Matt Blaze

Department of Computer Information Science

"One-way cryptography and two-way communications"

 

Abstract

PCO Project 25 (``P25'') is a ``secure'' wireless communications protocol used in the US and elsewhere for public safety two-way (voice) radio systems. Last year, we found a number of protocol, implementation, and user interface weaknesses that routinely leak information to a passive eavesdropper and that permit highly efficient and difficult to detect active attacks, which we will discuss briefly.  For example, an active attacker with very modest resources can prevent specific kinds of traffic (such as encrypted messages) from being received, while emitting only a small fraction of the aggregate power of the legitimate transmitter. We also found that even passive attacks represent a serious practical threat. In a study we conducted over a two year period in several US metropolitan areas, a significant fraction of the ``encrypted'' P25 tactical radio traffic sent by federal law enforcement surveillance operatives is actually sent in the clear, in spite of their users' belief that they are encrypted, and often reveals such sensitive data as the names of informants in criminal investigations.

 

This talk will examine the P25 protocol and its failures as an example of a largely ignored problem in cryptography and security: ``one-way' communications, in which the message sender makes all security policy decisions. One-way protocols are surprisingly difficult in practice, and represent some of the most important unsolved security problems in moden computing.  Perhaps insight into how the P25 protocol failed will give us some insight in to how to secure electronic mail and messaging protocols.

 

This is joint work with Sandy Clark and Perry Metzger.

 

 

Refreshments will be served on the

2nd Floor Mezzanine Level

outside Wu & Chen

immediately following the talk.

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