137 research outputs found
Better Prefix Authentication
We present new schemes for solving prefix authentication and secure relative
timestamping. By casting a new light on antimonotone linking schemes, we
improve upon the state of the art in prefix authentication, and in timestamping
with rounds of bounded length. Our designs can serve as more efficient
alternatives to certificate transparency logs.Comment: 11 pages, 14 figure
MoPS: A Modular Protection Scheme for Long-Term Storage
Current trends in technology, such as cloud computing, allow outsourcing the
storage, backup, and archiving of data. This provides efficiency and
flexibility, but also poses new risks for data security. It in particular
became crucial to develop protection schemes that ensure security even in the
long-term, i.e. beyond the lifetime of keys, certificates, and cryptographic
primitives. However, all current solutions fail to provide optimal performance
for different application scenarios. Thus, in this work, we present MoPS, a
modular protection scheme to ensure authenticity and integrity for data stored
over long periods of time. MoPS does not come with any requirements regarding
the storage architecture and can therefore be used together with existing
archiving or storage systems. It supports a set of techniques which can be
plugged together, combined, and migrated in order to create customized
solutions that fulfill the requirements of different application scenarios in
the best possible way. As a proof of concept we implemented MoPS and provide
performance measurements. Furthermore, our implementation provides additional
features, such as guidance for non-expert users and export functionalities for
external verifiers.Comment: Original Publication (in the same form): ASIACCS 201
Stamp \& Extend -- Instant but Undeniable Timestamping based on Lazy Trees
We present a Stamp\&Extend time-stamping scheme based on linking via modified creation of Schnorr signatures.
The scheme is based on lazy construction of a tree of signatures.
Stamp\&Extend returns a timestamp immediately after the request, unlike the schemes based on the concept of timestamping rounds.
Despite the fact that all timestamps are linearly linked, verification of a timestamp requires a logarithmic number of steps with respect to the chain length.
An extra feature of the scheme is that any attempt to forge a timestamp by the Time Stamping Authority (TSA) results in revealing its secret key, providing an undeniable cryptographic evidence of misbehavior of TSA.
Breaking Stamp\&Extend requires not only breaking Schnorr signatures,
but to some extend also breaking Pedersen commitments
Experimenting with server-aided signatures
This paper explores practical and conceptual implications of using Server-Aided Signatures (SAS). SAS is a signature method that relies on partiallytrusted servers for generating public key signatures for regular users. Besides its two primary goals of 1) aiding small, resource-limited devices in computing heavy-weight (normally expensive) digital signatures and 2) fast certificate revocation, SAS also o#ers signature causality and has some interesting features such as built-in attack detection for users and DoS resistance for servers
New models for efficient authenticated dictionaries
International audienceWe propose models for data authentication which take into account the behavior of the clients who perform queries. Our models reduce the size of the authenticated proof when the frequency of the query corresponding to a given data is higher. Existing models implicitly assume the frequency distribution of queries to be uniform, but in reality, this distribution generally follows Zipf's law. Our models better reflect reality and the communication cost between clients and the server provider is reduced allowing the server to save bandwidth. The obtained gain on the average proof size compared to existing schemes depends on the parameter of Zipf law. The greater the parameter, the greater the gain. When the frequency distribution follows a perfect Zipf's law, we obtain a gain that can reach 26%. Experiments show the existence of applications for which Zipf parameter is greater than 1, leading to even higher gains
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