🔐 1. Symmetric Key Encryption

• Single key used for both encryption and decryption.

• Fast and suitable for bulk data encryption.

• Key must be securely shared between parties.

Examples:

• AES (Advanced Encryption Standard): Block cipher, 128-bit block size, supports 128/192/256-bit keys; widely used (e.g., SSL/TLS, disk encryption).

• DES (Data Encryption Standard): 56-bit key; now obsolete due to brute-force vulnerabilities.

• 3DES (Triple DES): Applies DES three times (Encrypt-Decrypt-Encrypt); more secure than DES, but slower.

• RC4/RC5/RC6: Variable key-length ciphers; RC4 is stream-based (deprecated due to vulnerabilities).

• ChaCha20: Stream cipher used in modern TLS (faster than AES on some platforms).

🔑 2. Asymmetric Key Encryption

• Uses a key pair: a public key (encryption) and a private key (decryption).

• Ensures confidentiality and supports digital signatures.

• Computationally intensive; usually used for key exchange or small data payloads.

Examples:

• RSA (Rivest–Shamir–Adleman): Based on factoring large primes; key sizes 2048–4096 bits common.

• ECC (Elliptic Curve Cryptography): Smaller keys, high security (e.g., ECDSA, ECDH); used in mobile devices.

• ElGamal: Based on discrete logarithms; supports encryption and key exchange.

• Diffie-Hellman (DH): Key exchange protocol (not encryption by itself); vulnerable without authentication.

🔄 3. Hybrid Encryption

• Combines symmetric and asymmetric encryption.

• Asymmetric encryption secures the symmetric session key; symmetric encryption handles data payload.

Example:

• TLS/SSL: Uses RSA/ECDH for key exchange, AES/ChaCha20 for actual data encryption.

🧮 4. Hash Functions (One-Way Encryption)

• Not technically encryption, but used for data integrity and authentication.

• Irreversible: output (digest) cannot be converted back to input.

Examples:

• MD5: 128-bit output; deprecated (collision attacks).

• SHA-1: 160-bit output; deprecated.

• SHA-2: Includes SHA-224, SHA-256, SHA-384, SHA-512.

• SHA-3: Keccak-based hash standard.

• HMAC (Hash-based Message Authentication Code): Combines a secret key with a hash function.

📦 5. Other/Legacy/Lightweight Methods

• XOR Cipher: Basic symmetric cipher; insecure alone.

• Caesar Cipher: Shift cipher (classical); easily broken.

• Vigenère Cipher: Poly-alphabetic cipher; classical, insecure today.