Uses a single common key for encryption and decryption.

Faster and simpler but key exchange is a challenge.

• Data Encryption Standard (DES)

• Advanced Encryption Standard (AES)

Uses a pair of keys: public key for encryption and private key for decryption.

More secure but slower.

• RSA (Rivest-Shamir-Adleman)

• Elliptic Curve Cryptography (ECC)

Do not require keys.

Convert input into fixed-length hash value.

One-way function.

Examples:

• SHA-1

• SHA-256

• MD5

• MD6