Steve Miller and Clifford Neuman , the primary designers of Kerberos version 4 ( which used the DES encryption algorithm with 56-bit keys ) , published that version in 1989 , although they had targeted it primarily for Project Athena . Steve Miller and Clifford Neuman , the primary designers of Kerberos version 4 , published that version in the late 1980s , although they had targeted it primarily for Project Athena .