backporting sntrup761x25519-sha512 key exchange to OpenSSH 8.9-9.8

[Damien Miller]

On Mon, 11 Aug 2025, Theo de Raadt wrote:

> Damien Miller <djm at mindrot.org> wrote:
> 
> > Hi,
> > 
> > I have just made a series of commits to the stable branches of portable
> > OpenSSH versions 8.9 through 9.8 to enable the "sntrup761x25519-sha512"
> > key agreement algorithm.
> > 
> > This algorithm is the IANA-allocated name for the existing post-quantum
> > algorithm "sntrup761x25519-sha512 at openssh.com". Apart from the name,
> > "sntrup761x25519-sha512" is completely identical and it was only a
> > trivial change to enable the new standard name as an additional
> > alias.
> 
> It's been pointed out there are some lazy people :-)
> 
> So this is the tiny change to pickup:
> 
> https://github.com/openssh/openssh-portable/commit/ffdbae4c0201d42bfa1f5c5e9c21454d10795491
> 
> That probably patches into most of the versions above 8.9 or you can find
> the exact patch you need.

There are some very minor and obvious differences that up to openssh-9.7
after which the patch is a bit different.

-d