International Association for Cryptologic Research

International Association
for Cryptologic Research

CryptoDB

Jörg Schwenk

Publications

Year
Venue
Title
2014
PKC
2014
EPRINT
2012
CRYPTO
2010
ASIACRYPT
2009
ASIACRYPT
2008
EPRINT
Universally Composable Security Analysis of TLS---Secure Sessions with Handshake and Record Layer Protocols
We present a security analysis of the complete TLS protocol in the Universal Composable security framework. This analysis evaluates the composition of key exchange functionalities realized by the TLS handshake with the message transmission of the TLS record layer to emulate secure communication sessions and is based on the adaption of the secure channel model from Canetti and Krawczyk to the setting where peer identities are not necessarily known prior the protocol invocation and may remain undisclosed. Our analysis shows that TLS, including the Diffie-Hellman and key transport suites in the uni-directional and bi-directional models of authentication, securely emulates secure communication sessions.
2008
EPRINT
The Generic Hardness of Subset Membership Problems under the Factoring Assumption
Tibor Jager Jörg Schwenk
We analyze a large class of subset membership problems related to integer factorization. We show that there is no algorithm solving these problems efficiently without exploiting properties of the given representation of ring elements, unless factoring integers is easy. Our results imply that problems with high relevance for a large number of cryptographic applications, such as the quadratic residuosity and the subgroup decision problems, are generically equivalent to factoring.
2007
EPRINT
Provably Secure Framework for Information Aggregation is Sensor Networks
Mark Manulis Jörg Schwenk
Information aggregation is an important operation in wireless sensor networks executed for the purpose of monitoring and reporting of the environmental data. Due to the performance constraints of sensor nodes the in-network form of the aggregation is especially attractive since it allows to save expensive resources during the frequent network queries. Easy accessibility of networks and nodes and almost no physical protection against corruptions arise high challenges on the security of the aggregation process. Especially, protection against attacks aiming to falsify the aggregated result is considered to be of prime importance. In this paper we propose a novel security model for the aggregation process based on the well-established cryptographic techniques, focusing on the scenario with the single aggregator node. In order to show soundness and feasibility of our definitions we describe a generic practical approach that achieves security against node corruptions during the aggregation process in a provable cryptographic way based solely on the symmetric cryptographic primitives. To the best of our knowledge this is the first paper which aims to combine the paradigm of provable security in the cryptographic sense with the task of information aggregation in WSNs.
2006
EPRINT
Linkable Democratic Group Signatures
In a variety of group-oriented applications cryptographic primitives like group signatures or ring signatures are valuable methods to achieve anonymity of group members. However, in their classical form, these schemes cannot be deployed for applications that simultaneously require (i) to avoid centralized management authority like group manager and (ii) the signer to be anonymous only against non-members while group members have rights to trace and identify the signer. The idea of recently introduced {\it democratic group signatures} is to provide these properties. Based on this idea we introduce a group-oriented signature scheme that allows the group members to trace the identity of any other group member who issued a signature while non-members are only able to link the signatures issued by the same signer without tracing. For this purpose the signature scheme assigns to every group member a unique pseudonym that can be used by any non-member verifier to communicate with the anonymous signer from the group. We present several group-oriented application scenarios where this kind of linkability is essential. We propose a concrete linkable democratic group signature scheme for two-parties, prove its security in the random oracle model, and describe how to modularly extend it to the multi-party case.
2006
EPRINT
On Security Models and Compilers for Group Key Exchange Protocols
Group key exchange (GKE) protocols can be used to guarantee confidentiality and group authentication in a variety of group applications. The notion of provable security subsumes the existence of an abstract formalization (security model) that considers the environment of the protocol and identifies its security goals. The first security model for GKE protocols was proposed by Bresson, Chevassut, Pointcheval, and Quisquater in 2001, and has been subsequently applied in many security proofs. Their definitions of AKE- and MA-security became meanwhile standard. In this paper we analyze the BCPQ model and some of its later appeared modifications and identify several security risks resulting from the technical construction of this model – the notion of partnering. Consequently, we propose a revised model with extended definitions for AKE- and MA-security capturing, in addition, attacks of malicious protocol participants. Further, we analyze some well-known generic solutions (compilers) for AKE- and MA-security of GKE protocols proposed based on the definitions of the BCPQ model and its variants and identify several limitations resulting from the underlying assumptions. In order to remove these limitations and at the same time to show that our revised security model is in fact practical enough for the construction of reductionist security proofs we describe a modified compiler which provides AKE- and MA-security for any GKE protocol, under standard cryptographic assumptions.
1996
EUROCRYPT