Lifetimes of keys in cryptographic key management systems

The keys lifetimes necessary to attain a certain low disclosure rate have been investigated for two types of schemes. DES is employed as an encryption algorithm example. This paper employs the poorest attack, namely the exhaustive attack as a cryptanalysis. There may be a more effective attack. As results, we recommend to adopt SCHEME 2 and to change the master key ‘at least’ within a few years.