P25 Officials Request Information on Low Speed Data to Enhance Security (10/28/13)
Monday, October 28, 2013 | Comments

The Project 25 (P25) Steering Committee and manufacturer members of the Telecommunications Industry Association (TIA) have taken steps to address a number of security issues through the joint APCO Project 25 Interface Committee (APIC).

The APIC Encryption Task Group (ETG) defined a solution for Link Layer Security, also known as Link Layer encryption, and would like to make use of the Low Speed Data (LSD) field defined by the Phase 1 FDMA Common Air Interface (CAI) standard (102.BAAA-A) to implement this feature.

The FDMA CAI standard identifies 32 bits of information referred to as LSD that are continuously transmitted whenever a P25 transmitter is keyed, but the TIA 102 P25 standards have never specified a use for these bits. The LSD field is only present for FDMA conventional and FDMA trunking voice signaling. The LSD field is not used on FDMA data channels, FDMA control channels or TDMA voice channels.

As an example of a use for these LSD bits, in the 1990s, Union Pacific Railroad identified a methodology by which these bits could be used to continuously send location information (lat/lon) while its GPS-equipped transmitter was active. However, to the knowledge of Steering Committee and TIA members, no device using these bits in any manner has been fielded.

Before reassigning the 32 LSD bits for use by Link Layer Encryption, the APIC Encryption Task Group would like to determine if any manufacturers or users have knowledge of any FDMA conventional or trunking air interface implementations that may be using these 32 bits of LSD.

P25 systems are open to outside tampering such as spoofing and replay of trunking control and voice messages, as well as adversely controlling the behavior of subscriber radios such as by sending out a rogue command to "kill" users’ radios. A widely distributed 2010 technical report by the University of Pennsylvania titled "Security Weaknesses in the APCO Project 25 Two-Way Radio System” revealed the vulnerabilities.

The weaknesses are not unique to P25 and exist to some extent with all major analog and digital product lines, a statement said. While acknowledging that no such actual attack has ever been reported on any radio system, P25 officials are conscious of the potential problems that could result from these vulnerabilities and are actively implementing enhanced security options to protect against them.

If you have any information regarding any FDMA Air Interface implementations using these bits, contact P25 Steering Committee member John S. Powell by email jpowell@berkeley.edu.

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