Comment 29 for bug 907675

It's been a while and there's been some progress, so here's an update:

 * cryptography 2.6 has been released with X25519 and Ed25519 support.
 * Ubuntu 18.04 has been updated to OpenSSL 1.1.1.
 * I've pushed PRs to Twisted (https://twistedmatrix.com/trac/ticket/9681 and https://twistedmatrix.com/trac/ticket/9682) to begin the process of being able to write OpenSSH's newish (v1) private key format, which is the only format OpenSSH supports for Ed25519 keys; while this isn't strictly needed in order to support Ed25519 as a server, doing this first makes the patch series much more manageable.

Still to do:

 * Finish support for writing OpenSSH v1 private keys (https://twistedmatrix.com/trac/ticket/9683).
 * Add curve25519-sha256 key exchange support to Twisted. (I have a tested branch for this, waiting on the items above.)
 * Add Ed25519 key support to Twisted. (I have a tested branch for this, waiting on the items above.)
 * Either:
  * Upgrade Ubuntu 18.04 to OpenSSL 1.1.1b or newer (1.1.1 had a signature verification bug: https://github.com/openssl/openssl/issues/7693), and upgrade the relevant Launchpad production systems from Ubuntu 16.04 to 18.04, which may be tractable; or:
  * Add a fallback mechanism to Twisted allowing it to support Ed25519 keys using PyNaCl or similar if a sufficient version of OpenSSL isn't installed.
 * Wait for a Twisted release with all this in it, and upgrade Launchpad to it. We're on a relatively recent version at the moment, so this part should be easy enough.