# Deniable authentication

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{{Short description|Message authentication verifiable only by participants}}
In [cryptography](/source/cryptography), '''deniable authentication''' is [message authentication](/source/message_authentication) between a set of participants where the participants themselves can be confident in the authenticity of the messages, but it cannot be proved to a third party after the event.<ref>{{cite journal |author=Wei-Bin Lee |author2=Chia-Chun Wu |author3=Woei-Jiunn Tsaur |date=17 April 2006 |title=A novel deniable authentication protocol using generalized ElGamal signature scheme |journal=Information Sciences |volume=177 |issue=6 |pages=1376–1381 |doi=10.1016/j.ins.2006.09.020 |url=http://torfone.org/download/nida.pdf |archive-url=https://web.archive.org/web/20160305052737/http://torfone.org/download/nida.pdf |url-status=usurped |archive-date=March 5, 2016 |access-date=21 January 2015 }}</ref><ref>{{cite journal |author=Mario Di Raimondo |author2=Rosario Gennaro |date=28 May 2009 |title=New Approaches for Deniable Authentication |journal=Journal of Cryptology |volume=22 |issue=4 |pages=572–615 |doi=10.1007/s00145-009-9044-3 |citeseerx=10.1.1.59.1917 |s2cid=211210 }} ([https://eprint.iacr.org/2005/046 Download 2005 preprint version])</ref><ref>{{cite journal |author=Jayaprakash Kar |author2=Banshidhar Majhi |date=11 June 2010 |title=A secure Deniable Authentication Protocol based on Bilinear Diffie-Hellman Algorithm |journal=Preprint |url=https://eprint.iacr.org/2010/340 }}</ref>

In practice, deniable authentication between two parties can be achieved through the use of [message authentication code](/source/message_authentication_code)s (MACs) by making sure that if an attacker is able to decrypt the messages, they would also know the MAC key as part of the protocol, and would thus be able to forge authentic-looking messages.<ref>{{cite journal |author=Lein Harn |author2=Chia-Yin Lee |author3=Changlu Lin |author4=Chin-Chen Chang |date=11 June 2011 |title=Fully Deniable Message Authentication Protocols Preserving Confidentiality |journal=The Computer Journal |volume=54 |issue=10 |pages=1688–1699 |url=http://h.web.umkc.edu/harnl/papers/j2011j2..pdf }}</ref> For example, in the [Off-the-Record Messaging](/source/Off-the-Record_Messaging) (OTR) protocol, MAC keys are derived from the asymmetric decryption key through a [cryptographic hash function](/source/cryptographic_hash_function). In addition to that, the OTR protocol also reveals used MAC keys as part of the next message, after they have already been used to authenticate previously received messages, and they are not used again.<ref name=otr>{{cite conference |author=[Nikita Borisov](/source/Nikita_Borisov) |author2=[Ian Goldberg](/source/Ian_Goldberg) |author3=[Eric Brewer](/source/Eric_Brewer_(computer_scientist)) |title=Off-the-Record Communication, or, Why Not to Use PGP |conference=Workshop on Privacy in the Electronic Society 2004 |date=2004-10-28 |url=https://otr.cypherpunks.ca/otr-wpes.pdf |access-date=2007-02-01 }}</ref>

==See also==
* [Deniable encryption](/source/Deniable_encryption)
* [Plausible deniability](/source/Plausible_deniability)
* [Malleability](/source/Malleability_(cryptography))
* [Undeniable signature](/source/Undeniable_signature)

==References==
{{Reflist}}

Category:Cryptographic protocols

{{crypto-stub}}

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Adapted from the Wikipedia article [Deniable authentication](https://en.wikipedia.org/wiki/Deniable_authentication) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Deniable_authentication?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.