Week 3

Vorlesung - 27/10/25

chapter 2: cryptography

• basic notions
• classification
• cryptographic hash functions

Basic Notions & Motivation

• why encryption (Verschluesselung)?
• cryptology: kyrptos = hidden, logos = word. how to communicate securly
  • cryptography: hidden, graphein = writing. Creating encrypted text
  • cryptoanalysis: “solving” encrypted text
• basic notions of cryptoanalysis:
  • classical cryptoanalysis
  • imiplementation attacks
  • social-engineering attacks
  • Kerckhoff’s Principle: system should be secure even if everything about the encyrpiton algorithm is known, except the key. (opposite of security by obscurity)
  • symmetric cryptographic algorithms vs assymetric cryptographic analysis
    • symmetric = there’s only one key to encrypt the text
    • assymetric = there’re two different keys. \(\Rightarrow\)
  • cryptographic hash-function (the actual encryption)
    1. compression
    2. computation cost must be low
    3. inverse function resistence
    4. weak collision resistence (second inverse function resistence property)
    5. strong collision resistence (collision resistence)