Enhancing ZRTP by using Computational Puzzles

Abstract: In this paper we present and discuss a new approach for securing multimedia communication, which is based on three innovations. The first innovation is the integration of a challenge-response scheme for enhancing the Diffie-Hellman based ZRTP protocol. When being called, a callee must present the result of a computational puzzle (a "token") within a short amount of time. A Man-in-the-Middle (MitM) would not be able to compute such a token within the required time, and thus fail to get into the media path. The scheme works best in situations when ZRTP is most vulnerable to so-called Mafia Attacks, i.e., if both caller and callee do not know each other. The second innovation complements the first one on those occasions where the above scheme may fail. The call is delayed for a certain amount of time which depends on the agreed session key. Since during a MitM attack two different keys (and thus waiting times) exist, caller and callee would not start their call at the ...

• Type: Journal
• Year: 2008
• Where: JUCS
• Authors: Helmut Hlavacs, Wilfried N. Gansterer, Hannes Schabauer, Joachim Zottl, Martin Petraschek, Thomas Hoeher, Oliver Jung
• Keywords: Challenge-response Scheme, Computational Puzzle, Innovation, JUCS 2008