The document summarizes encryption methods for strong security. It discusses how data, file, and link encryption work to protect private information when using the internet and storing files locally. Data encryption buries real data in pseudorandom noise. File encryption protects local data from physical intrusion. Link encryption encrypts and decrypts all traffic between communication endpoints. A key is a piece of information that determines the output of cryptographic algorithms, and is needed for encryption and decryption to work.