CS 2000 - Fall 2025.


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Welcome to CS 2000! 11/19/2025

Video of the Day

Crypto! Mark Stamp.

  • Chapter 2, part 1, Information Security: Principles and Practice

  • Chapter 2, part 2, Crypto Basics --- Simple Substitution

  • Chapter 2, part 3, Crypto Basics --- double transposition, one-time pad

  • Chapter 2, part 4, Crypto Basics --- VENONA, codebook cipher, Zimmerman telegram

  • Chapter 2, part 5, Crypto Basics --- crypto history, ciphers of election of 1876

  • Chapter 2, part 6, Crypto Basics --- crypto history, Claude Shannon

  • Chapter 2, part 7, Crypto Basics --- taxonomy of cryptography, taxonomy of cryptanalysis

    Logical problem of the day

    What does the following series represent? What is the next number?

    1991, 1993, 1999, 2017, 2019, 2023, ...

    https://pollev.com/slade You may also download the app to your phone. Use the "slade" poll id.

    Poem of the Day

    From Claude Sonnet 4
    **The Key We Share**
    
    Something there is that doesn't love a secret,
    That sends the frozen-ground-swell under it,
    And spills the upper boulders in the sun;
    And makes gaps even two can pass abreast.
    The work of hunters is another thing:
    I have come after them and made repair
    Where they have left not one stone on a stone,
    But they would have the rabbit out of hiding,
    To please the yelping dogs. The gaps I mean,
    No one has seen them made or heard them made,
    But at spring mending-time we find them there.
    
    Yet here we walk with matching keys in hand,
    The same small cipher that will lock and free
    Our messages from prying winter eyes.
    My neighbor moves in darkness as he will,
    But when he speaks his words through my device
    They come as clear as morning over snow.
    We meet upon the boundary of trust
    Each spring to test our shared arithmetic—
    Good fences make good neighbors, some have said,
    But better still: one key for you and me.
    
    I wonder if he thinks as I do now:
    How strange that the same key that hides our words
    Is what reveals them, like the melting frost
    That shows the stones we laid the fall before.
    There where it is we do not need the wall:
    Encryption is the wall we carry with us.
      

    This poem channels Frost's contemplative voice and his exploration of boundaries, shared work, and human connection, while weaving in the essential concept of symmetric ciphers—that the same key both encrypts and decrypts, creating a bond of trust between those who share it.

    Canvas Quiz of the Day (need daily password)

    Most days, there will be a simple canvas quiz related to the lecture. You need a password to activate the quiz, which I will provide in class. These quizzes will count toward your class participation grade. The quiz is available only during class. Note: each quiz is now worth 5 points.

    Click for today's quiz.

    Lecture 23: Cryptography.

    Administrivia

  • Final exam date has been announced: Monday, December 15th at 9am. RTBA. (See below)

  • I have office hours Wednesdays from 4-6 pm, on Zoom, ID 459 434 2854. NOT NEXT WEEK

  • I will be available for lunch on Mondays at 1 pm in Morse. NOT NEXT WEEK

  • ULA office hours are found at Ed Discussions on Canvas.

  • CS Peer Advisers. Fall 2025 Peer Advisors Office Hours Schedule.

  • Homework assignments: [Assignments]. hw7 is now available.

    Announcements

  • Yale Information Society Project See this week's events.

    CPSC 4580: Automated Decision Systems.

    Yale AI Lab Showcase Discussion of CPSC 458.

    AI Policy

    This is a course about decision making, with an emphasis on creating computer programs that make decisions in a manner similar to human cognition. We are interested in cognitive process models. As such, we will often engage in introspection to examine our own decision thought process.

    Now is such a moment. I have decided not merely to permit the use of AI tools in the course, but to encourage it. That is, I want the students to learn how to use AI to write better code as well as to refine their own ideas. Here is my own thought process.

    Final Exam

    Monday December 15th, 9am. RTBA.

    Here is a practice final exam and practice final solutions.

    Here are the important concepts from Stamp:

    Plus concepts from hw7 including xor, base64, shell scripts.

    Shell scripts: I might ask you to write a shell script. You should know the for loop.

    The following topics were part of this course and are in scope for the final:

    If your grade on the final exam is higher than your lower midterm grade, it will replace that grade. The quality of mercy is not strained.

    Alas, we did not get to machine learning. See scikit learn aka, sklearn. Python module for machine learning. Machine learning jupyter notebook

    Cryptography

    XZ Utils backdoor insecure open source supply chain.

    Cryptography notebook Chapter 2, slide 10.

    See hw7hints.py You may need to install the module: wordsegment. (May need to run on lion using python 3.10. Sigh.)

    pip install wordsegment
      

    Getting to know UNIX

    UNIX Introduction Principle 5.
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