DES Encrypt / Decrypt

What is DES encryption?

In July 1998 the Electronic Frontier Foundation built a machine from 1,856 custom chips for roughly $250,000 and recovered a DES key in 56 hours. The following January, distributed.net and that same machine did it in 22 hours and 15 minutes. DES had been the U.S. federal standard for twenty-one years, and the demonstration ended the argument about whether 56 bits was enough.

DES encrypts 64-bit blocks under a key with 56 effective bits — 2^56 possibilities, a space that commodity cloud hardware now walks through in minutes rather than hours. It is offered here for decrypting legacy material and for study, never for protecting anything new. All five modes are available: CBC, CFB, CTR, OFB, and ECB.

The standard's origins explain some of its shape. IBM's Lucifer cipher was submitted to the National Bureau of Standards, revised with input from the NSA, and published in 1977 as FIPS 46 with the key shortened from Lucifer's 112 bits to 56 — a reduction that drew immediate criticism from Diffie and Hellman, who argued that year that a purpose-built cracking machine was already affordable to a well-funded adversary. NIST withdrew the standard in 2005.

What survives DES is its structure rather than its security. The Feistel network it popularised — splitting each block in half and running a round function so that decryption is encryption with the key schedule reversed — reappears in Blowfish, Camellia, and dozens of later designs. Its S-boxes were the first widely studied example of deliberately non-linear substitution, and the NSA's unexplained adjustments to them turned out, once differential cryptanalysis was published openly in 1990, to have hardened the cipher against precisely that attack. For anything you actually need to protect, use AES-256; for how the families compare, see our encryption algorithms guide.

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