CS338 Computer Security
Friday, 22 September 2023

+ A few notes on our symmetric crypto avatar: AES
    (also some notes on Unix command shells & openssl)

- Look at the AES Wikipedia page for some basics if you're interested
- How big is the block size?
- What happens if each block is encrypted independently?
    [think: watching an encrypted texting exchange or web session]
  This is called "electronic code book (ECB) block cipher mode" and it's bad

- Digression: Unix pipelines can do tons of cool stuff:

    openssl rand 16 | od -An -tx1 | tr -d ' \n'

But if there's a cryptographic thing you want to do, maybe openssl can
already do it:

    openssl rand -hex 16

Browse the manual pages and help output. It's fun!

- Digression: Unix command shell tricks: environment variables, echo, $(), ``

- Change one bit in your key:

- Change one bit in your plaintext:

+ Kerckhoffs' Principle
- "the security of a cryptosystem must lie in the choice of its keys only; everything else (including the algorithm itself) should be considered public knowledge."
https://link.springer.com/10.1007%2F978-1-4419-5906-5_487#:~:text=Kerckhoffs'%20Principle%20states%20that%20the,should%20be%20considered%20public%20knowledge.

+ Questions, comments,...
- Basic Authentication
- AES w/ openssl
- Videos
- Wireshark
- News stories
- Whatever

+ Next
- Key exchange with Diffie-Hellman
- Asymmetric encryption with RSA