"Two Australia Security researchers, Stephen Glass and Matt Robert have published a paper that details flaws in the encryption implementation (PDF) in the APCO Project 25 digital radio standard, used by emergency services and police departments world-wide. The paper details flaws in the DES-OFB and ADP encryption that enable the encryption key to be recovered by traditional brute force key searching. Also detailed is a DoS attack that makes use of unauthenticated radio inhibit mechanism. The research is part of the OP25 project, which uses GNUradio to implement a P25 stack using software defined radio. With this solution in place, the researchers were able to do detailed analysis of the traffic coming from various radio systems and to transmit and receive to P25 radios in their lab."
http://www.nicta.com.au/pub?doc=5076
http://www.nicta.com.au/pub?doc=5076
