Security Through Transparency

Posted by Ryan Hurst and Gary Belvin, Security and Privacy Engineering
Encryption is a foundational technology for the web. We’ve spent a lot of time working through the intricacies of making encrypted apps easy to use and in the process, realized that a generic, secure way to discover a recipient's public keys for addressing messages correctly is important. Not only would such a thing be beneficial across many applications, but nothing like this exists as a generic technology.

A solution would need to reliably scale to internet size while providing a way to establish secure communications through untrusted servers. It became clear that if we combined insights from Certificate Transparency and CONIKS we could build a system with the properties we wanted and more.

The result is Key Transparency, which we’re making available as an open-source prototype today.

Why Key Transparency is useful

Existing methods of protecting users against server compromise require users to manually verify recipients’ accounts in-person. This simply hasn’t worked. The PGP web-of-trust for encrypted email is just one example: over 20 years after its invention, most people still can't or won’t use it, including its original author. Messaging apps, file sharing, and software updates also suffer from the same challenge.

One of our goals with Key Transparency was to simplify this process and create infrastructure that allows making it usable by non-experts. The relationship between online personas and public keys should be automatically verifiable and publicly auditable. Users should be able to see all the keys that have been attached to an account, while making any attempt to tamper with the record publicly visible. This also ensures that senders will always use the same keys that account owners are verifying.

Key Transparency is a general-use, transparent directory that makes it easy for developers to create systems of all kinds with independently auditable account data. It can be used in a variety of scenarios where data needs to be encrypted or authenticated. It can be used to make security features that are easy for people to understand while supporting important user needs like account recovery.

Looking ahead
It’s still very early days for Key Transparency. With this first open source release, we’re continuing a conversation with the crypto community and other industry leaders, soliciting feedback, and working toward creating a standard that can help advance security for everyone.

We’d also like to thank our many collaborators during Key Transparency’s multi-year development, including the CONIKS team, Open Whisper Systems, as well as the security engineering teams at Yahoo! and internally at Google.

Our goal is to evolve Key Transparency into an open-source, generic, scalable, and interoperable directory of public keys with an ecosystem of mutually auditing directories. We welcome your apps, input, and contributions to this new technology at KeyTransparency.org.