Classical Cryptography

Private-key Cryptography

Symbols

Encryption and Decryption Process

• Key-generation:

  Use the algorithm $Gen$ to generate a secret key $k \in K$

• Encryption:

  Input the secret key $k$, and a message $m \in M$

  Output the ciphertext $c$

  $$c \gets Enc_k(m)$$

• Decryption

  Input the secret key $k$, and the ciphertext $c$

  Output the plaintext $m$, or an error

  $$m \coloneqq Dec_k(c)$$

Kerckhoffs’s Principle

• The encryption scheme is not secret
  • The attacker knows the encryption scheme
  • Only the key is secret
  • The key must be chosen randomly, and be kept secretly