Privacy in transit: three protocol upgrades aimed at the metadata layer
Cloudflare today announced work on three privacy-focused protocol initiatives: Encrypted Client Hello (ECH), Oblivious DNS-over-HTTPS (ODoH), and OPAQUE. The common thread is metadata — the information exposed while data moves across the Internet — and all three are designed to shrink the surface that third parties, including network operators and service providers, can observe.
The work follows a roughly year-long effort with contributors from Mozilla, Google, Equinix, Apple, Fastly, and others, coordinated through standards bodies such as the IETF and IRTF. Each initiative targets a different point where sensitive information becomes visible on the wire.
Why metadata still leaks under HTTPS
The shift to widespread HTTPS encryption has removed much of the plaintext content from web traffic, but it has not protected everything. The hostname a user connects to, the DNS queries that resolve it, and the user’s IP address all remain visible to parties along the network path. That distinction between data and metadata matters: content is now encrypted by default thanks to protocols like TLS 1.3, but the metadata that reveals browsing patterns is still exposed.
The Internet Architecture Board has weighed in on this tension. RFC 8890 instructs protocol designers to favor end users over service providers, corporations, or governments when interests conflict, and RFC 6973 provides guidance on how to incorporate privacy considerations into protocol design. RFC 8558 frames the practical problem: on-path parties need some metadata to route traffic, but protocols should minimize what is exposed beyond what is operationally necessary.
When an observer can see both a user’s identity and their activity, profiling becomes possible. A DNS resolver, for instance, necessarily learns which hostnames a user is looking up. Individual websites do not usually see both the user’s IP address and their broader browsing history in the same way, but DNS providers routinely do. The issue is that a resolver does not actually need to know both the queried hostname and the user’s IP address simultaneously.
A history of infrastructure-level security work
These announcements continue a longer pattern of protocol-level work at Cloudflare. In 2014, the company launched Universal SSL, which helped push the share of encrypted connections to websites from roughly 30 percent to around 80 percent industry-wide. Cloudflare engineers also contributed early drafts and testing for TLS 1.3 and were early adopters of QUIC. On the operational side, the company has built an RPKI toolkit for securing BGP routing, published route-leak measurement research, and operates “Is BGP Safe Yet” as a public check on routing security. Its time service supports NTS and Roughtime, and its 1.1.1.1 resolver shipped with DNS-over-HTTPS and DNS-over-TLS support at launch.
The underlying principle, as Cloudflare frames it, is that Internet infrastructure should default to limiting what on-path systems can observe. Users do not have agreements with every transit provider or middlebox that touches their traffic, and consent mechanisms belong at the application layer, not in the protocols that carry data underneath.
Combining cryptography and proxies
Two techniques dominate the design of privacy-preserving protocols today. Cryptography restricts data readability to key holders, turning data security problems into key management problems. Secure proxies enforce policy by isolating parties and controlling which data crosses a boundary. Used separately, each has limits; used together, they can hide both content and attribution.
Onion routing — the technique underlying Tor — is the canonical example. A similar pattern appears in the protocols announced today: data is encrypted for one party, metadata is encrypted for another, and a proxy mediates the exchange so that neither party sees the full picture.
What the three protocols actually change
ECH addresses one of the last plaintext fields remaining in TLS. The Client Hello — the first message a client sends during a handshake — still carries the hostname in cleartext when connecting via HTTPS, even under TLS 1.3. ECH encrypts that field using a key the client fetches ahead of time, so the destination hostname is no longer visible to observers on the path.
ODoH targets DNS resolution privacy. Standard DNS-over-HTTPS hides queries from an ISP but still reveals the user’s IP address to the resolver, creating a single point that can correlate identity with lookup history. ODoH inserts a proxy between the client and the resolver. The client encrypts its query so the proxy cannot read it and encrypts its own identity so the resolver cannot associate the query with a source IP. The resolver learns the hostname and the proxy learns the source, but neither learns both.
OPAQUE changes password authentication. In a standard setup, the server holds a verifier derived from the password; a database breach exposes that verifier to offline guessing. OPAQUE uses an Oblivious Pseudo-Random Function so the server never sees the password itself — it can only determine whether the client knows the correct password. Even a fully compromised server cannot recover the password or mount an offline dictionary attack.
Each protocol exposes less data to fewer parties. ECH removes hostnames from the network path, ODoH prevents a single DNS operator from linking identity to queries, and OPAQUE removes the password from the server’s field of view entirely.
Working in the open
These protocols are not unilateral designs. Each has gone through the consensus process of the IETF or IRTF, involving browser vendors, cryptographers, DNS operators, and academic researchers. Cloudflare notes that it is also engaging with governments and civil society on the legal and policy implications of wider adoption, since changes to core Internet protocols carry consequences beyond the technical community.
All three projects were built with contributions from Cloudflare Research, including work by interns. The company is hiring for related roles.
