CryptoDB

Stefan Katzenbeisser

Publications

Year
Venue
Title
2016
CHES
2014
PKC
2014
EPRINT
2014
EPRINT
2012
CHES
2011
CRYPTO
2011
CHES
2008
EPRINT
In the last years, DNA sequencing techniques have advanced to the point that DNA identification and paternity testing has become almost a commodity. Due to the critical nature of DNA related data, this causes substantial privacy issues. In this paper, we introduce cryptographic privacy enhancing protocols that allow to perform the most common DNA-based identity, paternity and ancestry tests and thus implement privacy-enhanced online genealogy services or research projects. In the semi-honest attacker model, the protocols guarantee that no sensitive information about the involved DNA is exposed, and are resilient against common forms of measurement errors during DNA sequencing. The protocols are practical and efficient, both in terms of communication and computation complexity.
2007
EPRINT
Fingerprinting provides a means of tracing unauthorized redistribution of digital data by individually marking each authorized copy with a personalized serial number. In order to prevent a group of users from collectively escaping identification, collusion-secure fingerprinting codes have been proposed. In this paper, we introduce a new construction of a collusion-secure fingerprinting code which is similar to a recent construction by Tardos but achieves shorter code lengths and allows for codes over arbitrary alphabets. For binary alphabets, $n$ users and a false accusation probability of $\eta$, a code length of $m\approx \pi^2 c_0^2\ln(n/\eta)$ is provably sufficient to withstand collusion attacks of at most $c_0$ colluders. This improves Tardos' construction by a factor of $10$. Furthermore, invoking the Central Limit Theorem we show that even a code length of $m\approx \half\pi^2 c_0^2\ln(n/\eta)$ is sufficient in most cases. For $q$-ary alphabets, assuming the restricted digit model, the code size can be further reduced. Numerical results show that a reduction of 35\% is achievable for $q=3$ and 80\% for~$q=10$.
2007
EPRINT
During the last years, large-scale simulations of realistic physical environments which support the interaction of multiple participants over the Internet have become increasingly available and economically viable, most notably in the computer gaming industry. Such systems, commonly called networked virtual environments (NVEs), are usually based on a client-server architecture where for performance reasons and bandwidth restrictions, the simulation is partially delegated to the clients. This inevitable architectural choice renders the simulation vulnerable to attacks against the semantic integrity of the simulation: malicious clients may attempt to compromise the physical and logical rules governing the simulation, or to alter the causality of events a posteriori. In this paper, we initiate the systematic study of semantic integrity in NVEs from a security point of view. We argue that naive policies to enforce semantic integrity involve intolerable network load, and are therefore not practically feasible. We present a new provably secure semantic integrity protocol based on cryptographic primitives which enables the server system to audit the local computations of the clients on demand. Our approach facilitates low network and CPU load, incurs reasonable engineering overhead, and maximally decouples the auditing process from the soft real time constraints of the simulation.
2004
EPRINT
The recent advances in multimedia technology have made the manipulation of digital images, videos or audio files easy. On the one hand the broad availability of these new capabilities enabled numerous new applications. On the other hand, for the same reasons, digital media can easily be forged by almost anyone. To counteract this risk, fragile watermarks were proposed to protect the integrity and authenticity of digital multimedia objects. Traditional watermarking schemes employ non-cryptographic and signal processing oriented techniques, which fail to provide any provable security guarantee against malicious modification attempts. In this paper, we give for the first time a provably secure authentication mechanism for digital multimedia files that is based on both cryptographic signatures and invertible watermarks. While traditional watermarking schemes introduce some small irreversible distortion in the digital content, invertible watermarks can be completely removed from a watermarked work.