Questions about generating keys

Oskar L. oskar at
Sat Aug 25 16:29:12 CEST 2007

> If I had good reason to believe Google was up to something nefarious,
> there is nothing in heaven or earth that would cause me to say "yes,
> that site is authentic."

The point of certificates is for you to be able to verify that you are on
the site you think you are, and not a fake one. If you go to,
and the certificate is ok, then the site is _authentic_. If the
certificate is not ok, then someone might have messed with your DNS
settings or hosts file, making go to the wrong IP, and the
site you get is then fake.

To say that a site isn't authentic because you don't trust the information
on it or the people that run it makes little sense. Does McDonald's not
have an authentic site because we don't believe them when they say their
food is healthy? Is politician X's site authentic because we agree with
him/her, but politician Y's is not, because we disagree with him/her?

Mallory might be a liar who you don't trust, but that does not mean that
it's impossible for anyone to authenticate that Mallory really is Mallory.
Mallory can never be unauthentic, only someone pretending to be her can.

> Trust is the ultimate dealbreaker.  Always has been, always will be.

Yes you can trust your friend Trevor, and yes weather you trust him or not
is the deal breaker. But you also need to authenticate him by some means.
Anyone can tell you they are Trevor. If you visit him authentication is
easy, you recognize him by his looks, the sound of his voice etc. Crypto
makes authentication over the Internet possible.

> Authentication in a nutshell, can be summed up in a single sentence.
> Unfortunately, you get two choices in how to finish it.
> I believe this thing to be authentic, because...
> 	* I just do, all right?
> 	* I note it has something authentic which vouches
> 	  for it.

"I just do, all right?"

That's not a good answer. It offers no facts or logical reasoning. If a
company tells you their products are the best, and you ask them why, would
you be satisfied if they answered "they just are, all right?"

"I believe X to be authentic, because I note it has Y which vouches for it."

That's logical reasoning, but leaves the question of why you trust Y

> Choose one of the two statements.  If you choose the latter, then
> continue the chain.

I would rather have:

-This thing is authentic, because I have verified it myself.

-I trust this thing, because someone I trust and have verified claims it
to be.

> Why is the signature authentic?  Because the key which made the
> signature is authentic.

Yes, that's logical.

> Why is the key which made the signature authentic?  Because a signature
> on that key is authentic.

No then it's only trusted. The signature on the key is authentic, yes, and
the public key you use to verify the signature is also authentic. But the
information, someone claiming that another a key is authentic, is only
trusted. You can't verify that your friend isn't lying to you by using any
kind of crypto. This is the weak link in the chain which brings everything
down to the level of trust.

The key would be authentic if you had verified it yourself.

> Why is the key which made the signature authentic?  Because that's
> John's own key.
> Why does that make the key authentic?  Because he just does, all right?

It doesn't. Verifying the fingerprint would make it authentic.

> Follow an authentication chain
> far enough and you will always, inevitably, reach trust, some level
> where the answer is "because I just do, all right?"

If there are other people besides yourself involved in the chain, and they
are providing information which you do not verify, only trust, then yes,
trust is the weakest point. But that does not mean that everything in the
chain is only trusted. Somewhere in the chain we could have 5+5=10, and we
do not need to trust this, we can be 100% sure of it.

> why trust is a necessary precondition for authentication.  Without it,
> everything falls apart.

You can trust Trevor, but this trust is useless if you have no way of
authenticating that Trevor really is Trevor.

Trust is not needed for authentication. You can authenticate a lot of
things just by looking at them, your friends for example.


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