@unpublished{2969, author = {{Blömer, Johannes and Brauer, Sascha and Bujna, Kathrin}}, publisher = {{Computing Research Repository}}, title = {{{Hard-Clustering with Gaussian Mixture Models}}}, year = {{2016}}, } @inbook{2970, author = {{Blömer, Johannes and Bujna, Kathrin}}, booktitle = {{Advances in Knowledge Discovery and Data Mining}}, isbn = {{9783319317496}}, issn = {{0302-9743}}, pages = {{296--308}}, publisher = {{Springer International Publishing}}, title = {{{Adaptive Seeding for Gaussian Mixture Models}}}, doi = {{10.1007/978-3-319-31750-2_24}}, year = {{2016}}, } @techreport{2971, author = {{Blömer, Johannes and Günther, Peter}}, publisher = {{Tagungsband des 26. Fraunhofer SIT Smartcard-Workshops}}, title = {{{Effizienz und Sicherheit paarungsbasierter Kryptographie}}}, year = {{2016}}, } @misc{213, author = {{Porzenheim, Laurens}}, publisher = {{Universität Paderborn}}, title = {{{Comparison of different Definitions of Chosen-Ciphertext Security in Encryption schemes}}}, year = {{2016}}, } @misc{214, author = {{Bemmann, Kai Sören}}, publisher = {{Universität Paderborn}}, title = {{{Commitment Schemes - Definitions, Variants, and Security}}}, year = {{2016}}, } @inproceedings{2367, abstract = {{One of the most popular fuzzy clustering techniques is the fuzzy K-means algorithm (also known as fuzzy-c-means or FCM algorithm). In contrast to the K-means and K-median problem, the underlying fuzzy K-means problem has not been studied from a theoretical point of view. In particular, there are no algorithms with approximation guarantees similar to the famous K-means++ algorithm known for the fuzzy K-means problem. This work initiates the study of the fuzzy K-means problem from an algorithmic and complexity theoretic perspective. We show that optimal solutions for the fuzzy K-means problem cannot, in general, be expressed by radicals over the input points. Surprisingly, this already holds for simple inputs in one-dimensional space. Hence, one cannot expect to compute optimal solutions exactly. We give the first (1+eps)-approximation algorithms for the fuzzy K-means problem. First, we present a deterministic approximation algorithm whose runtime is polynomial in N and linear in the dimension D of the input set, given that K is constant, i.e. a polynomial time approximation scheme (PTAS) for fixed K. We achieve this result by showing that for each soft clustering there exists a hard clustering with similar properties. Second, by using techniques known from coreset constructions for the K-means problem, we develop a deterministic approximation algorithm that runs in time almost linear in N but exponential in the dimension D. We complement these results with a randomized algorithm which imposes some natural restrictions on the sought solution and whose runtime is comparable to some of the most efficient approximation algorithms for K-means, i.e. linear in the number of points and the dimension, but exponential in the number of clusters.}}, author = {{Blömer, Johannes and Brauer, Sascha and Bujna, Kathrin}}, booktitle = {{2016 IEEE 16th International Conference on Data Mining (ICDM)}}, isbn = {{9781509054732}}, keywords = {{unsolvability by radicals, clustering, fuzzy k-means, probabilistic method, approximation algorithms, randomized algorithms}}, location = {{Barcelona, Spain}}, pages = {{805--810}}, publisher = {{IEEE}}, title = {{{A Theoretical Analysis of the Fuzzy K-Means Problem}}}, doi = {{10.1109/icdm.2016.0094}}, year = {{2016}}, } @inproceedings{208, abstract = {{This paper presents a new framework for constructing fully CCA-secure predicate encryption schemes from pair encoding schemes. Our construction is the first in the context of predicate encryption which uses the technique of well-formedness proofs known from public key encryption. The resulting constructions are simpler and more efficient compared to the schemes achieved using known generic transformations from CPA-secure to CCA-secure schemes. The reduction costs of our framework are comparable to the reduction costs of the underlying CPA-secure framework. We achieve this last result by applying the dual system encryption methodology in a novel way.}}, author = {{Blömer, Johannes and Liske, Gennadij}}, booktitle = {{Proceedings of the CT-RSA 2016}}, pages = {{431--447}}, title = {{{Construction of Fully CCA-Secure Predicate Encryptions from Pair Encoding Schemes}}}, doi = {{10.1007/978-3-319-29485-8_25}}, year = {{2016}}, } @phdthesis{167, author = {{Günther, Peter}}, publisher = {{Universität Paderborn}}, title = {{{Physical attacks on pairing-based cryptography}}}, year = {{2016}}, } @misc{146, author = {{Hamm, Julian}}, publisher = {{Universität Paderborn}}, title = {{{Symmetric Anonymous Credentials with Protocols for Relations on Attributes}}}, year = {{2016}}, } @misc{152, author = {{Dallmeier, Fynn}}, publisher = {{Universität Paderborn}}, title = {{{Short Randomizable Aggregatable Signatures: Constructions and Security Analysis}}}, year = {{2016}}, } @inbook{2978, author = {{Blömer, Johannes and Bujna, Kathrin}}, booktitle = {{Advances in Knowledge Discovery and Data Mining}}, isbn = {{9783319317496}}, issn = {{0302-9743}}, pages = {{296--308}}, publisher = {{Springer International Publishing}}, title = {{{Adaptive Seeding for Gaussian Mixture Models}}}, doi = {{10.1007/978-3-319-31750-2_24}}, year = {{2016}}, } @inproceedings{253, abstract = {{Group signatures, introduced by Chaum and van Heyst [15], are an important primitive in cryptography. In group signature schemes every group member can anonymously sign messages on behalf of the group. In case of disputes a dedicated opening manager is able to trace signatures - he can extract the identity of the producer of a given signature. A formal model for static group signatures schemes and their security is defined by Bellare, Micciancio, and Warinschi [4], the case of dynamic groups is considered by Bellare, Shi, and Zhang [5]. Both models define group signature schemes with a single opening manager. The main difference between these models is that the number of group members in static schemes is fixed, while in dynamic schemes group members can join the group over time.}}, author = {{Blömer, Johannes and Juhnke, Jakob and Löken, Nils}}, booktitle = {{Proceedings of the Sixth International Conference on Mathematical Aspects of Computer and Information Sciences (MACIS)}}, pages = {{166--180}}, title = {{{Short Group Signatures with Distributed Traceability}}}, doi = {{10.1007/978-3-319-32859-1_14}}, year = {{2015}}, } @misc{286, author = {{Kalde, Benedikt}}, publisher = {{Universität Paderborn}}, title = {{{Implementierung eines hybriden Verschlüsselungsverfahrens nach Cramer und Shoup}}}, year = {{2015}}, } @misc{2865, author = {{Strotmann, Daniela}}, title = {{{Singulärwertzerlegung für μ-ähnliche Bregman-Divergenzen}}}, year = {{2015}}, } @misc{261, author = {{Eisenhofer, Thorsten}}, publisher = {{Universität Paderborn}}, title = {{{Protokolle zur authentifizierten Schüsselvereinbarung}}}, year = {{2015}}, } @misc{321, author = {{Eidens, Fabian}}, publisher = {{Universität Paderborn}}, title = {{{Anonymous credential system based on q-Strong Diffie-Hellman Assumption}}}, year = {{2015}}, } @inproceedings{322, abstract = {{Reputation systems are used to compute and publish reputation scores for services or products. We consider reputation systems where users are allowed to rate products that they purchased previously. To obtain trustworthy reputations, they are allowed to rate these products only once. As long as users rate products once, they stay anonymous. Everybody is able to detect users deviating from the rate-products-only-once policy and the anonymity of such dishonest users can be revoked by a system manager. In this paper we present formal models for such reputation systems and their security. Based on group signatures presented by Boneh, Boyen, and Shacham we design an efficient reputation system that meets all our requirements.}}, author = {{Blömer, Johannes and Juhnke, Jakob and Kolb, Christina}}, booktitle = {{Proceedings of the 18th International Conference on Financial Cryptography and Data Security (FC)}}, pages = {{478----488}}, title = {{{Anonymous and Publicly Linkable Reputation Systems}}}, doi = {{10.1007/978-3-662-47854-7_29}}, year = {{2015}}, } @misc{325, author = {{Löken, Nils}}, publisher = {{Universität Paderborn}}, title = {{{A Group Signature Scheme with Distributed Group Management - An Application of Threshold Encryption}}}, year = {{2015}}, } @misc{326, author = {{Heihoff, Frederic}}, publisher = {{Universität Paderborn}}, title = {{{A group signature scheme based on the LSRW assumption}}}, year = {{2015}}, } @misc{297, author = {{Sosniak, Martin}}, publisher = {{Universität Paderborn}}, title = {{{Evaluation of Pairing Optimization for Embedded Platforms}}}, year = {{2015}}, }