Bits and pieces of some symmetric key cryptography algorithms.

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.

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.