Editing Project 25 (section)

====Traffic analysis and active tracking====
Certain metadata fields in the Project 25 protocol are not encrypted, allowing an attacker to perform [[traffic analysis]] to identify users. Because Project 25 radios respond to bad data packets addressed to them with a retransmission request, an attacker can deliberately send bad packets forcing a specific radio to transmit even if the user is attempting to maintain [[radio silence]].  Such tracking by authorized users is considered a feature of P25, referred to as "presence".<ref>{{Cite web |url=http://www.nationalinterop.com/solutions_p25.html |title=Design Issues for P25 Digital{{!}} National Interop<!-- Bot generated title --> |access-date=2011-08-15 |archive-url=https://web.archive.org/web/20110714160000/http://www.nationalinterop.com/solutions_p25.html |archive-date=2011-07-14 |url-status=dead }}</ref>

The report's authors concluded by saying "It is reasonable to wonder why this protocol, which was developed over many years and is used for sensitive and critical applications, is so difficult to use and so vulnerable to attack." The authors separately issued a set of recommendations for P25 users to mitigate some of the problems found.<ref>[http://www.net-security.org/article.php?id=1617 P25 security mitigation guide], M. Blaze, et al.</ref> These include disabling the secure/clear switch, using Network Access Codes to segregate clear and encrypted traffic, and compensating for the unreliability of P25 over-the-air rekeying by extending key life.