Abstract. We introduce a short signature scheme based on the Computational Diffie-Hellman assumption on certain elliptic and hyper-elliptic curves. The signature length is half the size of a DSA signature for a similar level of security. Our short signature scheme is designed for systems where signatures are typed in by a human or signatures are sent over a low-bandwidth channel. 1

In the Outsourced Database (ODB) model, organizations outsource their data management needs to an external service provider. The service provider hosts clients' databases and offers seamless mechanisms to create, store, update and access (query) their databases. This model introduces several research issues related to data security. One of the core security requirements is providing efficient mechanisms to ensure data integrity and authenticity while incurring minimal computation and bandwidth overhead. In this work, we investigate the problem of ensuring data integrity and suggest secure and practical schemes that help facilitate authentication of query replies. We explore the applicability of popular digital signature schemes (RSA and DSA) as well as a recently proposed scheme due to Boneh et al. [1] and present their performance measurements.

a short signature scheme (BLS scheme) using bilinear pairing on certain elliptic and hyperelliptic curves. Subsequently numerous cryptographic schemes based on BLS signature scheme were proposed. BLS short signature needs a special hash function [6, 1, 8]. This hash function is probabilistic and generally inefficient. In this paper, we propose a new short signature scheme from the bilinear pairings that unlike BLS, uses general cryptographic hash functions such as SHA-1 or MD5, and does not require special hash functions. Furthermore, the scheme requires less pairing operations than BLS scheme and so is more efficient than BLS scheme. We use this signature scheme to construct a ring signature scheme and a new method for delegation. We give the exact security proofs for the new signature scheme and the ring signature scheme in the random oracle model. Keywords: Short signature, Bilinear pairings, ID-based cryptography, Ring signature, Proxy signature

We introduce the notion of certificate-based encryption. In this model, a certificate -- or, more generally, a signature -- acts not only as a certificate but also as a decryption key. To decrypt a message, a keyholder needs both its secret key and an up-to-date certificate from its CA (or a signature from an authorizer). Certificate-based encryption combines the best aspects of identity-based encryption (implicit certification) and public key encryption (no escrow). We demonstrate how certificate-based encryption can be used to construct an e#cient PKI requiring less infrastructure than previous proposals, including Micali's Novomodo, Naor-Nissim and Aiello-Lodha-Ostrovsky.

An aggregate signature scheme (recently proposed by Boneh, Gentry, Lynn, and Shacham) is a method for combining n signatures from n different signers on n different messages into one signature of unit length. We propose sequential aggregate signatures, inwhichthesetof signers is ordered. The aggregate signature is computed by having each signer, in turn, add his signature to it. We show how to realize this in such a way that the size of the aggregate signature is independent of n. This makes sequential aggregate signatures a natural primitive for certificate chains, whose length can be reduced by aggregating all signatures in a chain. We give a construction in the random oracle model based on families of certified trapdoor permutations, and show how to instantiate our scheme based on RSA. 1

We introduce Ad hoc Anonymous Identification schemes, a new multi-user cryptographic primitive that allows participants from a user population to form ad-hoc groups, and then prove membership anonymously in such groups. Our schemes are based on the notion of accumulator with one-way domain, a natural extension of cryptographic accumulators we introduce in this work. We provide a formal model for Ad hoc Anonymous Identification schemes and design secure such schemes both generically (based on any accumulator with one-way domain) and for a specific e#cient implementation of such an accumulator based on the Strong RSA Assumption. A salient feature of our approach is that all the identification protocols take time independent of the size of the ad-hoc group. All our schemes and notions can be generally and efficiently amended so that they allow the recovery of the signer's identity by an authority, if the latter is desired. Using

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The Border Gateway Protocol (BGP) is the de facto interdomain routing protocol of the Internet. Although the performance of BGP has been historically acceptable, there are continuing concerns about its ability to meet the needs of the rapidly evolving Internet. A major limitation of BGP is its failure to adequately address security. Recent outages and security analyses clearly indicate that the Internet routing infrastructure is highly vulnerable. Moreover, the design and ubiquity of BGP has frustrated past efforts at securing interdomain routing. This paper considers the vulnerabilities currently existing within interdomain routing and surveys works relating to BGP security. The limitations and advantages of proposed solutions are explored, and the systemic and operational implications of their designs considered. We note that no current solution has yet found an adequate balance between comprehensive security and deployment cost. This work calls not only for the application of ideas described within this paper, but also for further investigation into the problems and solutions of BGP security.

In this paper we propose and analyze a method for proofs of actual query execution in an outsourced database framework, in which a client outsources its data management needs to a specialized provider. The solution is not limited to simple selection predicate queries but handles arbitrary query types. While this work focuses mainly on read-only, computeintensive (e.g. data-mining) queries, it also provides preliminary mechanisms for handling data updates (at additional costs). We introduce query execution proofs; for each executed batch of queries the database service provider is required to provide a strong cryptographic proof that provides assurance that the queries were actually executed correctly over their entire target data set. We implement a proof of concept and present experimental results in a real-world data mining application, proving the deployment feasibility of our solution. We analyze the solution and show that its overheads are reasonable and are far outweighed by the added security benefits. For example an assurance level of over 95% can be achieved with less than 25% execution time overhead.

Ring signatures, first introduced by Rivest, Shamir, and Tauman, enable a user to sign a message so that a ring of possible signers (of which the user is a member) is identified, without revealing exactly which member of that ring actually generated the signature. In contrast to group signatures, ring signatures are completely “ad-hoc ” and do not require any central authority or coordination among the various users (indeed, users do not even need to be aware of each other); furthermore, ring signature schemes grant users fine-grained control over the level of anonymity associated with any particular signature. This paper has two main areas of focus. First, we examine previous definitions of security for ring signature schemes and suggest that most of these prior definitions are too weak, in the sense that they do not take into account certain realistic attacks. We propose new definitions of anonymity and unforgeability which address these threats, and give separation results proving that our new notions are strictly stronger than previous ones. Second, we show the first constructions of ring signature schemes in the standard model. One scheme is based on generic assumptions and satisfies our strongest definitions of security. Two additional schemes are more efficient, but achieve weaker security guarantees and more limited functionality. 1