DES in brief
DES, the Data Encryption Standard, was designed at IBM and published by the US National Bureau of Standards (now NIST) as FIPS 46 in 1977. For more than 20 years it was the standard block cipher. It is a Feistel cipher.
| Block | 64 bits: the plaintext is cut into blocks of 8 bytes |
|---|---|
| Key | 64 bits, but only 56 are used: every 8th bit is a parity bit |
| Rounds | 16, each with its own 48-bit round key K₁ … K₁₆ from the key schedule |
| Structure | IP → 16 Feistel rounds → swap → IP⁻¹. Decryption: the same steps, round keys in reverse order |
| Function f | 32 bits in → expansion E: 48 bits → ⊕ Kᵢ → 8 S-boxes (6 → 4 bits) → permutation P: 32 bits out |
| Today | 2⁵⁶ ≈ 7.2 · 10¹⁶ keys is too few: in 1998 the EFF machine “Deep Crack” found a DES key in 56 hours. AES replaced DES in 2001. Triple DES (three DES operations) was used longer and is now retired too. |
The charts below show the whole cipher (A), the function f (B) and the key schedule (C). Press Step or click a block.