Paper 2016/221

Post-Compromise Security

Katriel Cohn-Gordon, Cas Cremers, and Luke Garratt


In this work we study communication with a party whose secrets have already been compromised. At first sight, it may seem impossible to provide any type of security in this scenario. However, under some conditions, practically relevant guarantees can still be achieved. We call such guarantees ``post-compromise security''. We provide the first informal and formal definitions for post-compromise security, and show that it can be achieved in several scenarios. At a technical level, we instantiate our informal definitions in the setting of authenticated key exchange (AKE) protocols, and develop two new strong security models for two different threat models. We show that both of these security models can be satisfied, by proposing two concrete protocol constructions and proving they are secure in the models. Our work leads to crucial insights on how post-compromise security can (and cannot) be achieved, paving the way for applications in other domains.

Note: See changelog in the appendix for the difference between versions.

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Publication info
Published elsewhere. Minor revision. 2016 IEEE 29th Computer Security Foundations Symposium (CSF)
Post-Compromise SecuritySecurity ProtocolsKey ExchangeRatchetingFuture SecrecyThreat Models
Contact author(s)
cremers @ cispa saarland
2019-10-16: last of 4 revisions
2016-02-29: received
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      author = {Katriel Cohn-Gordon and Cas Cremers and Luke Garratt},
      title = {Post-Compromise Security},
      howpublished = {Cryptology ePrint Archive, Paper 2016/221},
      year = {2016},
      doi = {10.1109/CSF.2016.19},
      note = {\url{}},
      url = {}
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