Local Area Networks (LANs) in Aircraft - FTP Directory Listing - FAA

exposes previously isolated computational systems to new classes of failures resulting from both
accidental as well as intentionally malicious attacks that could affect safety of flight.
Section 7 has suggested specific extensions that are needed to extend current FAA policy to
address the additional threats and issues that occur in networked airborne environments.
Sections 10.1 and 10.3 directly address the adequacy of existing regulations. Because this topic
was a central element of phase 2, the more complete response to this topic occurs in section 10,
with this section primarily being an initial description.
9.9 GROUND-TO-AIR COMMUNICATION.
This report recommends that the signals in space (e.g., radio or satellite communications) used
for ground-to-air communications must use transport security cover (i.e., encryption of the
wireless signal in space occurring at the OSI physical layer). This hinders nonauthorized entities
from eavesdropping upon these communications and discourages attempts to potentially inject
false communication signals into the data stream (e.g., possible man-in-the-middle attacks).
However, these links will remain potentially vulnerable to availability attacks caused by hostile
jamming unless mitigation techniques such as AJ waveforms or LPI/LPD waveforms are used.
9.10 WHAT IS THE EFFICACY OF CYCLIC REDUNDANCY CHECKS WITH RESPECT
TO SECURITY?
Software parts are currently assured, in many cases, by having a 32-bit polynomial cyclic
redundancy check (CRC) wrapped around each part packaged with other identifying information
(aircraft type/serial, system part numbers, software part number, etc.) and then that package is
wrapped within another CRC. This helps to ensure not only nontampering (internal CRC) but
also error-free transmission of the software part and the entire data package (wrapping CRC).
This approach has semantically overloaded the CRC concept to handle two different purposes:
• Polynomial codes (CRCs) are mechanisms commonly used within data communications
to detect and fix transmission bit errors. Industry uses different polynomial coding
techniques in different environments to address specific network requirements. The
wrapping CRC function of the previous paragraph corresponds well with this use case.
• The internal CRC is intended to provide identity and integrity protections for received
software parts.
This study states that it is entirely appropriate to use CRCs as polynomial codes to assist in
transmission bit error detection and correction. This is, after all, the historic reason for which
CRC technology was created.
However, this study states that it is inappropriate and risky (potentially dangerous) to use
internal CRCs to provide identity and integrity protections (i.e., the inner CRC) within
networked environments. The United States and world standard mechanism by which the latter
technique is securely accomplished is by code signing in conformance with the U.S. Federal
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