ffdhe2048
ffdhe2048 is a named 2048-bit finite-field Diffie-Hellman group from RFC 7919. Libraries offer it, Chrome does not.
What it is
ffdhe2048 (group 256) is one of the named finite-field Diffie-Hellman groups defined in RFC 7919. Before that RFC, a TLS 1.2 server running a DHE cipher suite chose its own Diffie-Hellman prime, and clients had no way to ask for a safe size. RFC 7919 fixed this by publishing well-studied groups and letting the client list them in supported_groups.
In TLS 1.3, finite-field groups can be used for the key exchange through key_share like the elliptic curves. ffdhe2048 offers roughly 103 bits of security according to RFC 7919, less than x25519, while being much slower and producing larger key shares.
For these reasons, clients that offer it put it after all their elliptic curves.
RFC 8446 leaves the choice to the server; listing the elliptic curves first signals that the client prefers them.
Who sends it
Measured on 2026-10-25 against our own test server: sent by 7 of 12 clients. Position counts from 1 and ignores GREASE values.
Why it matters for fingerprinting
Python requests, httpx, Node.js fetch, Guzzle, Debian curl and the Firefox profile of curl-impersonate offer it; Chrome, curl_cffi, the Chrome profile of curl-impersonate, macOS curl and Go net/http do not. It is usually at position 5 to 7, after the elliptic curves.
Check whether your client sends it
Open the test from your browser, or call it from your script, and look for ffdhe2048 in the TLS details.
Run the TLS fingerprint test