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Strengthening public key authentication against key theft

Martin Kleppmann
December 09, 2015

Strengthening public key authentication against key theft

Slides from my talk presented at the 9th International Conference on Passwords (Passwords15), Cambridge, UK, 9 December 2015.
Paper: http://martin.kleppmann.com/papers/mrsa-pass15.pdf
Conference website: http://www.cl.cam.ac.uk/events/passwords2015/


Authentication protocols based on an asymmetric keypair provide strong authentication as long as the private key remains secret, but may fail catastrophically if the private key is lost or stolen. Even when encrypted with a password, stolen key material is susceptible to offline brute-force attacks. In this paper we demonstrate a method for rate-limiting password guesses on stolen key material, without requiring special hardware or changes to servers. By slowing down offline attacks and enabling easy key revocation our algorithm reduces the risk of key compromise, even if a low-entropy password is used.

Martin Kleppmann

December 09, 2015

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  52. 1.  Dan Boneh, Xuhua Ding, Gene Tsudik, and Chi Ming

    Wong: “A Method for Fast Revocation of Public Key Certificates and Security Capabilities,” at 10th USENIX Security Symposium, August 2001. 2.  Mirosław Kutyłowski, Przemysław Kubiak, Michał Tabor, and Daniel Wachnik: “Mediated RSA cryptography specification for additive private key splitting (mRSAA),” IETF Internet Draft, November 2012. https://tools.ietf.org/html/draft-kutylowski-mrsa-algorithm-03 3.  J. Jonsson and B. Kaliski: “Public-Key Cryptography Standards (PKCS) #1: RSA cryptography specifications version 2.1”. Network Working Group RFC 3447, Feb 2003. 4.  Sampath Srinivas, Dirk Balfanz, Eric Tiffany, and Alexei Czeskis: “Universal 2nd factor (U2F) overview”. FIDO Alliance Proposed Standard, May 2015. https://fidoalliance.org/specs/fido-u2f-v1.0-nfc-bt- amendment-20150514/fido-u2f-overview.html 5.  T. Ylonen and C. Lonvick: “The Secure Shell (SSH) authentication protocol”. Network Working Group RFC 4252, Jan 2006.
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