Conventional security protocols such as IP Security, Secure
Socket Layer and VPN are not practical for use in low level
industrial automation networks due to their lack of support for
multicast- and broadcast transmissions [53]. Key distribution
is also problematic in the use of cryptographic algorithms in
industrial networks, as cryptographic keys may be needed by
thousands of devices. Various approaches to key distribution
have been discussed, for example loading keys onto physical
storage and installing them at each device [48], or distributing
keys electronically at install time when other configuration
settings are loaded onto an instrument [54].