International Association for Cryptologic Research

International Association
for Cryptologic Research

CryptoDB

John Malone-Lee

Affiliation: University of Bristol

Publications

Year
Venue
Title
2011
JOFC
2010
JOFC
2008
JOFC
2008
JOFC
2007
PKC
2007
TCC
2006
EPRINT
Identity-Based Encryption Gone Wild
In this paper we introduce a new primitive called identity-based encryption with wildcards, or WIBE for short. It allows to encrypt messages to a whole range of users simultaneously whose identities match a certain pattern. This pattern is defined through a sequence of fixed strings and wildcards, where any string can take the place of a wildcard in a matching identity. Our primitive can be applied to provide an intuitive way to send encrypted email to groups of users in a corporate hierarchy. We propose a full security notion and give efficient implementations meeting this notion under different pairing-related assumptions, both in the random oracle model and in the standard model.
2006
EPRINT
Obfuscation for Cryptographic Purposes
Dennis Hofheinz John Malone-Lee Martijn Stam
An obfuscation O of a function F should satisfy two requirements: firstly, using O it should be possible to evaluate F; secondly, O should not reveal anything about F that cannot be learnt from oracle access to F. Several definitions for obfuscation exist. However, most of them are either too weak for or incompatible with cryptographic applications, or have been shown impossible to achieve, or both. We give a new definition of obfuscation and argue for its reasonability and usefulness. In particular, we show that it is strong enough for cryptographic applications, yet we show that it has the potential for interesting positive results. We illustrate this with the following two results: - If the encryption algorithm of a secure secret-key encryption scheme can be obfuscated according to our definition, then the result is a secure public-key encryption scheme. - A uniformly random point function can be easily obfuscated according to our definition, by simply applying a one-way permutation. Previous obfuscators for point functions, under varying notions of security, are either probabilistic or in the random oracle model (but work for arbitrary distributions on the point function). On the negative side, we show that - Following Hada and Wee, any family of deterministic functions that can be obfuscated according to our definition must already be ``approximately learnable.'' Thus, many deterministic functions cannot be obfuscated. However, a probabilistic functionality such as a probabilistic secret-key encryption scheme can potentially be obfuscated. In particular, this is possible for a public-key encryption scheme when viewed as a secret-key scheme. - There exists a secure probabilistic secret-key encryption scheme that cannot be obfuscated according to our definition. Thus, we cannot hope for a general-purpose cryptographic obfuscator for encryption schemes.
2005
CRYPTO
2005
PKC
2005
TCC
2005
EPRINT
Generic Constructions of Identity-Based and Certificateless KEMs
We extend the concept of key encapsulation mechanisms to the primitives of ID-based and certificateless encryption. We show that the natural combination of ID-KEMs or CL-KEMs with data encapsulation mechanisms results in encryption schemes which are secure in a strong sense. In addition, we give generic constructions of ID-KEMs and CL-KEMs, as well as specific instantiations, which are provably secure.
2005
EPRINT
An Efficient ID-KEM Based On The Sakai-Kasahara Key Construction
We describe an identity based key encapsulation mechanism (ID-KEM). It is possible to use this ID-KEM to build a secure identity based encryption scheme using the techniques of Bentahar et al. The resulting encryption scheme has a number of performance advantages over existing methods.
2005
EPRINT
Searchable Encryption Revisited: Consistency Properties, Relation to Anonymous IBE, and Extensions
We identify and fill some gaps with regard to consistency (the extent to which false positives are produced) for public-key encryption with keyword search (PEKS). We define computational and statistical relaxations of the existing notion of perfect consistency, show that the scheme of Boneh et al. in Eurocrypt 2004 is computationally consistent, and provide a new scheme that is statistically consistent. We also provide a transform of an anonymous IBE scheme to a secure PEKS scheme that, unlike the previous one, guarantees consistency. Finally, we suggest three extensions of the basic notions considered here, namely anonymous HIBE, public-key encryption with temporary keyword search, and identity-based encryption with keyword search.
2004
EPRINT
Improved Identity-Based Signcryption
Liqun Chen John Malone-Lee
We present an identity-based signcryption scheme that we believe is the most efficient proposed to date. We provide random oracle model~\cite{ROP} proofs of security under the definitions proposed in~\cite{MIBS}
2004
EPRINT
Escrow-Free Encryption Supporting Cryptographic Workflow
Since Boneh and Franklin published their seminal paper on identity based encryption (IBE) using the Weil pairing , there has been a great deal of interest in cryptographic primitives based on elliptic-curve pairings. One particularly interesting application has been to control access to data, via possibly complex policies. In this paper we continue the research in this vein. We present an encryption scheme such that the receiver of an encrypted message can only decrypt if it satisfies a particular policy chosen by the sender at the time of encryption. Unlike standard IBE, our encryption scheme is escrow free in that no key-issuing authority (or colluding set of key-issuing authorities) is able to decrypt ciphertexts itself. In addition we describe a security model for the scenario in question and provide proofs of security for our scheme (in the random oracle model).
2004
EPRINT
Secure Computation of the Mean and Related Statistics
Eike Kiltz Gregor Leander John Malone-Lee
In recent years there has been massive progress in the development of technologies for storing and processing of data. If statistical analysis could be applied to such data when it is distributed between several organisations, there could be huge benefits. Unfortunately, in many cases, for legal or commercial reasons, this is not possible. The idea of using the theory of multi-party computation to analyse efficient algorithms for privacy preserving data-mining was proposed by Pinkas and Lindell. The point is that algorithms developed in this way can be used to overcome the apparent impasse described above: the owners of data can, in effect, pool their data while ensuring that privacy is maintained. Motivated by this, we describe how to securely compute the mean of an attribute value in a database that is shared between two parties. We also demonstrate that existing solutions in the literature that could be used to do this leak information, therefore underlining the importance of applying rigorous theoretical analysis rather than settling for ad hoc techniques.
2003
EPRINT
Universal Padding Schemes for RSA with Optimal Bandwidth of Message Recovery
Wenbo Mao John Malone-Lee
We prove that three OAEP-inspired randomised padding schemes (i.e., OAEP, OAEP+ and SAEP), when used with the RSA function in the trapdoor direction, form provably secure signature schemes with message recovery. Two of our three reductionist proofs are tight and hence provide exact security. Because of the exact security and OAEP's optimally high bandwidth for message recovery, our results form a desirable improvement from a previous universal RSA padding scheme good for both encryption and signature.
2002
CRYPTO
2002
EPRINT
Identity-Based Signcryption
John Malone-Lee
A signcryption scheme is a scheme that provides private and authenticated delivery of messages between two parties. It does this in a more efficient manner than a straightforward composition of an encryption scheme with a signature scheme. An identity-based cryptosystem is one in which the public key may be any string (or may be derived from any string). In this paper we propose an identity-based signcryption scheme. We give a security model for such a scheme and sketch the details of how our scheme may be proved secure in this model.