Transferring files between servers on a private network?

[Brian Candler]

On 09/12/2020 18:45, Steve Dondley wrote:
> Ok, thanks for the insight.
>
> Yeah, I was trying to avoid agent forwarding because of the advice 
> I've seen to avoid it, if possible.

As far as I know, you'd mainly want to avoid it if you don't trust the 
left-hand machine (i.e. the source, the one you called "B").  A 
malicious administrator on that host could connect to your agent socket 
and authenticate, as you, to any other machine that trusts your key.

But to be honest, if a machine is malicious, I wouldn't want to ssh into 
it in the first place.  It could do plenty of other nasty things, such 
as logging my keystrokes.

>
> Only other method I can think of is to have a third machine, machine 
> C, that is only available on the private network and contains the 
> private key for all the other machines. So I'd log into machine C via 
> some bastion/jump server. Machine C would hold the private the 
> key used by machine B and machine A and I could use it to transfer 
> files between machines A and B.

Copying your private key onto other machines is, in general, way less 
secure than using agent forwarding.

You could ssh to C (that you trust), with agent forwarding enabled, and 
use it to third-party copy between B and A (*without* enabling agent 
forwarding from C to B or C to A)