Re: [Trans] draft-linus-trans-gossip-ct-01 doesn't work

[Tom Ritter <[e-mail]>]

On 26 March 2015 at 09:56, Watson Ladd <[e-mail]> wrote:
> Dear all,
>
> Suppose I can consistently redirect a client C to a masquerading
> server M. The proposed gossip mechanism will not detect this, as SCTs
> are only ever sent back to the server they are received from. This
> should be fixed by having clients gossip constantly about STHs, thus
> ensuring that if any honest server is contacted, the MITM is detected.

If you are able to isolate a client from a resource _forever_ then
yes, you can win. You can also stop the client from receiving browser
updates, from contacting a client's trusted auditor (if they have
one), from receiving operating system updates, trust root updates, and
so on.

An attacker who can isolate a client from a resource once and forever
is exceptionally difficult to defend against.  It's not clear (to me
at least) what a browser could even do in that situation except refuse
to work at all.  (And I'll note that unless I'm mistaken, every
browser chooses to go the other way and actually fail _open_, removing
security mechanisms if it's been unable to update for a long time.)

-tom