24 Oct 2025
Symmetric Key Cryptography
symmetric key cryptography
DES properties
- Every 8th bit in DES is treated as a parity bit.
- Out of 64 bits, only 56 are used.
- Based on Feistel networks.
- Obsolete, if anything 3DES is recommended.
- Three key (168 usable bits), or Two key (112 usable bits) are permitted.
- Two key solution reuses K1.
- Combination used is E-D-E mode (enc - dec - enc).
AES properties
- Based on Rijndael algorithm, that received multiple entries.
- Data always processed in blocks of size 128 bits.
- Key size, 128, 192, 256 bits.
- Has multiple modes discussed below.
RC4 and ChaCha20
- Work by XORing a pseudo-random byte generator dependent on a secret key.
- Mostly works by permuting an array based on a key, and later using that array as an internal state to generate pseudo random bytes.
- ChaCha20 additionally uses a nonce. Nonce is 96 bits and key is 256 bits.
