Paper 2013/234

A Cryptographic Analysis of OPACITY

Özgür Dagdelen, Marc Fischlin, Tommaso Gagliardoni, Giorgia Azzurra Marson, Arno Mittelbach, and Cristina Onete


We take a closer look at the Open Protocol for Access Control, Identification, and Ticketing with privacY (OPACITY). This Diffie--Hellman-based protocol is supposed to provide a secure and privacy-friendly key establishment for contactless environments. It is promoted by the US Department of Defense and meanwhile available in several standards such as ISO/IEC 24727-6 and ANSI 504-1. To the best of our knowledge, so far no detailed cryptographic analysis has been publicly available. Thus, we investigate in how far the common security properties for authenticated key exchange and impersonation resistance, as well as privacy-related properties like untraceability and deniability, are met. OPACITY is not a single protocol but, in fact, a suite consisting of two protocols, one called Zero-Key Management (ZKM) and the other one named Fully Secrecy (FS). Our results indicate that the ZKM version does not achieve even very basic security guarantees. The FS protocol, on the other hand, provides a decent level of security for key establishment. Yet, our results show that the persistent-binding steps, for re-establishing previous connections, conflict with fundamental privacy properties.

Available format(s)
Cryptographic protocols
Publication info
Published elsewhere. Unknown where it was published
OPACITYkey exchangeprivacysecurity analysis
Contact author(s)
arno mittelbach @ cased de
2013-04-29: received
Short URL
Creative Commons Attribution


      author = {Özgür Dagdelen and Marc Fischlin and Tommaso Gagliardoni and Giorgia Azzurra Marson and Arno Mittelbach and Cristina Onete},
      title = {A Cryptographic Analysis of OPACITY},
      howpublished = {Cryptology ePrint Archive, Paper 2013/234},
      year = {2013},
      note = {\url{}},
      url = {}
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