Friday, December 18, 2015

PKI reforms starts. Kind of.

Microsoft has lost faith in more than 20 CAs.

Still this is a partial measure. The chain is as strong as its weakest link is. If we have a web server certificate, signed by CA X , whose CA certificate is issued / signed by (trusted) root CA R, the X can be the weakest link, and no Microsoft measures will help prevent this link to be broken. This is exactly what happened in previous cases, when sub-CAs (like those X) issued certificates in violation to PKI rules and practices.

The solution? Web of trust. This would require certain modifications of the PKI, but the requirement for the end-entity certificate to be signed by at least two CAs would eliminate most issues related to wrongdoing by sub-CAs. Look - if you are an attacker and you hijack CA X , there's little use in this - you would need to hijack CA Y and/or CA Z . This is possible, but much more complicated and imposes higher risks to your attack to you.

In general there's much there that can be borrowed from OpenPGP. CA (Issuer) can still be present in the certificate, but there can be other extensions like subsignatures or counter-certificates included, and that would significantly increase the protection level.

Wednesday, December 16, 2015

A "fatal flaw" which is neither a fatal, nor a flaw.

The article in SC Magazine talks about "security flaws" in Kerberos protocol.  But what are those flaws about?

If we dig deeper, the only phrase in the article suggests that "if the attacker knows user's secret key, he can replay authentication without the need for user's password". Actually this is not a flaw. If the attacker got to user's secret key somehow, the user and the network are already in trouble, because this means that the attacker has already found some flaws elsewhere.

Now, Kerberos' shortcomings and disadvantages were known for years, and the discussed one was known as well. This is why Kerberos is not recommended and is replaced by modern protocols like SAML and OAuth even in intranets.

To sum it up, digging the grave and finding old flaws and bringing them back to the sunlight is an easy way to establish yourself as a security researcher, but you still need to look at the roots. And protection of credentials and use of multifactor authentication are the things that separate good security from the bad one.