## Section: New Results

### Modeling and verifying the Pastry routing protocol

Participants : Tianxiang Lu, Stephan Merz.

As a significant case study for the techniques that we are developing within
VeriDis, we are modeling and verifying the routing protocol of the Pastry
algorithm [25] for maintaining a distributed hash
table in a peer-to-peer network. As part of his PhD work (under the joint
supervision of Stephan Merz and Christoph Weidenbach from MPI-INF
Saarbrücken), Tianxiang Lu has
developed a TLA^{+} model of the Pastry routing protocol, which has uncovered
several issues in the existing presentations of the protocol in the
literature, and in particular a loophole in the join protocol that had been
fixed by the algorithm designers in a technical report that appeared after the
publication of the original protocol.

In 2011, we have worked towards a correctness proof of the routing protocol. We have in particular identified a number of candidate invariants that have been validated by extensive model checking over finite instances and for which we have formally proved that their validity would imply the correctness of the protocol. Our proofs are carried out in TLAPS (section 5.2 ) and represent a sizable case study for the different proof tools of the proof system. Our results have been presented at FORTE 2011 [12] .