franconian.net talks

Adopting the Noise Key Exchange in Tox

franconian.net
Tobias "Tobi" Buchberger
Tox [0] is a free and open source peer-to-peer instant messaging protocol and implementation, that aims to provide secure messaging. It’s intended as an end-to-end encrypted (E2EE) and distributed Skype replacement. Tox’ cryptography is based on the NaCl library from Daniel J. Bernstein [1]. The cryptographic primitives for the key exchange (X25519), authentication (Poly1305) and symmetric encryption (XSalsa20) are state of the art peer-reviewed algorithms. Unfortunately Tox’ authenticated key exchange (AKE) during Tox’ cryptographic handshake is a "home-brewed" cryptographic protocol (remember: do not roll your own crypto!) and is known to be vulnerable to key compromise impersonation (KCI) attacks [2]. In this talk we will show why this vulnerability is challenging to exploit in practice. However, we will also present a fix to this vulnerability by designing and implementing a new cryptographic Tox handshake with formally-verified security properties.
KCI is a vulnerability of AKE protocols, which in this case could enable an attacker, who compromised the static long-term private X25519 [3] key of a Tox user Alice, to impersonate any other Tox user (with certain assumptions) to Alice ("reverse impersonation"). Furthermore, this would enable this attacker to perform a Man-in-the-Middle (MitM) attack and therefore tampering of exchanged messages. X25519 key pairs, that are necessary for the distributed hash table (DHT), make an actual KCI-attack more complex as suggested in the initial vulnerability report by Jason A. Donenfeld. The Noise Protocol Framework [4] from Trevor Perrin (co-author of Signal [5]) was used to design a new KCI-resistant Tox’ handshake. The Noise Protocol Framework is intended to use by protocol designers to create secure channel protocols based on Diffie-Hellman (DH) key agreement. Noise provides different handshake patterns for different use cases. These patterns define a sequence of DH operations to calculate a shared symmetric session key. The security properties of these patterns are formally verified. These security properties can include forward secrecy, identity hiding and most notably KCI-resistance. A handshake pattern is instantiated by DH functions, cipher functions and hash functions to give a concrete Noise protocol. Such Noise protocols are already used in some applications, like WireGuard VPN [6]. The Noise protocol used in Tox is Noise_IK_25519_ChaChaPoly_SHA512. The Noise-C library from Rhys Weatherley [7] was used to implement the new AKE in c-toxcore [8]. The implementation is currently in proof-of-concept state and will be further improved. In future work, instead of using the Noise-C library, which supports most of Noise’ handshake patterns and all cryptographic primitives, only the Noise protocol used in the Tox handshake will be implemented in c-toxcore. This would remove Noise-C as a dependency (i.e the only other dependency is NaCl/libsodium), reduce source lines of code and therefore reduce the attack surface. Noise also provides functions to further improve security, like session re-keying, which could also be adopted in Tox. Terminology in context of Tox: - Tox is the name of the protocol in general - The implementation of Tox is toxcore - a network library - The clients (using toxcore) have specific names (e.g. qTox [9]) ____ [0] https://tox.chat/ [1] https://nacl.cr.yp.to/ [2] https://github.com/TokTok/c-toxcore/issues/426 [3] https://ed25519.cr.yp.to/ [4] https://noiseprotocol.org/ [5] https://signal.org/docs/ [6] https://www.wireguard.com/ [7] https://rweather.github.io/noise-c/index.html [8] https://github.com/TokTok/c-toxcore [9] https://github.com/qTox/qTox

Additional information

Type Talk
Language English

More sessions

12/27/20
franconian.net talks
Florian Festi
franconian.net
Laser cutters get more and more common in hacker and maker spaces around the world - and rightly so. They are amazing machines that are fast, precise, versatile and easy to use. This talk will get give a quick introduction into laser cutting and will show a few examples what a laser cutter can do.
12/27/20
franconian.net talks
Anthony
franconian.net
An overview of Tox, including the motivation for the project, its benefits, how the protocol works, info on the reference library, and info on some of the clients.
12/28/20
franconian.net talks
franconian.net
From the AFL++ team comes a talk about the core concepts of fuzzing, novel fuzzing research, a library, and parts of fuzzing that can be edited and swapped out.
12/28/20
franconian.net talks
miro
franconian.net
Names of people cannot be invalid.
12/28/20
franconian.net talks
Vanessa
franconian.net
Die Geschichte einer etwas ungewöhnlichen Hausbesetzung im schwäbischen Reutlingen (kein Witz!) und was sich daraus bisher entwickelt hat - zusammen mit einer Idee, wie selbstbestimmtes Wohnen aussehen kann und meinen bisherigen Erfahrungen, was auf unserem Weg hilfreich war.
12/29/20
franconian.net talks
franconian.net
Frauen gelten insbesondere als perfide Zielscheibe von Hass und Hetze im digitalen Diskurs. Wir schauen uns die Dimension der digitalen Gewalt gegen Frauen genauer an. Die Bandbreite unterschiedlicher Erscheinungsformen sowie ihre Strafbarkeit wird vorgestellt. Wir beleuchten die unterschiedlichen Ursachen und zeigen davon ausgehend die daraus entstehenden Probleme und Konsequenzen. Handlungsmöglichkeiten und ein interaktiver Austausch bieten einen aktiven Abschluss.
12/29/20
franconian.net talks
Constantin Ganß
franconian.net
Der Vortrag soll auf "Anti-Corona-Demonstrationen" verbreiteten Antisemitismus aufmerksam machen. Zunächst wird in die zugrunde liegenden antisemitischen Erklärungsmuster und Denkweisen eingeführt. Danach wird Bamberg als "Case-Study" untersucht. Hierbei werden das Demonstrationsfeld und in Bamberg gehaltene Reden analysiert.