DES
The Data Encryption Standard (DES) is the symmetric block cipher standardized in 1977, using a 56-bit key and 64-bit blocks; it is obsolete due to its short key.
Purpose
It provided standardized symmetric encryption for banking and government, once the de facto standard, and has been replaced by AES.
Mechanism
It is a 16-round Feistel network. Each round splits the 64-bit block into halves; the right half passes through an expansion permutation, XOR with the subkey, S-box substitution, and P permutation, then XORs into the left half. Only 56 of the key bits are effective (the 8th bit of each byte is parity).
Use cases
- Legacy ATM and financial systems
- Historical cryptography research
- Teaching examples (Feistel structure)
- Old Kerberos versions
Examples
- Input
key=56bit, data=8bytesOutput8-byte ciphertextBroken by brute force
Common errors
- Still using DES in new systems
- Migrate to AES-256
Related terms
AES
The Advanced Encryption Standard (AES) is the symmetric block cipher NIST standardized in 2001, supporting 128/192/256-bit keys, and is the de facto standard of modern encryption. GLOSSARY
3DES (Triple DES)
Triple DES (3DES) strengthens DES by encrypting each data block three times with 56-bit keys in an encrypt-decrypt-encrypt (EDE) sequence, yielding 168 bits of key material, and served as the transitional cipher between DES and AES. GLOSSARY
Block Cipher
A block cipher is a symmetric cipher that encrypts and decrypts fixed-length blocks (e.g., 128 bits) and requires a mode of operation to handle arbitrary-length data. GLOSSARY