Cryptography

a. Secure Communication

b. Secure Socket Layer / TLS
 - Standard for Internet security
 - Handshake Protocol: Establish shared secret key using public-key cryptography
 - Record Layer: Transmit data using negotiated key. Our starting point: Using a key for encryption and integrity

c. Protected files

d. Building block: sym.encryption

e. Use Cases
 - Single use key (one time key)

• Key is only used to encrypt one message
• Encrypted email: new key generated for every email
• No need for nonce (set to 0)

 - Multi use key (many time key)

• Key used to encrypt multiple messages
• SSL: same key used to encrypt many packets
• Need either unique nonce or random nonce

f. First Example: One Time Pad

g. Stream ciphers

h. Danger in using stream ciphers