We describe a digital signature scheme in which the public key is fixed but the secret signing key is updated at regular intervals so as to provide a forward security property: compromise of the current secret key does not enable an adversary to forge signatures pertaining to the past. This can be useful to mitigate the damage caused by key exposure without requiring distribution of keys. Our construction uses ideas from the Fiat-Shamir and Ong-Schnorr identification and signature schemes, and is proven to be forward secure based on the hardness of factoring, in the random oracle model. The construction is also quite efficient.

A forward-secure digital signature scheme.

The main efforts of recent years have focused on the problem of set a name securely to public keys, in fact, the scientific community has been gradually adopting the use of systems based in Public Key Infrastructure (PKI) in order to provide security services. However, that systems depend on the existence of a centralized and hierarchical method. This same problem is translated into the management of electronic commerce, which presents a central entity that must issue electronic currency to different users. In 2009, Satoshi Nakamoto creates Bitcoin: a peer-to-peer technology to operate without a central authority or banks. This investigation applies in PKI the same concepts that Nakamoto applied in the electronic commerce, a reengineering and a paradigm shift, a migration from a

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Certificados digitales: de una arquitectura jerárquica y centralizada a una distribuida y descentralizada

In 2009, Gentry first proposed a concrete method for constructing a fully homomorphic encryption (FHE) scheme, which supports arbitrary operations on encrypted data. The construction of the FHE scheme starts from a somewhat homomorphic encryption (SHE) scheme, which only supports limited operations but can be much faster than the FHE scheme. The Gentry’s scheme is based on ideal lattices, and Chen and Nguyen estimated that it needs at least 10,000 lattice dimension to make the FHE scheme secure. In contrast, the security of the SHE scheme can be guaranteed for lower lattice dimensions, depending on the possible operations which are determined by key parameters. The aim of this paper is to classify which key parameters are feasible to be solved. We attack the lattice problem of lower dimensions by practical lattice reduction algorithms, and estimate the key parameters which can be solved in practice.

Sabrina De Capitani di Vimercati

Papers

Public Key Infrastructures, Services and Applications