An Overview of Cryptography

A technology that provides data confidentiality.

Encryption is the process of converting plaintext into ciphertext.

• Symmetric-key cryptography
  • Block ciphers
  • Stream ciphers
• Public-key cryptography
  • Factoring-based schemes
  • Discrete-logarithm-based schemes
  • Post-quantum cryptography: lattice-based, code-based, and other schemes

• Setup algorithm: $Setup(\lambda ) → {K_{enc}, K_{dec}}$
• Encryption algorithm: $Enc({K_{enc}, M}) → CT$
• Decryption algorithm: $Dec({K_{dec}, CT}) → M$

An encryption method that uses the same key for encryption and decryption.

It is also called secret-key cryptography.

Traditional approaches include block ciphers such as DES, AES, ARIA, and SEED, and stream ciphers such as RC4 and ChaCha.

Advantage: faster than asymmetric encryption.

Disadvantage: key distribution is a problem, and many keys are needed: $N(N-1)/2$ keys.

An encryption method that uses different keys for encryption and decryption.

It is also called public-key cryptography.

Examples include RSA, ElGamal, and NTRU.

Advantages: resolves the key-sharing problem and requires fewer keys: $2N$ keys.

Disadvantage: slower than symmetric encryption.

• Plaintext: the original message or data supplied as input to an algorithm.
• Ciphertext: the output of an encryption algorithm.
• Encryption algorithm: an algorithm that converts plaintext into ciphertext.
• Decryption algorithm: an algorithm that converts ciphertext into plaintext.
• Public key and private key: a pair of keys selected for encryption and decryption, respectively.

An encryption algorithm should remain secure even if it is public. Only the secret key needs to remain protected.

This increases the system's security and makes it easier to communicate with others using different keys.

1. Brute-force attack: tries every possible key to decrypt the ciphertext.
2. Cryptanalysis: analyzes the structure of an encryption algorithm to infer the plaintext.
   • Ciphertext-only attack
   • Known-plaintext attack
   • Chosen-plaintext attack
   • Chosen-ciphertext attack