Costin, a computer scientist and graduate student at Eurecom, outlined a series of issues related to the Automatic Dependent Surveillance-Broadcast (ADS-B) system, which is being installed as a replacement to the decades-old ground radar system used to guide airplanes through the sky and on the ground at airports.
Among the threats to ADS-B is that the system lacks a capability for message authentication. "Any attacker can pretend to be an aircraft" by injecting a message into the system, Costin said.
There's also no mechanism in ADS-B for encrypting messages, so messages related to air traffic--including the ability to identify aircraft, their location, and altitude--can be read by virtually anyone, Costin said. He displayed an air traffic screen capture, taken this year, which ostensibly showed the in-flight location of Air Force One, the Boeing 747 used to transport President Obama.
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If the aircraft was in fact Air Force One, the easy availability of that information would have national security implications. "It's a very high-profile target," said Costin. On the other hand, it's possible that the aircraft represented in the screen capture wasn't Air Force One, but another plane identified within ADS-B using Air Force One's registration code. "If the data is false, somebody is spoofing the system," said Costin.
Costin did not provide evidence of any known attacks on ADS-B. Rather, he presented a theoretical scenario in which someone injected the system with data on "fake planes," forcing the air traffic control system to adjust to aircraft that weren't actually in flight. He characterized such an attack at scale--with one million fake planes, for example—as comparable to a denial-of-service attack on the air traffic control system. Air traffic controllers might be forced to block off air space while they sorted out the mess, he said.
Costin demonstrated how an attack on ADS-B could be mounted using inexpensive software-defined radios. He took airplane data that was publicly available from the system, modified the data, and "replayed" the data back to a commercial receiver. "The possibility of injecting fake airplanes is quite easy, just by taking a real message and crafting it to your needs," he said.
There are also privacy issues, because data on private planes can be culled from ADS-B as well. By matching that data with aircraft registration databases, Costin explained, it would be possible to track non-commercial aircraft from city to city.
In a whitepaper accompanying his presentation, Costin wrote that the types of potential attacks on ADS-B range from passive attacks such as eavesdropping to active attacks, including message jamming and injections of the type he demonstrated.
In addition to the lack of encryption in ADS-B, the whitepaper identifies the following security weaknesses: no use of entity authentication as a way of protecting against message injection, or of message signatures to deter tampering; no challenge-response mechanisms to protect against replay attacks; and lack of "ephemeral identifiers" for privacy protection.
Questions over the security of the ADS-B system aren't new. Aviation experts have warned of vulnerabilities in the past, but the FAA has been reluctant to discuss them. In response to InformationWeek, the FAA, in a prepared statement, said it has "a thorough process in place" to identify possible risks to ADS-B, such as intentional jamming, and that it has taken steps to mitigate risks uncovered as part of an ADS-B security action plan. The agency declined to identify the risks it has identified or addressed, calling them "security-sensitive."
"The agency conducts ongoing assessments of ADS-B signal vulnerabilities," according to the statement. The FAA said the contract for the ADS-B ground station network requires ongoing independent validation of the accuracy and reliability of ADS-B and aircraft avionics signals. As a backup to ADS-B, the FAA plans to maintain about half of the current network of secondary radars "in the unlikely event it is needed."
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