DES is based on a Feistel network, with a Feistel function composed on expansion (from 32 bit to 48), key-mixing (with a 48 bit subkey), S-boxes and finally a permutation of the 32 bit output.
DES is now considered insecure due to its small key size which allows brute-force attacks.
DES, the Data Encryption Standard, was the standard US block cypher from 1976 until AES came out in 2001. It was delisted in 2004 and withdrawn as a national standard in 2005.
