Re: ssh on FreeBSD 14.3 won't talk to older hosts

Frank Leonhardt:

> Add the following:
> 
> HostKeyAlgorithms=+ssh-dss
> PubkeyAcceptedKeyTypes +ssh-rsa
> Protocol 2,1
> 
> I have all three but they may not all be needed in all circumstances, and
> having protocol 1 isn't something you want to enable unless you're aware of
> the risks.

That's cute if "Protocol 2,1" is still accepted for compatibility,
but there is no risk.  The actual protocol 1 code has been summarily
deleted from OpenSSH as of release 7.6 (Oct 2017).

> This is IN SPITE of OpenSSH ssh-keygen still generating RSA by default, so

Actually, that has been Ed25519 since OpenSSH 9.5 (Oct 2023)... but the
FreeBSD -stable branches haven't picked up that change.

> the default key type it creates it won't use without this hack. Unless I'm
> missing something.

There is a difference between a _key type_ and a _public key algorithm_.
Admittely, those are the same for all other key types except for RSA,
where there are three algorithms that can all use the same RSA keys:
* ssh-rsa
* rsa-sha2-256
* rsa-sha2-512

The difference is that those use the SHA-1, SHA-256, and SHA-512
hashes, respectively.  SHA-1 is obsolete and no longer considered
secure, so the "ssh-rsa" _algorithm_ has been disabled by default.
You can still use the same "ssh-rsa" _keys_ with rsa-sha2-256 or
rsa-sha2-512.

-- 
Christian "naddy" Weisgerber                          naddy@mips.inka.de