Guest 7

Lecture 21 - March 1st, 2017

Guest Lecture

By Bruce Kapron

What is Cryptography?

Cryptography refers to a set of mathematical and algorithmic tools designed to provide security properties

  • Secrecy
  • Integrity
  • Authenticity
  • Non-repudiation

Cryptology:

  • -> Cryptography
  • -> Cryptanalysis

Why is this relevant in CS?

  • An important aspect of security for computing and communication systems
  • Enabling new tech / apps (cryptocurrencies, e-voting)
  • Many CS-related tools, techniques and algorithms relevant to building cryptographic systems, and breaking them (cryptanalysis)

What will we do today?

  • Focus on encrytion (secrecy)
  • Some history
  • Modern approaches to private-key encryption
  • The public-key revolution

Crytography vs Security

Bruce Schneir's Article:

Private-key Cryptography

Until 1970's all cryptography was private-key (based on a single key shared by communication parties.)

Symmetric Crypto: Same for encrypt and decrypt

Example

Here, m is the message or plaintect, c is ciphertext, and k is key

Classical Crypto:

  • Substitution ciphers
    • Plaintext letters are replaced by ciphertext letters
    • Monoalphabetic subsitituion is mapped to a unique corresponding
    • Polyalphebetic
  • Transposition ciphers
  • Shift cipher
  • Ceasar cipher
  • Affine cipher
  • General substitution cipher
  • Vigenère cipher
    • Developed by Giovan Battista Bellaso and popularised by Blaise de Vigenère
    • Formal Definition:
  • Kasiski's Method
  • Frequency analysis: A Tool
    • Determines the letter frequencies
      • Ex. Santa Cruz Public Library Chart
  • Attack Models
    • Known plaintext -> General Starter Message
      • EX. Hello, Dear Miss...
    • Chosen plaintext -> know some plaintext
      • EX. Battle of Midway - May 1942
        • Japanese Navy (2 Level Code)
        • US Naval Intelligence (Bolean level 1)
          • Japan figured out the code, but didn't know what AF was
            • Water shortage on midway
            • Water shortage on AF

End of Material for Midterm 2

Beginning of Material for Midterm 3