  Some recent incidents have shown that possibly the vulnerability of IT
systems in railway automation has been underestimated. Fortunately, so far,
almost only denial-of-service attacks were successful, but due to several
trends, such as the use of commercial IT and communication systems or
privatization, the threat potential could increase in the near future. However,
up to now, no harmonized IT security risk assessment framework for railway
automation exists. This paper defines an IT security risk assessment framework
which aims to separate IT security and safety requirements as well as
certification processes as far as possible. It builds on the well-known safety
and approval processes from IEC 62425 and integrates IT security requirements
based on the ISA99/IEC62443 standard series. While the detailed results are
related to railway automation the general concepts are also applicable to other
safety-critical application areas.
