Proton Mail’s open-source encryption library, OpenPGPjs, has passed an independent security audit

At Proton Mail, our goal is to make encryption as widespread and accessible as possible. We believe a key step toward that is having well-maintained, robust, and secure open source encryption libraries. This is the goal of our efforts on the OpenPGPjs encryption library, which is today used by hundreds of applications (including Proton Mail) serving millions around the world. As the maintainer of OpenPGPjs, we are responsible for making sure the library is up to date and secure, as well as offering basic support to developers who wish to use it.

In March 2018, we released Version 3.0 of OpenPGPjs. With this major update, OpenPGPjs is even more powerful, secure, and efficient. As part of this update, the OpenPGPjs developer community commissioned an independent security audit from the well-respected security firm Cure53. Independent security audits are an important way to ensure there are no vulnerabilities that could be exploited by attackers.

Summer 2018 Security Audit Coverage

The version 3.0 release brought many new features and improvements, such as support for elliptic curve cryptography (ECC), which uses smaller signing and encryption keys compared with RSA cryptography (what Proton Mail uses now), making it a faster and more efficient alternative.

The new version also adds compression, which reduces the size of data before encryption to save space (and time) during encryption and transmission. OpenPGPjs now also offers support for AEAD (Authenticated Encryption with Associated Data). This protocol provides confidentiality, integrity, and authenticity guarantees on encrypted data, so that when you decrypt data, you can be sure this was the exact same data encrypted by your sender, and you can be sure that it was indeed encrypted by that sender. For those who are interested, you can find the full technical details of OpenPGPjs Version 3.0 here.

The Cure53 team focused on a couple of these new features while also taking a closer look at some key aspects of OpenPGPjs’ crypto implementations. In particular, the audit focused on the following:

  • AEAD encrypted packets
  • EAX, GCM, OCB
  • CMAC
  • All cryptographic primitive implementations: AES, AES-EAX, AES-GCM, AES-CBC, ED25519, C25519, ECDSA, HMAC, P256, P384, P521, SECP256K1
  • Prime number handling
  • Date support in signatures
  • Cryptographic API exposure via different providers

OpenPGPjs Audit Results

We are pleased to receive a highly positive result from the audit. No major issues were discovered. In their summary, Cure53 provided the following feedback:

“Tested cryptographic implementations were top notch and excellent quality given the platform. The only limitations come from the platform itself (JavaScript/web), which do not allow for side channel resistance or reliable constant time operations. Overall however this is an exceptional library for JavaScript cryptography.”

As OpenPGPjs forms the foundation of Proton Mail’s encryption, this result provides extra certainty that Proton Mail’s cryptography is properly protecting users as intended. Working with the open source community is an important part of what we do at Proton Mail, and we will continue to build out the OpenPGPjs library. We are grateful to the Proton Mail community for supporting us in these efforts.

Best Regards,
The Proton Mail Team

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