Ghost trace on the wire? Using key evidence for informed decisions

Diana A. Vasile, Martin Kleppmann, Daniel R. Thomas, Alastair R. Beresford

Research output: Chapter in Book/Report/Conference proceedingConference contribution book

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Modern smartphone messaging apps now use end-to-end encryption to provide authenticity, integrity and confidentiality. Consequently, the preferred strategy for wiretapping such apps is to insert a ghost user by compromising the platform's public key infrastructure. The use of warning messages alone is not a good defence against a ghost user attack since users change smartphones, and therefore keys, regularly, leading to a multitude of warning messages which are overwhelmingly false positives. Consequently, these false positives discourage users from viewing warning messages as evidence of a ghost user attack. To address this problem, we propose collecting evidence from a variety of sources, including direct communication between smartphones over local networks and CONIKS, to reduce the number of false positives and increase confidence in key validity. When there is enough confidence to suggest a ghost user attack has taken place, we can then supply the user with evidence to help them make a more informed decision.
Original languageEnglish
Title of host publication27th International Workshop on Security Protocols
Place of PublicationCambridge
Number of pages12
Publication statusPublished - 24 Jun 2019
Event27th International Workshop on Security Protocols - Trinity College, Cambridge, United Kingdom
Duration: 10 Apr 201912 Apr 2019


Conference27th International Workshop on Security Protocols
Abbreviated titleSPW
Country/TerritoryUnited Kingdom
Internet address


  • trust establishment
  • public key evidence
  • end-to-end encryption
  • secure messaging
  • security usability
  • informed consent

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