Rickia wasmannii (Laboulbeniales) influences the water consumption of Myrmica scabrinodis

24 - Social insect host-microbe interactions, Poste

UC Commitments for Modular Protocol Design and Applications to Revocation and Attribute Tokens

Complex cryptographic protocols are often designed from simple cryptographic primitives, such as signature schemes, encryption schemes, verifiable random functions, and zero-knowledge proofs, by bridging between them with commitments to some of their inputs and outputs. Unfortunately, the known universally composable (UC) functionalities for commitments and the cryptographic primitives mentioned above do not allow such constructions of higher-level protocols as hybrid protocols. Therefore, protocol designers typically resort to primitives with property-based definitions, often resulting in complex monolithic security proofs that are prone to mistakes and hard to verify. We address this gap by presenting a UC functionality for non-interactive commitments that enables modular constructions of complex protocols within the UC framework. We also show how the new functionality can be used to construct hybrid protocols that combine different UC functionalities and use commitments to ensure that the same inputs are provided to different functionalities. We further provide UC functionalities for attribute tokens and revocation that can be used as building blocks together with our UC commitments. As an example of building a complex system from these new UC building blocks, we provide a construction (a hybrid protocol) of anonymous attribute tokens with revocation. Unlike existing accumulator-based schemes, our scheme allows one to accumulate several revocation lists into a single commitment value and to hide the revocation status of a user from other users and verifiers

Universally Composable Direct Anonymous Attestation

Direct Anonymous Attestation (DAA) is one of the most complex cryptographic algorithms that has been deployed in practice. In spite of this, and the long body of work on the subject, there is still no fully satisfactory security definition for DAA. This was already acknowledged by Bernard et al. (IJIC\u2713) who showed that in existing models even fully insecure protocols may be deemed secure. Bernard et al. therefore proposed an extensive set of security games, which however aimed only at a simplified setting, termed pre-DAA. In pre-DAA the host platform that runs the TPM is assumed to be trusted too. Consequently, their notion does not guarantee any security if the TPM is embedded in a potentially corrupt host, which is a significant restriction. In this paper, we give a comprehensive security definition for full DAA in the form of an ideal functionality in the Universal Composability model. Our definition considers the host and TPM to be individual entities that can be in different corruption states. None of the existing DAA schemes immediately satisfies our strong security notion, and we therefore also propose a realization that is based on a DAA scheme supported by the TPM 2.0 standard and rigorously prove it secure in our model

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

DRE-ip : A Verifiable E-Voting Scheme without Tallying Authorities

Nearly all verifiable e-voting schemes require trustworthy authorities to perform the tallying operations. An exception is the DRE-i system which removes this requirement by pre-computing all encrypted ballots before the election using random factors that will later cancel out and allow the public to verify the tally after the election. While the removal of tallying authorities significantly simplifies election management, the pre-computation of ballots necessitates secure ballot storage, as leakage of precomputed ballots endangers voter privacy. In this paper, we address this problem and propose DRE-ip (DRE-i with enhanced privacy). Adopting a different design strategy, DRE-ip is able to encrypt ballots in real time in such a way that the election tally can be publicly verified without decrypting the cast ballots. As a result, DRE-ip achieves end-to-end verifiability without tallying authorities, similar to DRE-i, but with a significantly stronger guarantee on voter privacy. In the event that the voting machine is fully compromised, the assurance on tallying integrity remains intact and the information leakage is limited to the minimum: only the partial tally at the time of compromise is leaked

Short structure-preserving signatures

© Springer International Publishing Switzerland 2016. We construct a new structure-preserving signature scheme in the efficient Type-III asymmetric bilinear group setting with signatures shorter than all existing schemes. Our signatures consist of 3 group elements from the first source group and therefore they are shorter than those of existing schemes as existing ones have at least one component in the second source group whose elements bit size is at least double that of their first group counterparts. Besides enjoying short signatures, our scheme is fully re-randomizable which is a useful property for many applications. Our result also consti- tutes a proof that the impossibility of unilateral structure-preserving signatures in the Type-III setting result of Abe et al. (Crypto 2011) does not apply to constructions in which the message space is dual in both source groups. Besides checking the well-formedness of the message, verifying a signature in our scheme requires checking 2 Pairing Product Equations (PPE) and require the evaluation of only 5 pairings in total which matches the best existing scheme and outperforms many other existing ones. We give some examples of how using our scheme instead of existing ones improves the efficiency of some existing cryptographic pro- tocols such as direct anonymous attestation and group signature related constructions

Improving Practical UC-Secure Commitments based on the DDH Assumption

At Eurocrypt 2011, Lindell presented practical static and adaptively UC-secure commitment schemes based on the DDH assumption. Later, Blazy {\etal} (at ACNS 2013) improved the efficiency of the Lindell\u27s commitment schemes. In this paper, we present static and adaptively UC-secure commitment schemes based on the same assumption and further improve the communication and computational complexity, as well as the size of the common reference string

Public cloud data auditing with practical key update and zero knowledge privacy

Data integrity is extremely important for cloud based storage services, where cloud users no longer have physical possession of their outsourced files. A number of data auditing mechanisms have been proposed to solve this problem. However, how to update a cloud user\u27s private auditing key (as well as the authenticators those keys are associated with) without the user\u27s re-possession of the data remains an open problem. In this paper, we propose a key-updating and authenticator-evolving mechanism with zero-knowledge privacy of the stored files for secure cloud data auditing, which incorporates zero knowledge proof systems, proxy re-signatures and homomorphic linear authenticators. We instantiate our proposal with the state-of-the-art Shacham-Waters auditing scheme. When the cloud user needs to update his key, instead of downloading the entire file and re-generating all the authenticators, the user can just download and update the authenticators. This approach dramatically reduces the communication and computation cost while maintaining the desirable security. We formalize the security model of zero knowledge data privacy for auditing schemes in the key-updating context and prove the soundness and zero-knowledge privacy of the proposed construction. Finally, we analyze the complexity of communication, computation and storage costs of the improved protocol which demonstrates the practicality of the proposal