238129
Parallel Key-Insulated Public Key Encryption Without Random Oracles
Key-insulated cryptography is a crucial technique for protecting private keys. To strengthen the security of key-insulated protocols, Hanaoka, Hanaoka and Imai recently introduced the idea of parallel key-insulated encryption (PKIE) where distinct physically-secure devices (called helpers) are independently used in key updates. Their motivation was to reduce the risk of exposure for helpers by decreasing the frequency of their connections to insecure environments. Hanaoka et al. showed that it was non-trivial to achieve a PKIE scheme fitting their model and proposed a construction based on the Boneh-Franklin identity-based encryption (IBE) scheme. The security of their system was only analyzed in the idealized random oracle model. In this paper, we provide a fairly efficient scheme which is secure in the standard model (i.e. without random oracles). To do so, we first show the existence of a relation between PKIE and the notion of aggregate signatures (AS) suggested by Boneh et al. We then describe our random oracle-free construction using bilinear maps. Thus, our contributions are both on the concrete side, namely the first realization of parallel key-insulated encryption without the random oracle idealization, and on the conceptual side revealing the relationships between two seemingly unrelated primitives.
1040577
Observability Analysis - Detecting When Improved Cryptosystems Fail
In this paper we show that, paradoxically, what looks like a "universal improvement" or a "straight-forward improvement" which enables better security and better reliability on a theoretical level, may in fact, within certain operational contexts, introduce new exposures and attacks, resulting in a weaker operational cryptosystem. We demonstrate a number of such dangerous "improvements". This implies that careful considerations should be given to the fact that an implemented cryptosystem exists within certain operational environments (which may enable certain types of tampering and other observed information channels via faults, side-channel attacks or behavior of system operators). We use our case studies to draw conclusions about certain investigations required in studying implementations and suggested improvements of cryptosystems; looking at them in the context of their operating environments (combined with their potential adversarial settings). We call these investigations observability analysis.
16761632
Efficient Intrusion-Resilient Signatures Without Random Oracles
Intrusion-resilient signatures are key-evolving protocols that extend the concepts of forward-secure and key-insulated signatures. As in the latter schemes, time is divided into distinct periods where private keys are periodically updated while public keys remain fixed. Private keys are stored in both a user and a base; signature operations are performed by the user while the base is involved in periodic updates. Such a system remains secure after arbitrarily many compromises of both modules as long as break-ins are not simultaneous. Besides, when they simultaneously occur within some time period, past periods remain safe. In this work, we propose the first intrusion-resilient signature in the standard model (i.e. without random oracles) which provides both short signatures and at most log-squared private storage in the number of time periods.
34081065
Connectivity Properties in Random Regular Graphs with Edge Faults
We introduce a new model of random graphs, that of random regular graphs with edge faults (which we denote by ), obtained by selecting the edges of a random member of the set of all regular graphs of degree r independently and with probability p. We can thus represent a communication network in which the links fail independently and with probability f =1-p. In order to deal with this new model, we extend the notion of configurations and the translation lemma between configurations and random regular graphs provided by B. Bollobas, by introducing the concept of random configurations, to account for edge faults, and by providing an extended translation lemma between random configurations and graphs. We investigate important connectivity properties of by estimating the ranges of r, f for which, with high probability, graphs a) are highly connected b) become disconnected and c) admit a giant connected component of small diameter.
6385041
Maintenance of a minimum spanning forest in a dynamic planar graph
Abstract : We give efficient algorithms for maintaining a minimum spanning forest of a planar graph subject to on-line modifications. The modifications supported include changes in the edge weights, and insertion and deletion of edges and vertices. To implement the algorithms, we develop a data structure called an edge-ordered dynamic tree, which is a variant of the dynamic tree data structure of Sleator and Tarjan. Using this data structure, our algorithms run in O(log n) time per operation and O(n) space. The algorithms can be used to maintain the connected components of a dynamic planar graph in O(log n) time per operation.