Encryption Modes and Hash Functions

Goals

Introduce encryption modes and analyze their security
Understand basics of how hash functions operate and rank their potential properties
Connect hash functions to password safety and message integrity

Why do we need modes?
How does Electronic Code Book (ECB) encryption work?
- Is it secure?
- Why/why not?
How does stateful counter mode work?
- Is it secure?
- Why/why not?
How does randomized counter mode work?
- Is it secure?
- Why/why not?
- How does it compare to stateful counter mode?
How does cipher block chaining (CBC) mode work?
- Is it secure?
- Why/why not?
What are two common attacks on CBC mode?
What is a padding oracle?
- How can it be used?

What is the definition of a hash function?
- Do hash functions have keys?
What are four properties a cryptographic function might have?
- How are those properties related?
What are some hash functions that are non-cryptographic?
- Which cryptographic hash functions are currently considered secure? Insecure?
How does the Merkle-Damgard construction build a hash function?
- What property is needed from the compression function?
Why is the strongest collision-resistance guarantee secure only against 2^{n/2} hashes (for a hash that outputs n bits)?
- What’s the connection to the Birthday Paradox?
How can hash functions be used to strengthen password-based systems?