  The level of trust accorded to certification authorities has been decreasing
over the last few years as several cases of misbehavior and compromise have
been observed. Log-based approaches, such as Certificate Transparency, ensure
that fraudulent TLS certificates become publicly visible. However, a key
element that log-based approaches still lack is a way for clients to verify
that the log behaves in a consistent and honest manner. This task is
challenging due to privacy, efficiency, and deployability reasons. In this
paper, we propose the first (to the best of our knowledge) gossip protocols
that enable the detection of log inconsistencies. We analyze these protocols
and present the results of a simulation based on real Internet traffic traces.
We also give a deployment plan, discuss technical issues, and present an
implementation.
