Helger Lipmaa's publications

Accountable Certificate Management using Undeniable Attestations

Ahto Buldas, Peeter Laud and Helger Lipmaa. Accountable Certificate Management using Undeniable Attestations. In Sushil Jajodia and Pierangela Samarati, editors, 7th ACM Conference on Computer and Communications Security, pages 9--18, Athens, Greece, November 1--4, 2000. ACM Press. ISBN ACM ISBN 1-58113-203-4.

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This paper initiates a study of accountable certificate management methods, necessary to support long-term authenticity of digital documents. Our main contribution is a model for accountable certificate management, where clients receive attestations confirming inclusion/removal of their certificates from the database of valid certificates. We explain why accountability depends on the inability of the third parties to create contradictory attestations. After that we define an undeniable attester as a primitive that provides efficient attestation creation, publishing and verification, so that it is intractable to create contradictory attestations. We introduce authenticated search trees and build an efficient undeniable attester upon them. The proposed system is the first accountable long-term certificate management system. Moreover, authenticated search trees can be used in many security-critical applications instead of the (sorted) hash trees to reduce trust in the authorities, without decrease in efficiency. Therefore, the undeniable attester promises looks like a very useful cryptographic primitive with a wide range of applications.

Keywords: Accountable certificate management, authenticated search trees, attesters, long-term authenticity, non-repudiation, public-key infrastructure, search trees, time-stamping.


Superseded by: The final journal version of this paper has been published. It supersedes this publication. Final version here. Please read the journal version!

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