Can They Hear Me Now?: A Security Analysis of Law Enforcement Wiretaps

Although modern communications services are susceptible to third-party eavesdropping via a wide range of possible techniques, law enforcement agencies in the US and other countries generally use one of two technologies when they conduct legally-authorized interception of telephones and other communications traffic. The most common of these, designed to comply with the 1994 Communications Assis-tance for Law Enforcement Act (CALEA), use a standard interface provided in network switches. This paper analyzes the security properties of these inter-faces. We demonstrate that the standard CALEA interfaces are vulnerable to a range of unilateral attacks by the inter-cept target. In particular, because of poor design choices in the interception architecture and protocols, our experiments show it is practical for a CALEA-tapped target to over-whelm the link to law enforcement with spurious signaling messages without degrading her own traffic, effectively pre-venting call records as well as content from being monitored or recorded. We also identify stop-gap mitigation strategies that partially mitigate some of our identified attacks