Cryptography
Table of Contents
1 Secure Sockets Layer/TLS
1.1 Handshake Protocol
Establish shared secret key using public-key cryptography
1.2 Record Layer
Transmit data using shared secret key
2 Symmetric Encryption
- k: secret key (e.g. 128bits)
- E: encryption algorithm
- D: decryption algorithm
- m, c: plaintext, ciphertext
\[E(k, m) = c\] \[D(k, c) = m\]
Both E and D are public known
2.1 Single Use Key
2.2 Multi Use Key
3 Cipher History
3.1 Substitution Cipher(use substitution table)
- Caesar Cipher: shift by 3 a->d
- Large key spaces: 26 letters -> 26!
3.1.1 Easy to decipher
- Use frequency of English letters. e.g. 'e', 't', 'a'
- Use frequency of pairs of letters(digrams). e.g. 'he', 'an', 'th'