How to print the SSH host key as a client

[Jente Hidskes]

Hi Ján,

Thanks for your reply! I quickly tested with libssh2_session_startup
but it makes no difference unfortunately. It's good to know what I
need is possible with libssh2, though!

I did find that if I retrieve the length of the key, I get 279 (and
the key type is PLAIN). Yet printing it still returns the empty
string.
To show what I mean, here's the output of my code:

$ ./sftp 10.241.167.53 22 user pass
Fingerprint: 28 75 36 2E B2 8B E8 8D 87 63 28 9F 42 0E D1 6F 2D 8B 38 EE
Host key: ""
Host key type: 1
Host key length: 279
all done

I uploaded my example code here[1], in case it helps. I am using libssh2 1.10.0.

Thanks,

Jente

[1] https://gist.github.com/Hjdskes/898cd7389b447f75c9ca0798097ac436

Jente Hidskes

Engineer

Nordic Payment Networks

+46728558908

Klarna Bank AB (publ)

Sveavägen 46, 111 34 Stockholm

Tel: +46 8 120 120 00

Reg no: 556737-0431

klarna.com




On Wed, Feb 9, 2022 at 11:12 AM Ján Osuský <jan.osusky at iblsoft.com> wrote:
>
> Hi Jente,
>
> we use libssh2 for a client implementation too and we use both the fingerprint (with libssh2_hostkey_hash) and the host key itself.
>
> Function "libssh2_session_hostkey" returns pointer to the key as expected, and also sets the key length and type.
>
> In our code (that is not new anymore) we still use libssh2_session_startup instead of libssh2_session_handshake but I don't think that should be a problem.
>
>
> Best regards,
>
>
> JanO
>
>
>
> On Wednesday 9. February 2022, 10:17:05 (+01:00), Jente Hidskes via libssh2-devel wrote:
>
> > Hey folks,
> >
> > I am working on a small SFTP client using libssh2. I would like for
> > this client to persist the host key of the server it is connecting to,
> > but I seem to be unable to get a hold of it.
> >
> > After initialising libssh2 and calling libssh2_session_handshake, I am
> > able to print the host key fingerprint through libssh2_hostkey_hash as
> > in the example programs. I assumed I would be able to print the actual
> > host key rather than the fingerprint with libssh2_session_hostkey, but
> > that returns an empty string.
> >
> > I suspect that libssh2_session_hostkey only returns the local host key
> > when operating as a server (given this[1] source code comment), but
> > the docs[2] are unclear about this: they just state "get the remote
> > key" and "returns a pointer to the current host key".
> >
> > Am I doing something wrong, or is it indeed impossible right now to
> > print the host key when operating as a client?
> >
> > Kind regards,
> >
> > Jente
> >
> > [1] https://github.com/libssh2/libssh2/blob/2a2aaed3b6c3c1dc25e35e11afcfb23f88a18510/src/libssh2_priv.h#L628
> > [2] https://www.libssh2.org/libssh2_session_hostkey.html
>