Charmaine Ndolo

Charmaine Ndolo, Florian Tschorsch

Bitcoin recently introduced a new protocol for the encryption of peer-to-peer (P2P) communication. The protocol, known as V2 P2P transport, represents a big step towards securing the overlay network against various previously-known attack vectors. Based on an analysis of V2 P2P transport, this work examines the current viability of said attacks and concludes that while they are now remediated, alternative attacks and paths to similar objectives exist. The identified shortcomings are conceptual (and not implementation bugs) and even applicable to other P2P networks. We show how a network-level attacker can identify application messages using the length of TCP payloads, can eclipse a target node by taking advantage of how encrypted communication channels work and can downgrade all of a node's connections to the unencrypted protocol by using the mechanisms designed for compatibility. We validate our contributions using a combination of network measurements, emulations and simulations. Finally, we propose a series of short-term and long-term countermeasures towards securing Bitcoin's P2P network. To the best of our knowledge, we are the first to study Bitcoin's security under V2 P2P transport.

Charmaine Ndolo, Sebastian Henningsen, Martin Florian

We continuously crawl the young MobileCoin network, uncovering the quorum configurations of core nodes and the quorum system resulting from these configurations. This report discusses our crawl methodology, encountered challenges, and our current empirical results. We find that the MobileCoin quorum system currently comprises of 7 organisations controlling a total of 10 validator nodes. Current quorum set configurations prioritise safety over liveness. At the time of writing, one of the involved organisations is technically able to block the approval of new blocks, as is the case for one of the (two) ISPs employed by crawled nodes.

Martin Florian, Sebastian Henningsen, Charmaine Ndolo et al.

Federated Byzantine Agreement Systems (FBASs) are a fascinating new paradigm in the context of consensus protocols. Originally proposed for powering the Stellar payment network, FBASs can instantiate Byzantine quorum systems without requiring out-of-band agreement on a common set of validators; every node is free to decide for itself with whom it requires agreement. Sybil-resistant and yet energy-efficient consensus protocols can therefore be built upon FBASs, and the "decentrality" possible with the FBAS paradigm might be sufficient to reduce the use of environmentally unsustainable proof-of-work protocols. In this paper, we first demonstrate how the robustness of individual FBASs can be determined, by precisely determining their safety and liveness buffers and therefore enabling a comparison with threshold-based quorum systems. Using simulations and example node configuration strategies, we then empirically investigate the hypothesis that while FBASs can be bootstrapped in a bottom-up fashion from individual preferences, strategic considerations should additionally be applied by node operators in order to arrive at FBASs that are robust and amenable to monitoring. Finally, we investigate the reported "open-membership" property of FBASs. We observe that an often small group of nodes is exclusively relevant for determining liveness buffers and prove that membership in this top tier is conditional on the approval by current top tier nodes if maintaining safety is a core requirement.