School of Computing - Research - Working Papers - 2009


Working Papers for 2009



CA-0109:
The security of Lee and Chang's t-out-of-n lottery protocol
David Gray and Caroline Sheedy

We show that Lee and Chang's t-out-of-n lottery protocol fails to live up to its stated security goals and is subject to a number of simple attacks. We also discuss the definition of public verifiability and show that Lee and Chang's definition is too weak for realistic lottery protocols.

CA-0209:
Anonymous Key Issuing using Blind Identity-Based Encryption
Caroline Sheedy and David Gray

In identity-based encryption (IBE) schemes, a user obtains a private key upon the execution of a key extraction protocol. With standard IBE, the identity string that is passed to a key generation centre (KGC) is visible. Recent work introduced the notion of blinding the identity string, resulting in a private key generation protocol which obscures the identity string from a KGC, known as blind IBE. We present the construction of a partially-blind IBE scheme, along with relevant security definitions. Anonymous key issuing (AKI) has are two seemingly conflicting requirements: a user's identity must not be leaked to the key generation centre (KGC), and once authenticated, the user must be able to retrieve her private key. The objective is to enhance a user's privacy by preventing the KGC from learning the identity associated with a key request. We present a construction of an AKI scheme using blind IBE. We propose using it to mitigate the key escrow problem, and highlight other advantages of our scheme over existing schemes.

CA-0309:
E-Voting: a new approach using Double-Blind Identity-based Encryption
Caroline Sheedy and David Gray

We present a novel approach to e-voting for elections, based on a new cryptographic construction, double-blind identity based encryption (IBE). In standard IBE, the identity string that is passed to a key generation centre (KGC) during the key extraction phase is visible to the KGC. Recent work introduced the notion of blinding the identity string, resulting in a private key generation protocol which obscures the identity string from a KGC. A double-blind IBE scheme is an extension of blind IBE schemes. It allows a user to construct an identity string that is partially obscured, with certain elements visible to the KGC while enabling the KGC to add elements to the user constructed string which are obscured from the user. The contribution of this paper is a new protocol for e-voting using double-blind IBE that adheres to conventional security criteria for e-voting schemes. Our protocol provides end-to-end verifiability. We also contribute a plaintext voter receipt and an audit trail, using receipts.