The data encryption standard (DES) functions use a 56-bit key to encrypt user data. If two credential users (or principals) know the same DES key, they can communicate in private, using the key to encrypt and decrypt data. DES is a relatively fast encryption mechanism. A DES chip makes the encryption even faster; if the chip is not present, though, a software implementation is substituted.
The risk of using just DES is that, with enough time, an intruder can collect enough cipher-text messages encrypted with the same key to be able to discover the key and decipher the messages. For this reason, security systems such as Secure RPC change the keys frequently.