Data Encryption Standard (DES)
Designed by IBM in 1975, with help from NSA
Keys are 56 bits long, so there are 256 keys, or about 70,000,000,000,000,000
256 is a big number, but not that big. In August 1998, the Electronic Frontier Foundation demonstrated that a special-purpose machine built from standard parts at a cost of $200,000 could break DES in 56 hours.
Big governments have a lot more than $200,000 to spend on cryptanalysis.
Each time you add a bit to the key length, you double the time required to break the system.
NIST is accepting candidates for a new encryption standard.