International Association for Cryptologic Research

Ph.D. Database

The aim of the IACR Ph.D. database is twofold. On the first hand, we want to offer an overview of Ph.D. already completed in the domain of cryptology. Where possible, this should also include a subject classification, an abstract, and access to the full text. On the second hand, it deals with Ph.D. subjects currently under investigation. This way, we provide a timely map of contemporary research in cryptology. All entries or changes need to be approved by an editor. You can contact them via phds (at)


Dalia Khader (#426)
Name Dalia Khader
Institution University of Bath
Topic of his/her doctorate. Attribute based authentication schemes
Category public-key cryptography
Keywords identity based cryptography, digital signatures, Attribute Based Cryptography
Ph.D. Supervisor(s) Russell Bradford
Year of completion 2009

This thesis’ major contribution is to propose an attribute based authentication scheme (AAS). An AAS scheme is a new cryptosystem that extends the field of public key cryptography and more precisely digital signatures. An AAS scheme allows a verifier to decide on the set of attributes (s)he would like the signer to possess. The verifier sends the request to a group of possible signers as a monotone boolean expression. Any member with sufficient attributes can sign. The scheme maintains certain properties as follows:

[1] No previous knowledge assumption: The signer and verifier may or may not have met before; therefore we can not rely on any kind of previous knowledge.

[2] Unforgeable : It is hard to forge signatures and/or the proof of possession of attributes.

[3] Anonymous Identities: Given the signature it is hard to identify the signer.

[4] Unlinkable: Given two signatures it is hard to know whether the signer is the same or not.

[5] Traceable: Each group of potential signers have a group manager and he is the only one capable of revoking anonymity and discovering the signer’s identity. This property is meant to ensure signers do not misuse anonymity.

[6] Anonymous Attributes: The attribute disclosure should be to the minimum.

[7] Coalition Resistant: If a verifier requires more than one attribute from the signers, the signers should not be able to get together their individual attributes and sign as one entity.

[8] Separability: The tasks of different authorities should be separable and each entity should be capable of performing its task independently from others.

Different attribute oriented authentication schemes exist in literature, however each of them is designed to serve a certain application. However the properties we listed above never co-existed in one scheme. This thesis goes through various designs for such a system, proofs security for them all and finally provides a general construction from any group signature to an AAS.

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