Open Stack

What you describe (at least the use case) seems to resemble
https://review.openstack.org/#/c/456394/ This work never moved
anywhere since the spec was posted though. You may want to revive the
discussion in scope of the spec.

Ihar

On Fri, Sep 29, 2017 at 12:21 PM, Giuseppe de Candia
<giuseppe.decandia at gmail.com> wrote:
> Hi Folks,
>
>
>
> My intent in this e-mail is to solicit advice for how to inject SSH host
> certificates into VM instances, with minimal or no burden on users.
>
>
>
> Background (skip if you're already familiar with SSH certificates): without
> host certificates, when clients ssh to a host for the first time (or after
> the host has been re-installed), they have to hope that there's no man in
> the middle and that the public key being presented actually belongs to the
> host they're trying to reach. The host's public key is stored in the
> client's known_hosts file. SSH host certicates eliminate the possibility of
> Man-in-the-Middle attack: a Certificate Authority public key is distributed
> to clients (and written to their known_hosts file with a special syntax and
> options); the host public key is signed by the CA, generating an SSH
> certificate that contains the hostname and validity period (among other
> things). When negotiating the ssh connection, the host presents its SSH host
> certificate and the client verifies that it was signed by the CA.
>
>
>
> How to support SSH host certificates in OpenStack?
>
>
>
> First, let's consider doing it by hand, instance by instance. The only
> solution I can think of is to VNC to the instance, copy the public key to my
> CA server, sign it, and then write the certificate back into the host (again
> via VNC). I cannot ssh without risking a MITM attack. What about using Nova
> user-data? User-data is exposed via the metadata service. Metadata is
> queried via http (reply transmitted in the clear, susceptible to snooping),
> and any compute node can query for any instance's meta-data/user-data.
>
>
>
> At this point I have to admit I'm ignorant of details of cloud-init. I know
> cloud-init allows specifying SSH private keys (both for users and for SSH
> service). I have not yet studied how such information is securely injected
> into an instance. I assume it should only be made available via ConfigDrive
> rather than metadata-service (again, that service transmits in the clear).
>
>
>
> What about providing SSH host certificates as a service in OpenStack? Let's
> keep out of scope issues around choosing and storing the CA keys, but the CA
> key is per project. What design supports setting up the SSH host certificate
> automatically for every VM instance?
>
>
>
> I have looked at Vendor Data and I don't see a way to use that, mainly
> because 1) it doesn't take parameters, so you can't pass the public key out;
> and 2) it's queried over http, not https.
>
>
>
> Just as a feasibility argument, one solution would be to modify Nova compute
> instance boot code. Nova compute can securely query a CA service asking for
> a triplet (private key, public key, SSH certificate) for the specific
> hostname. It can then inject the triplet using ConfigDrive. I believe this
> securely gets the private key into the instance.
>
>
>
> I cannot figure out how to get the equivalent functionality without
> modifying Nova compute and the boot process. Every solution I can think of
> risks either exposing the private key or vulnerability to a MITM attack
> during the signing process.
>
>
>
> Your help is appreciated.
>
>
>
> --Pino
>
>
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