WebApp Sec: Re: Article - A solution to phishing

[Rogan Dawes <discard () dawes za net>]

Adam Shostack wrote:

> | No. The user would install the certificate on their computer, and they
> | would then not need a username and password at all (other than a
> | passphrase to protect the prvate key on their local machine - the
> | passphrase is never entered on a remote site, and the private key itself
> | is never sent of the machine anyway).
> | 
> | Certificates are "the" solution to this problem. 
> | No, assuming the real bank is verifying the client certificate for all 
> | connections. It is impossible (without breaking SSL) to perform man in 
> | the middle attacks when both client and server are using certificates.
> Really?  It is impossible to perform a MITM if both sides are validating
> the certificates.  If you visit phisher.screwthemall.com and that
> site has a server cert signed by a CA installed in the browser, then
> phisher can just visit your bank, get the challenge bits, send them on
> to you, and then send your responses to your bank.  (I think.  Its
> still somewhat early, but I can't see why SSL would break in a user
> visible way here.)
I'm not entirely sure if you are agreeing or disagreeing with me here. 
Note that I said, if the connection is using mutually authenticated SSL 
(i.e. both client and server present certificates to each other), there 
is no way to MITM the connection, barring a cryptographic break of the 
SSL protocol itself.
For a detailed explanation, please see 
http://www.cgisecurity.com/owasp/html/ch07s04.html
The thing is, that if client certificates are used, nothing is ever 
typed into a site that a phisher could use to impersonate you. So, no 
phishing is possible.
> Shoot, a client implementation that, like SSH, remembered the banks
> cert, rather than throwing away that information in favor of a CA
> signature would improve things.
>
> Adam
And what would happen when the cert is renewed, as they are/should be on 
an annual basis?
That is why the CA process was designed, to allow for this sort of thing.

Nonetheless, I hear what you are saying. If the cert of a site that we 
have visited before changes, maybe a simple notification could be popped 
up. But then I question the value of this. What do we want the user to 
do? If this happens on a regular basis, with the various sites that they 
visit, they will simply learn to click OK.
And if they visit a phisher, who is using a different site name, with a 
different certificate, there will be nothing to compare with. This would 
only identify the case where a phisher has managed to obtain a CA-signed 
cert for the target server (www.mybank.com), managed to intercept your 
connection to the real mybank.com, and route it to their own servers.
If they have done that, there are bigger problems!!!!

Regards,

Rogan
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