CS 257 - Fall 2020.


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Welcome to CS 257!

Thought for the day

Schneier's Law:

Any person can invent a security system so clever that he or she can't imagine a way of breaking it.

Lecture 2: Crypto. 9/7

Administrivia

  • Office hours (via zoom. Meeting ID 459 434 2854): Wednesday 4 to 6 pm, and by appointment.

  • Complete this online Student Information form. So far, everyone is in EDT time zone.
  • Get a course account for CPSC 257 on the Zoo. When you register for this class, your course account should be created within one hour or so of signing up.
  • Confirm your piazza account.
  • Start the homework assignment: [Assignments]. Demonstrate openssl
  • Python code to help get started: hw1.py.
  • base64
    echo hello | openssl base64
    aGVsbG8K
    
    h is ascii 0150 = 01101000 011010 == 26 == a in base64
  • Google Python Class Most of you seem to know python.

    Lecture

    Chapter 2: Crypto Overview

  • slides: chapter 2 (slide 28)
  • Classic crypto methods

    Chapter 3: Symmetric Key

  • slides: chapter 3 (actually 2-6)
  • slides: chapter 3 4 up

  • Symmetric Key Crypto

    Stream Ciphers

  • Stream Ciphers
  • A5/1 - Shift Registers
  • Shift Register Crypto: Phone / voice is roughly 64K bits per second
  • RC4
  • Stream Ciphers

    Block Ciphers

  • Feistel Cipher
  • Data Encryption Standard (DES)
  • DES S-box
  • Security of DES
  • Block Cipher Notation
  • Triple DES: Not 3 * keys – just 2 keys
  • Advanced Encryption Standard (AES)
  • AES Summary
  • Time for TEA

    Block Cipher Modes

  • Multiple Blocks
  • ECB mode: Never use ECB Mode!
  • CBC mode
  • Counter Mode (CTR): Note: not a typo – E() for decryption!

    Integrity

  • Confidentiality: no unauthorized reading
  • Integrity – not changing data
  • MAC
  • Uses for Symmetric Crypto
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