Symmetric encryption uses the same key for both encryption and decryption, while asymmetric encryption uses a pair of keys - a public key and a private key.

Symmetric Encryption:

• Same key for encrypt/decrypt
• Faster performance
• Key distribution challenge
• Examples: AES, DES, 3DES

Asymmetric Encryption:

• Public/private key pair
• Slower performance
• Solves key distribution problem
• Examples: RSA, ECC, DSA

Example scenario: If Alice wants to send a message to Bob using symmetric encryption, they both need to have the same secret key beforehand. With asymmetric encryption, Bob can share his public key openly, and Alice can encrypt messages that only Bob can decrypt with his private key.

AES (Advanced Encryption Standard) is a symmetric encryption algorithm adopted by the U.S. government and used worldwide. It replaced DES as the standard encryption algorithm.

Key features:

• Block cipher operating on 128-bit blocks
• Key sizes: 128, 192, or 256 bits
• Highly secure and efficient
• Resistant to known cryptographic attacks
• Fast implementation in both hardware and software

Why it's widely used:

• Strong security with no known practical attacks
• Excellent performance
• Standardized and well-tested
• Available in most cryptographic libraries
• Required for many compliance standards

AES is used in everything from HTTPS connections to file encryption and VPNs.