Linear-time Self-stabilizing Byzantine Clock Synchronization

Clock synchronization is a very fundamental task in distributed system. It thus makes sense to require an underlying clock synchronization mechanism to be highly fault-tolerant. A self-stabilizing algorithm seeks to attain synchronization once lost; a Byzantine algorithm assumes synchronization is never lost and focuses on containing the influence of the permanent presence of faulty nodes. There are efficient self-stabilizing solutions for clock synchronization as well as efficient solutions that are resilient to Byzantine faults. In contrast, to the best of our knowledge there is no practical solution that is self-stabilizing while tolerating the permanent presence of Byzantine nodes. We present the first linear-time self-stabilizing Byzantine clock synchronization algorithm. Our deterministic clock synchronization algorithm is based on the observation that all clock synchronization algorithms require events for exchanging clock values and re-synchronizing the clocks to within safe bounds. These events usually need to happen synchronously at the different nodes. In classic Byzantine algorithms this is fulfilled or aided by having the clocks initially close to each other and thus the actual clock values can be used for synchronizing the events. This implies that clock values cannot differ arbitrarily, which necessarily renders these solutions to be non-stabilizing. Our scheme suggests using an underlying distributed pulse synchronization module that is uncorrelated to the clock values.