Hans Heum defends his PhD thesis
Published:
On 8 December, Hans Heum will defend his PhD thesis Hans Heum “Cryptology in the Crowd” The defence takes place in Store auditorium at UiB's Høyteknologisenteret at 13:00.
Main research findings
Accidents happen: Perhaps you lost the key to your house or had the PIN code for your burglar alarm written on a poorly placed post-it note. And maybe they ended up in the hands of the wrong person, who can now cause all sorts of mischief in your life: Security systems offer no guarantees when keys are stolen and PIN codes are leaked. Nevertheless, your neighbour, whose key-and-PIN-code routines are rather watertight, should feel secure in the knowledge that even if you can't secure your home against break-ins, theirs remains safe.
The same applies to cryptography, which also relies on keeping key material secret to guarantee security: Intuitively, one expects that knowledge of one system's secret key should not be helpful in breaking into other unrelated systems. However, it has proven surprisingly difficult to formalise this intuition, and several competing security models of varying strength have emerged. It is therefore natural to ask: What is the right formalisation when modelling realistic scenarios with many users and potential leaks? Or: How does one build cryptography in a crowd?
The dissertation explores the various ways the scenarios above can be formalised in mathematical models and demonstrates that some formalisations are stronger than, and therefore preferred over, others. These formalisations are then organised, and over 30 different security models are compared. Furthermore, the dissertation shows how to provide formalisations that capture scenarios like mass surveillance by asking how easy it would be for an unwanted actor to break into more than one cryptographic system at a time. A public-key cryptosystem is presented, and it is proven that the construction achieves optimal security in such a mass surveillance scenario.
Adjudication committee
- Research Staff Member Julia Hesse, IBM Zurich
- Associate Professor Jiaxin Pan, University of Kassel
Chair of the committee
- Chief Research Scientist Håvard Raddum, Simula UiB
Leader of the public defence
- Professor Magne Haveraaen, Department of Informatics, University of Bergen
Supervisors
- Main supervisor: Chief Research Scientist Martijn Stam, Department of Cryptography, Simula UiB
- Co-supervisor: Research Director Øyvind Ytrehus, Simula UiB
More information about the event is found at uib.no
