internet provider is watching you.
  10. Read Study Raises New Privacy Concerns About Facebook.
  11. Read To Aim Ads, Web Is Keeping Closer Eye on You .
  12. Read A Muckraker's Slaying Leaves Russian Province Fearing Crackdown.
  13. Read Gaping Internet security hole discovered
  14. Read The Trolls Among Us
  15. Just in case you think data leaks are rare or don't happen much any more, skim datalossdb.org .
  16. The 1-2 page paper

    Please send your paper by email to: cfk@cs.swarthmore.edu Also, please make sure your name and CS15 HW2 is at the top of any attachements you send.

    1. We use 'mechanical' procedures to do arithmetic (add, subtract, multiply, divide, extract square roots), look up names in the phone book, order the results of Olympic competition, etc.

      Assume that you have no way to represent negative binary numbers. That is, assume all binary numbers are unsigned. Carefully describe a 'mechanical' procedure for a human being (who does not understand arithmetic) to perform binary subtraction. If the human being is given two n-bit binary numbers M and S with S smaller than M, after executing the procedure, they should obtain the correct difference M-S.

      If you cannot do this for binary subtraction, do it for subtraction of two decimal numbers. The purpose of this exercise is to force you to think about how hard it is to precisely describe a procedure. You may assume that the person who is to execute this procedure, can recognize characters, but you may NOT assume that s/he can add, complement, subtract, etc.

    2. Now try to describe what you mean by a 'mechanical' procedure so clearly that you could contemplate arguing sensibly about what can and cannot be accomplished by a 'mechanical' procedure.

    3. Finally suggest one or two topics that you would like to see addressed in seminar this next week.
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