Stefan Katzenbeisser, speaking at the Chaos Communication Congress in Berlin, said the systems that switch trains from one line to another could be shut down if encryption keys went astray, the BBC reported Wednesday. Trains would not be in danger, he said, but there could be delays.
Train-switching systems have historically been controlled by proprietary analogue systems, with more than 35 incompatible systems in use for railway communications across Europe.
A group of manufacturers decided to switch to a single digital standard and developed GSM-Railway, a more secure version of the 2G wireless standard used by mobile phones.
GSM-Railway allows traffic controllers and train drivers to talk to each other, and for data on a train's speed and location to be communicated to control centers, for use in giving trains permission to enter the next part of the track.
Encryption keys, used to protect the communications, could pose risks if they fell into the wrong hands, Katzenbeisser said, allowing hackers to overwhelm the system and shut it down.
"Trains could not crash, but services could be disrupted for some time," he said.