Quiz Entry - updated: 2026.07.14
What are the key parameters of DES and why is it considered insecure today?
DES uses a 56-bit key with 64-bit blocks over 16 Feistel rounds — it's insecure because 2^56 keys can be brute-forced in hours with modern hardware.
DES parameters:
| Parameter | Value |
|---|---|
| Block size | 64 bits |
| Key length | 56 bits (64 bits input, 8 are parity) |
| Rounds | 16 |
| Structure | Feistel network |
History:
- Developed by IBM, adopted as a US federal standard (FIPS) by the National Bureau of Standards (now NIST) in 1977
- IBM's original "Lucifer" design used a longer key; the published standard fixed it at 56 bits — a shortening widely attributed to NSA influence and controversial at the time
- In 1999, the EFF's "Deep Crack" machine (working with distributed.net) recovered a DES key in about 22 hours
Why 56 bits is too short:
- 2^56 = 7.2 × 10^16 possible keys
- Modern hardware (FPGAs, ASICs, cloud computing) can search this space quickly
- DES was officially withdrawn as a standard in 2005
The algorithm itself is well-designed — the weakness is purely the short key length. This is why 3DES was created as a stopgap.
Go deeper:
Data Encryption Standard (Wikipedia) — the 56-bit key controversy, Deep Crack, and withdrawal.