Selfie: reflections on TLS 1.3 with PSK

Nir Drucker, Shay Gueron

Research output: Contribution to journalArticlepeer-review


TLS 1.3 allows two parties to establish a shared session key from an out-of-band agreed pre-shared key (PSK). The PSK is used to mutually authenticate the parties, under the assumption that it is not shared with others. This allows the parties to skip the certificate verification steps, saving bandwidth, communication rounds, and latency. In this paper, we identify a vulnerability in this specific TLS 1.3 option by showing a new “reflection attack” that we call “Selfie.” This attack uses the fact that TLS does not mandate explicit authentication of the server and the client, and leverages it to break the protocol’s mutual authentication property. We explain the root cause of this TLS 1.3 vulnerability, provide a fully detailed demonstration of a Selfie attack using the TLS implementation of OpenSSL, and propose mitigation. The Selfie attack is the first attack on TLS 1.3 after its official release in 2018. It is surprising because it uncovers an interesting gap in the existing TLS 1.3 models that the security proofs rely on. We explain the gap in these model assumptions and show how it affects the proofs in this case.

Original languageEnglish
Pages (from-to)1-18
JournalJournal of Cryptology
Issue number3
StatePublished - Jul 2021

Bibliographical note

Funding Information:
This research was supported by: The Israel Science Foundation (Grant No. 1018/ 16); The BIU Center for Research in Applied Cryptography and Cyber Security, in conjunction with the Israel National Cyber Bureau in the Prime Minister’s Office; the Center for Cyber Law & Policy at the University of Haifa, in conjunction with the Israel National Cyber Directorate in the Prime Minister’s Office.

Publisher Copyright:
© 2021, The Author(s), under exclusive licence to International Association for Cryptologic Research.


  • Network security
  • Reflection attack
  • Selfie attack
  • TLS 1.3

ASJC Scopus subject areas

  • Software
  • Computer Science Applications
  • Applied Mathematics


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