Introduction to Cryptography

Goals

• Define basic crypto terminology
• Define the notion of perfect secrecy and explain its limitations
• Summarize the importance of obtaining true randomness and challenges in doing so

Crypto history

• How can substitution ciphers be broken?
• What distinguishes modern cryptography from everything before 1945?
• What differs between symmetric and asymmetric crypto?
• What are some examples of “exotic” cryptography?

Crypto Goals

• What three properties does a secure channel provide?
  • What makes them distinct?
  • Why do we need all three?
• Symmetric Cryptography
  • What three algorithms constitute a symmetric key cipher?
  • How is correctness defined?
• How does a one-time pad work?
  • What happens if you use it more than once?
  • Does it provide integrity?
• Perfect Secrecy
  • How is it defined?
  • How can we achieve it?
  • What’s the “bad news” in the bad-news theorem?

Randomness

• Where does randomness play a role in secure systems?
• How can randomness acquisition go wrong?
• How can you obtain true randomness?