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Title: Encryption in the presence of key-dependent messages and related-key attacks
Author: Davies, Gareth Thomas
ISNI:       0000 0004 5917 4793
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2015
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This thesis investigates enhanced adversarial models for encryption, for scenarios where established notions of security are not sufficient to accurately model the capabilities of real-world adversaries. In particular we focus on achieving encryption schemes that are secure even when the adversary has more power than granted by standard notions such as indistinguishability under chosen-plaintext attack (IND-CPA). These extended models allow researchers, implementors and end-users to confidently pinpoint areas of strength and weakness in cryptographic hardware and software. Our first contribution considers key-dependent message (KDM) security, meaning security even when an adversary has access to encryptions of the decryption key. Our focus is the hybrid encryption framework, a method for public key encryption that is widely deployed. We give sufficient conditions for achieving KOM security for this paradigm in the random oracle model using novel proof techniques, and cast known impossibility results in KOM security in the context of hybrid encryption. Next we investigate modelling an adversary that is yet more powerful: related-key-attackand- key-dependent message (RKA-KDM) security considers when an adversary has to access encryptions, performed under related keys, of key-dependent messages. Our main result is a composition theorem showing how to generically achieve RKA-KDM security. To indicate the efficacy of our approach, we present a number of symmetric key instantiations that use known KDM-secure public key encryption schemes as a starting point.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available