Privacy Pass Protocol

1/28/2020

This post details Cloudflare's commitment to data privacy and outlines several privacy-enhancing technologies they have released or support, including Universal SSL, Privacy Pass, ESNI, 1.1.1.1 Public DNS Resolver, DNS over HTTPS (DoH), and the 1.1.1.1 Mobile Application with WARP. It also describes how Cloudflare infuses privacy principles into its operations through employee education, privacy-by-design in product development, internal compliance with regulations, and security as a means to enhance privacy.

10/28/2019

This post details the advancements in Cloudflare's support for the Privacy Pass protocol, introducing version 2.0 of the browser extension and a new server backend built on Cloudflare Workers. Key updates include easier configuration, integration with hCaptcha, compliance with hash-to-curve standards, and independent key rotation. The server backend utilizes the V8 engine for cryptographic operations and offers a public redemption API. Cryptographic improvements in the extension include zero-knowledge proof validation and optimized ECC using NIST P-256 with SSWU hashing. The post also highlights ongoing standardization efforts for OPRFs and the Privacy Pass protocol itself.

9/24/2018

This post introduces Encrypted SNI (ESNI) as an extension to TLS 1.3, building upon existing privacy features like Privacy Pass and encrypted DNS. It details how ESNI works by encrypting the SNI extension using a key derived from a public key published in DNS, preventing on-path observers from identifying visited websites. The post explains the cryptographic mechanisms involved (Diffie-Hellman) and the importance of TLS 1.3's encrypted certificate message. It also addresses the potential vulnerability of unencrypted DNS queries and the role of DNSSEC and DoT/DoH in mitigating this. Finally, it announces the free availability of ESNI for all Cloudflare zones and its upcoming support in Firefox Nightly.

9/24/2018

This post announces the launch of Encrypted SNI (ESNI) across Cloudflare's network, a protocol designed to encrypt the Server Name Indication (SNI) extension in TLS handshakes. This addresses a privacy leak where the SNI, which identifies the hostname being accessed, was previously sent in plaintext. Cloudflare worked with industry partners like Mozilla, Apple, and Fastly on the ESNI protocol, which is being standardized as an IETF Draft RFC. Firefox Nightly is the first browser to support ESNI.

9/24/2018

This post announces the launch of Encrypted SNI (ESNI) across Cloudflare's network, marking a significant step in enhancing internet privacy. ESNI encrypts the Server Name Indication (SNI) field in TLS handshakes, preventing network observers (like ISPs) from seeing which website a user is visiting, even over HTTPS. This addresses a critical privacy leak in the existing encrypted web. Cloudflare collaborated with Apple, Fastly, and Mozilla on ESNI, and it is being standardized as an IETF draft RFC. Mozilla's Firefox is expected to be the first browser to support ESNI. The post also references the earlier launch of 1.1.1.1 as a privacy-enhancing DNS resolver and highlights the historical context of Cloudflare's commitment to making the web more private and secure, such as the introduction of Universal SSL.

9/20/2018

Introduced Cloudflare Onion Services, which leverage HTTP Alternative Services to allow Tor Browser users to connect directly to Cloudflare's .onion addresses. This bypasses Tor exit nodes, improves security and performance, and enables more fine-grained rate-limiting by using circuit numbers to distinguish individual Tor connections. The implementation involves using a custom TLS 1.3 stack and relaying Client Hello packets to a local server that presents a certificate for the original hostname.

11/9/2017

This post details the mathematical underpinnings of the Privacy Pass protocol, moving from an initial RSA-based blind signing approach to a more efficient elliptic curve cryptography (ECC) based Oblivious Pseudorandom Function (OPRF) construction. It explains the blind signing phase and the redemption phase, highlighting the use of ECC for smaller key sizes and faster operations. The protocol's security relies on the hardness of the discrete logarithm problem and collision-resistant hash functions, ensuring user anonymity and preventing token abuse.

11/9/2017

This post announces Cloudflare's support for the Privacy Pass protocol, a privacy-preserving technology that uses zero-knowledge proofs to allow users to prove they are human without revealing their identity. It explains the problem of distinguishing bots from legitimate users, especially for anonymous users, and how Privacy Pass reduces the number of challenge pages presented by Cloudflare. The post also details the technical implementation using a voting analogy for zero-knowledge proofs and encourages open-source contributions.