01: Intro to keeping shit secret

Introduction to information security. Old school crypto.

Keypair Hash PKI Certificate SSL\/TLS Plain text Message to encrypt Cipher Text Encrypted Message Key Secret that transforms plain text to cipher text Keyspace Possible set of keys regular symmetric key

Security rules

1: Don't roll your own software implementation\/crypto primitives

don't make your own software implementation or cyptographic primitives! you're not a highly experienced security designer\/implementer!!!

Kerckhoff's Principle

even if algorithm is known, crypto system should be secure!
system should depend on secrecy of the key, NOT the algorithm!

Historical Ciphers (stream ciphers)

Caeser Cipher

encrypt by shifting letters down the alphabet, decrypt by shifting back
FLAW: freq still same, b\/t encrypted and unencrypted
FLAW FIX: remove spaces
rings with letters on top of other rings with letter => 25 non trivial encryptions

Vigenere Cipher

Write message, passphrase underneath (repeaet as necessary)
add message to password mod 26 (start count @0)
FLAW: if you know the passcode you know the message (frequency not a problem)

Enigma

key press closes circuit, lighting up a cipher text, each key press rewires the machine
keys changed on a regular basis
FLAW: human error and subtle design flaws (A letter cannot go to itself - what plaintext ISN'T)
26^3 possible keys, with everything else, 2^70 - able to brute force

One-time Pad

perfect secrecy - no amount of computers can help since cipher text can decrypt to ANY message given corresponding pad, and all pads are equally as likely
- pad is chosen independently at random
- pad is exactly as long as the message
- pad only ever used once
not practical:
- generating and storing pad...
- |pad| = |message|
- human error (pad reuse, alignment, etc.)

01: Intro