Basic Terminology

• plaintext → The original message
• ciphertext → the coded message
• cipher → algorithm for transforming plaintext to ciphertext
• key → info used in cipher known only to sender/receiver
• encipher (encrypt) → converting plaintext to ciphertext
• decipher (decrypt) → recovering ciphertext from plaintext
• cryptography → Study of encryption principles/methods
• cryptanalysis (codebreaking) → the study of principles/methods of deciphering ciphertext without knowing key
• cryptology → the field of both cryptography and cryptanalysis

The language of cryptography

Plain Text → encryption algorithm → ciphertext → decryption algorithm → Plaintext

• Symmetric key crypto: Sender, and receiver keys identical
• public-key crypto: encryption key public, decryption key secret (private)

Symmetric Encryption

• Conventional / secret-key / single-key
• sender and recipient share a common key
• all classical encryption algorithms are private key
• it was the only type before the invention of public-key in the 1970s

Symmetric Cipher Model