Symmetric Cryptography Concepts

Symmetric Cryptography
- Key Sharing: Both the sender and the receiver share a common secret key for encryption and decryption.
- Security: Larger key sizes (greater than 128 bits) provide better security.
- Time-Stamping: Can be used to counter replay attacks by adding a timestamp.
- Limitations: Does not provide built-in mechanisms for authentication and non-repudiation.
Data Encryption Standard (DES)
- Origin: Developed by IBM.
- Specifications: Uses a 64-bit block size and a 56-bit key with 8 bits for parity.
- Rounds: Involves 16 rounds of substitution and transposition, implementing confusion (concealing the statistical connection between ciphertext and plaintext) and diffusion (spreading the influence of plaintext over many ciphertext characters).
- Triple DES (3DES): Applies DES encryption three times, preferably with three different keys, offering an effective key length of 168 bits through 48 rounds of computation (3×16).
- Replaced By: Advanced Encryption Standard (AES).
Advanced Encryption Standard (AES)
- Selection: Chosen by NIST in 2001 as the replacement for DES.
- Usage: Widely used in applications like BitLocker (full disk encryption) and Microsoft EFS (file and folder encryption).
- Key Sizes: Supports 128, 192, and 256-bit keys with a block size of 128 bits.
- Algorithm: Based on the Rijndael Block Cipher Algorithm, known for speed, simplicity, and resistance to known attacks.
Other Symmetric Algorithms
- RC5: A variable block cipher with key sizes up to 2048 bits, developed by Rivest, Shamir, and Adleman (RSA).
- IDEA (International Data Encryption Algorithm): A 64-bit block cipher with a 128-bit key, known for its use in PGP software.
- Twofish: A 256-bit key cipher with 128-bit blocks and 16 rounds, based on Blowfish, though not selected for AES.
- Blowfish: Created by Bruce Schneier, with key lengths ranging from 32 to 448 bits, commonly used in Linux systems with bcrypt as an alternative to DES.