International Association
for Cryptologic Research

The need for third-party auditors in privacy-preserving Key Transparency (KT) systems presents a deployment challenge. In this short note, we take a simple privacy-preserving KT system that provides strong security guarantees in the presence of an honest auditor (OPTIKS) and show how to add a auditor-free mode to it. The auditor-free mode offers slightly weaker security. We formalize this security property and prove that our proposed protocol satisfies our security definition.