Dynamic Threshold Cryptosystem without Group Manager

In dynamic networks with flexible memberships, group signatures and distributed signatures are an important problem. Dynamic threshold cryptosystems are best suited to realize distributed signatures in dynamic (e.g. meshed) networks. Without a group manager or a trusted third party even more flexible scenarios can be realized. Gennaro et al. showed, it is possible to dynamically increase the size of the signer group, without altering the public key. We extend this idea by removing members from the group, also without changing the public key. This is an important feature for dynamic groups, since it is very common, e.g. in meshed networks that members leave a group. Gennaro et al. used RSA and bi-variate polynomials for their scheme. In contrast, we developed a DL-based scheme that uses ideas from the field of proactive secret sharing (PSS). One advantage of our scheme is the possibility to use elliptic curve cryptography and thereby decrease the communication and computation complexity through a smaller security parameter. Our proposal is an efficient threshold cryptosystem that is able to adapt the group size in both directions. Since it is not possible to realize a non-interactive scheme with the ability to remove members (while the public key stays unchanged), we realized an interactive scheme whose communication efficency is highly optimized to compete with non-interactive schemes. Our contribution also includes a security proof for our threshold scheme

Effect of sparsity-aware time–frequency analysis on dynamic hand gesture classification with radar micro-Doppler signatures

Dynamic hand gesture recognition is of great importance in human-computer interaction. In this study, the authors investigate the effect of sparsity-driven time-frequency analysis on hand gesture classification. The time-frequency spectrogram is first obtained by sparsity-driven time-frequency analysis. Then three empirical micro-Doppler features are extracted from the time-frequency spectrogram and a support vector machine is used to classify six kinds of dynamic hand gestures. The experimental results on measured data demonstrate that, compared to traditional time-frequency analysis techniques, sparsity-driven time-frequency analysis provides improved accuracy and robustness in dynamic hand gesture classification

Feature Representation for Online Signature Verification

Biometrics systems have been used in a wide range of applications and have improved people authentication. Signature verification is one of the most common biometric methods with techniques that employ various specifications of a signature. Recently, deep learning has achieved great success in many fields, such as image, sounds and text processing. In this paper, deep learning method has been used for feature extraction and feature selection.Comment: 10 pages, 10 figures, Submitted to IEEE Transactions on Information Forensics and Securit

Efficient distributed tag-based encryption and its application to group signatures with efficient distributed traceability

In this work, we first formalize the notion of dynamic group signatures with distributed traceability, where the capability to trace signatures is distributed among n managers without requiring any interaction. This ensures that only the participation of all tracing managers permits tracing a signature, which reduces the trust placed in a single tracing manager. The threshold variant follows easily from our definitions and constructions. Our model offers strong security requirements. Our second contribution is a generic construction for the notion which has a concurrent join protocol, meets strong security requirements, and offers efficient traceability, i.e. without requiring tracing managers to produce expensive zero-knowledge proofs for tracing correctness. To dispense with the expensive zero-knowledge proofs required in the tracing, we deploy a distributed tag-based encryption with public verifiability. Finally, we provide some concrete instantiations, which, to the best of our knowledge, are the first efficient provably secure realizations in the standard model simultaneously offering all the aforementioned properties. To realize our constructions efficiently, we construct an efficient distributed (and threshold) tag-based encryption scheme that works in the efficient Type-III asymmetric bilinear groups. Our distributed tag-based encryption scheme yields short ciphertexts (only 1280 bits at 128-bit security), and is secure under an existing variant of the standard decisional linear assumption. Our tag-based encryption scheme is of independent interest and is useful for many applications beyond the scope of this paper. As a special case of our distributed tag-based encryption scheme, we get an efficient tag-based encryption scheme in Type-III asymmetric bilinear groups that is secure in the standard model