Scalable Decentralized Privacy- Preserving Location Proximity Alexander. M. Bergersen Department of Computer Science CHALMERS UNIVERSITY OF TECHNOLOGY UNIVERSITY OF GOTHENBURG Gothenburg, Sweden 2017 Scalable Decentralized Privacy-Preserving Location Proximity Alexander M. Bergersen Department of Computer Science Chalmers University of Technology University of Gothenburg Gothenburg, Sweden 2017 1 Scalable Decentralized Privacy-Preserving Location Proximity. ALEXANDER M. BERGERSEN © ALEXANDER M. BERGERSEN, 2017 Department of Computer Science Chalmers University of Technology University of Gothenburg SE-412 96 Gothenburg Sweden Telephone + 46 (0)31-772 1000 Department of Computer Science Gothenburg, Sweden 2017 2 Abstract This report is the report of a Master Thesis carried out at Chalmers University of Technology by me, Alexander Bergersen. The aim of the Master Thesis was to introduce authentication into decentralized privacy-preserving location proximity without adversely hampering the scalability of such protocols further. This was done by creating two solutions that slightly modified the behavior of a location proximity protocol called “InnerCircle”. The first solution, called the Gossiping solution, tries to introduce authentication by having the base network be an unstructured distributed network where each client substitutes as an authentication authority for each of the clients connected to it, viewed as its neighbors. This solution assumes a majority honest network where each vote of authenticity from each neighbor carries equal weight. The second solution develops the first one by going in a different direction and uses an Identity Based Encryption system with distributed key generation as the basis. Instead of proving authentication it hides information from those not authorized to see it. However, even though the second solution is based on the first one, they are different enough that instead of the testing each solution and showing the progress, the solutions are compared as to which one is better and most fulfill the aim of not adversely affecting the performance of the underlying protocol, InnerCircle, the best. The test results are presented to the reader for each of three cases, baseline, first solution, second solution, in tables and the data is analyzed. This analysis showed that the Gossiping solution without the Identity Based Encryption will eventually always outperform the second solution, even if the Identity Based solution was developed with the goal of performing better than the Gossiping solution. Keywords: Location Proximity, InnerCircle, Decentralized Cryptography, Distributed Systems 3 Table of Contents Abstract ..............................................................................................................................................0 1.Introduction .....................................................................................................................................6 1.1 Structure ...................................................................................................................................6 2. Theory ............................................................................................................................................8 2.1 Distributed Systems ..................................................................................................................9 2.1.1 Content Addressable Network(CAN) ................................................................................. 11 2.2 Cryptography .......................................................................................................................... 13 2.2.1 Public-key Cryptography ................................................................................................... 13 2.2.2 Location Proximity ............................................................................................................ 16 2.2.3 Secure Multiparty Computation ........................................................................................ 16 2.2.4 InnerCircle ........................................................................................................................ 17 2.3 Elliptic Curves .......................................................................................................................... 19 2.4 Elliptic Curve Cryptography(ECC) ............................................................................................. 22 2.4.1 Elliptic Curve ElGamal ....................................................................................................... 23 2.5 Identity based encryption(IBE) ................................................................................................ 24 2.5.1 Boneh and Franklin IBE ..................................................................................................... 24 2.5.2 Distributed Identity based encryption ............................................................................... 26 3. Problems and Approach ................................................................................................................ 28 3.1 Challenges ............................................................................................................................... 29 3.1.1 Confidentiality Challenge .................................................................................................. 29 3.1.2 Scaling Challenge .............................................................................................................. 30 3.1.3 The Research Question ..................................................................................................... 31 3.2 Approach ................................................................................................................................ 31 3.2.1 Distributed Systems .......................................................................................................... 31 3.2.2 Cryptography .................................................................................................................... 32 3.2.3 Research method ............................................................................................................. 32 4. Solutions ....................................................................................................................................... 33 4.1 Gossiping ................................................................................................................................ 34 4.1.1 The Idea ........................................................................................................................... 34 4.1.2 How it works .................................................................................................................... 34 4.1.3 What problems does it solve? ........................................................................................... 38 4.1.4 The changes to InnerCircle for the solution ....................................................................... 39 4.1.5 Suggested Implementation ............................................................................................... 39 4.1.6 Security Considerations .................................................................................................... 42 4.2 Cryptography .......................................................................................................................... 45 4 4.2.1 The Idea ........................................................................................................................... 45 4.2.2 How it works .................................................................................................................... 46 4.2.3 What problems does it solve? ........................................................................................... 48 4.2.4 The changes to InnerCircle for the solution ....................................................................... 48 4.2.5 Possible Implementation .................................................................................................. 48 4.2.6 Security Considerations .................................................................................................... 48 5. Testing and Conclusion ................................................................................................................. 51 5.1 Testing .................................................................................................................................... 52 5.1.1 Testing Method ................................................................................................................ 52 5.1.2 Results.............................................................................................................................. 52 5.2 Conclusion .............................................................................................................................. 60 6. Future ........................................................................................................................................... 61 6.1 Future Work ............................................................................................................................ 62 7. Ethical and Social considerations ................................................................................................... 63 7.1 Possible social impact of location proximity ............................................................................