On Secure Bulletin Boards for E-Voting

Annabell Kuldmaa
Vote collection together with storage of collected votes is the first phase of practically any electronic voting (e-voting) protocol. This functionality is provided by a bulletin board system. Many research papers in e-voting require the existence of a secure bulletin board, but there are only a few concrete systems. In the literature it is common to assume that bulletin board is a centralized trusted party, but in recent works the importance of a distributed fault-tolerant bulletin board has been raised.
In this thesis, we propose a formal model for analysis of security and functionality of a bulletin board system motivated by the security requirements Culnane and Schneider introduced in Computer Security Foundations Symposium 2014. We consider a secure bulletin board as a robust public transaction ledger presented by Garay et al. in Eurocrypt 2015 that additionally provides receipts for successful postings. More precisely, we introduce two properties: (Confirmable) Persistence and Confirmable Liveness.
We study a bulletin board system proposed by Culnane and Schneider in our model, and show that their protocol does not achieve Confirmable Liveness if there exist corrupted item collection peers, but achieves Confirmable Persistence for < N/3 corrupted item collection peers using only our trivial threshold signature scheme, otherwise the bound is < N/4. Motivated by the security analysis of Culnane-Schneider bulletin board system, we propose a fully secure bulletin board system and prove that it tolerates < N/3 corrupted item collection peers for Confirmable Persistence and < N/2 corrupted item collection peers for Confirmable Liveness.
This thesis is based on a submitted paper "A Cryptographic Approach to Bulletin Boards" with co-authors Aggelos Kiayas, Helger Lipmaa, Janno Siim and Thomas Zacharias.
Graduation Thesis language
Graduation Thesis type
Master - Computer Science
Helger Lipmaa
Defence year