William Arbaugh  wrote:
>David Wagner writes:
>> As for remote attestion, it's true that it does not directly let a remote
>> party control your computer.  I never claimed that.  Rather, it enables
>> remote parties to exert control over your computer in a way that is
>> not possible without remote attestation.  The mechanism is different,
>> but the end result is similar.
>If that is the case, then strong authentication provides the same 
>degree of control over your computer. With remote attestation, the 
>distant end determines if they wish to communicate with you based on 
>the fingerprint of your configuration. With strong authentication, the 
>distant end determines if they wish to communicate with you based on 
>your identity.

I must confess I'm puzzled why you consider strong authentication
the same as remote attestation for the purposes of this analysis.

It seems to me that your note already identifies one key difference:
remote attestation allows the remote computer to determine if they wish
to speak with my machine based on the software running on my machine,
while strong authentication does not allow this.

As a result, remote attestation enables some applications that strong
authentication does not.  For instance, remote attestation enables DRM,
software lock-in, and so on; strong authentication does not.  If you
believe that DRM, software lock-in, and similar effects are undesirable,
then the differences between remote attestation and strong authentication
are probably going to be important to you.

So it seems to me that the difference between authenticating software
configurations vs. authenticating identity is substantial; it affects the
potential impact of the technology.  Do you agree?  Did I miss something?
Did I mis-interpret your remarks?

P.S. As a second-order effect, there seems to be an additional difference
between remote attestation ("authentication of configurations") and
strong authentication ("authentication of identity").  Remote attestation
provides the ability for "negative attestation" of a configuration:
for instance, imagine a server which verifies not only that I do have
RealAudio software installed, but also that I do not have any Microsoft
Audio software installed.  In contrast, strong authentication does
not allow "negative attestation" of identity: nothing prevents me from
sharing my crypto keys with my best friend, for instance.

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