APCO Project 25 (“P25”) is a suite of wireless communications protocols designed for public safety two-way (voice) radio systems. The protocols include security options in which voice and data traffic can be cryptographically protected from eavesdropping. This report analyzes the security of P25 systems against passive and active attacks. We find a number of protocol, implementation, and user interface weaknesses that can leak information to a passive eavesdropper and that facilitate active attacks. In particular, P25 systems are highly susceptible to active traffic analysis attacks, in which radio user locations are surreptitiously determined, and selective jamming attacks, in which an attacker can jam specific kinds of traffic (such as encrypted messages or key management traffic). The P25 protocols make such attacks not only feasible but highly efficient, requiring, for example, significantly less aggregate energy output from a jammer than from the legitimate transmitters.