HTTPS is a cornerstone of privacy in the modern Web. The public key infrastructure underlying HTTPS, however, is a frequent target of attacks. In several cases, forged certificates have been issued by compromised Certificate Authorities (CA) and used to spy on users at large scale. While the concept of Certificate Transparency (CT) provides a means for detecting such forgeries, it builds on a distributed system of CT logs whose correctness is still insufficiently protected. By compromising a certificate authority and the corresponding log, a covert adversary can still issue rogue certificates unnoticed. We introduce LogPicker, a novel protocol for strengthening the public key infrastructure of HTTPS. LogPicker enables a pool of CT logs to collaborate, where a randomly selected log includes the certificate while the rest witness and testify the certificate issuance process. As a result, CT logs become capable of auditing the log in charge independently without the need for a trusted third party. This auditing forces an attacker to control each participating witness, which significantly raises the bar for issuing rogue certificates. LogPicker is efficient and designed to be deployed incrementally, allowing a smooth transition towards a more secure Web.

The recent years have brought an in ux of privacy conscious applications, that enable strong security guarantees for end-users via end-to-end or client-side encryption. Unfortunately, this application paradigm is not easily transferable to web-based cloud applications. The reason for this lies within adversary's enhanced control over client-side computing through application provided JavaScript. In this paper, we propose C M-a set of native client-side components that allow the development of web applications which provide a robust isolation layer between the client-side encrypted user data and the potentially untrusted JavaScript, while maintaining full interoperability with current client-side development practices. In addition, to enable a realistic transition phase, we show how C M can be realized for currently existing web browsers via a standard browser extension. CCS CONCEPTS • Security and privacy → Web application security; Browser security.