Re: [Qemu-devel] spec, RFC: TLS support for NBD

[Florian Weimer <fweimer@redhat.com>]

On 10/20/2014 01:51 PM, Markus Armbruster wrote:
> Furthermore, STARTTLS is vulnerable to active attacks: if you can get
> between the peers, you can make them fall back to unencrypted silently.
> How do you plan to guard against that?

The usual way to deal with this is to use different syntax for 
TLS-enabled and non-TLS addresses (e.g., https:// and http://).  With a 
TLS address, the client must enforce that only TLS-enabled connections 
are possible.  STARTTLS isn't the problem here, it's just an accident of 
history that many STARTTLS client implementations do not require a TLS 
handshake before proceeding.

I cannot comment on whether the proposed STARTTLS command is at the 
correct stage of the NBD protocol.  If there is a protocol description 
for NBD, I can have a look.

-- 
Florian Weimer / Red Hat Product Security