Browser Extension Defeats Internet Eavesdropping

Pickens writes to tell us that researchers at Carnegie Mellon University have created a simple system to help prevent man-in-the-middle attacks. Using a preset list of friendly sites called 'notaries,' the new 'Perspectives' system helps users to authenticate sites that require secure communications. Additionally this should help with the recently debated solution implemented by Firefox that has so many users frustrated and confused. "By independently querying the desired target site, the notaries can check whether each is receiving the same authentication information (a digital certificate), in response. If one or more notaries report authentication information that is different than that received by the browser or other notaries, a computer user would have reason to suspect that an attacker has compromised the connection."

Comments

Does not work if comprimised on site side

[TorKlingberg]

Interesting idea, but it will not work if the man-in-the-middle is hijacking the websites connection rather than the users.

But who trusts their notaries?

[querist]

The idea of "notaries" is essentially the same idea as having the Certificate Authorities: a third party who is considered trustworth and sufficiently dilligent that the third party would take the appropriate measures to verify something before signing off on it.

Who picks these people/companies?

Why not use a system like PGP, building a web of trust?

Disclaimer: I am a SC Notary Public.

Re:But who trusts their notaries?

[Tom]

I think the point is that a large-enough number of candidates plus a random selection equals statistical trust - the larger the base, the less likely it is that there isn't at least one uncompromised notary in your random sample.
A CA will always have the single-point-of-failure problem. While infiltrating Thawte certainly isn't something your average chinese hacker kid can do, it is certainly within the abilities of the NSA, or the KGB. The "web of trust" approach and the "we pick someone at random from a large crowd" approach both make it prohibitively expensive to compromise the sources of trust.

If you pick 5 sources at random, even from a crowd where 50% have been compromised, you still have a 1-(0.5^5) ~= 97% chance of having at least one uncompromised trust source. That's a pretty good record against an enemy who could compromise half of what could be millions of candidates.

Some many reasons this is a bad idea:

[keithadler]

1. Bringing down notaries would bring down all SSL/TLS traffic 2. Compromising the extension itself could allow for proxying of SSL traffic; exposing private information 3. Using the the notaries increases the footprint of SSL traffic; increasing the attack surface

Easy DoS Attack

[plsuh]

Folks,

Nice try, but this scheme is a bad idea. It opens up a really easy DoS attack. All the attacker has to do is present a bogus certificate or SSH host key to a quorum of the notaries. BAM -- the server is now blocked. In fact, if the attacker can do this over a sustained period, he can masquerade as the actual server.

There's a reason why PKI works the way it does. There's a reason why you should use certificates or key pairs for authentication. The proposed system doesn't really help. Given that you can get a real SSL certificate for $15/year these days, only laziness leads to the use of a self-signed certificate.

I read the darn paper (yeah, yeah, I know, this is Slashdot, I'm not supposed to do that). They have a DoS column in their table in the Security Analysis section but don't discuss DoS in the text at all. Notaries need to be well known and are thus obvious candidates for a DNS-based attack. Next!

--Paul