Re: Clarification

The MITM attack can only succeed on the initial one time negotiation of
credentials.  Easily resolved by installing the key first.  I recommend
sneakernet, it's what I use.

Regardless, a DRM negotiation should/would be resolved after the trust
relationship has been established by the page negotiation.  So a
vulnerability exists if that process is flawed, but it isn't the ssh MITM
threat.


On Tue, May 14, 2013 at 2:49 AM, Henri Sivonen <hsivonen@iki.fi> wrote:

> On Tue, May 14, 2013 at 12:01 AM, Rick <graham.rick@gmail.com> wrote:
> > UA's gain a level of trust with me by publishing their source so that it
> can
> > be vetted by the community at large.  I don't trust them blindly.
> > Publishing the source for CDM's would make it less threatening.  I see no
> > reason why this can't be done; ssh is open, and more secure for having
> > published source.
>
> ssh is a bad analog, because the trust assumptions are different. When
> Alice uses ssh to connect to sshd on Bob's server, the adversary is
> neither Alice nor Bob but Cecil who is a MITM on the network and
> controls neither the computer running ssh nor the computer running
> sshd.
>
> In the DRM case, Alice runs a CDM in order to watch movies to which
> Cecil own the copyright from a streaming service operated by Bob. The
> adversary is Alice, so the CDM runs on a computer controlled by the
> adversary. This makes the requirements for the CDM fundamentally
> different from the requirements for ssh.
>
> But despite ssh being an inapplicable analog, in theory, it would be
> possible to publish the source code of the CDM except for the CDM's
> private key assuming that there exists a sufficiently strongly
> obfuscating compiler that can obfuscate both the binary and the
> runtime memory layout of the program. The source code of the compiler
> could be published, too, if the ways the obfuscation functions work
> can be parameterized from a random number generator. However, Alice
> cannot be allowed to perform the CDM the build process. The CDM needs
> to be built by someone that Cecil trusts to perform the build process
> using the published compiler, the published CDM source and a
> cryptographically strong random number generator for parametrizing the
> compiler and for generating the CDM private key. That is, the source
> disclosure would not involve the downstream freedoms associated with
> Open Source.
>
> Don't hold your breath for the source for Hollywood-approved CDMs
> being available without an NDA, though. Even though what I said in the
> previous paragraph could work in theory, publishing the source code
> for the CDM makes developing the obfuscating compiler postulated in
> the previous paragraph a more difficult engineering undertaking than
> developing an obfuscating compiler that may rely on the secrecy of the
> CDM source code.
>
> --
> Henri Sivonen
> hsivonen@iki.fi
> http://hsivonen.iki.fi/
>



-- 

Liked it, shared it, gave a thumbs up to the great JC and moved on in a
smooth and efficient ballet of holy surfing designed to bring glory to the
lord and spread bad spelling and grammar to the filthy masses.

Amen.