The Grymoire Blog

Here is a summary of the DigiNotar hack that has been in the news.

DigiNotar is a Dutch Certificate Authority (CA).  They provide a root certificate installed in your IE, Firefox, Safari or Chrome web browser. They are one of several hundred Certificate Authorities.

First of all, someone noticed someone was able to create an unauthorized  Google certificate. The certificate was for “*.google.com” and allowed anyone using it to perform a Man-in-the-Middle (MITM) attack.  Essentially, someone could intercept any secure traffic to and from Google (Gmail, etc.) It was spotted by someone in Iran Someone in Iran noticed this. The Google certificate was signed by DigiNotar, which was unusual, as Google uses a different CA. This sort of activity would be notices if you had installed a browser add-on like Firefox’s Certificate Patrol.

This created quite a bit of news, similar to the Comodo Hack.  According to the Associated Press, “DigiNotar acknowledged it had been hacked in July, though it didn’t disclose it at the time. It insisted as late as Tuesday that its certificates for government sites had not been compromised.” And “But Donner said a review by an external security company had found DigiNotar’s government certificates were in fact compromised, and the government is now taking control of the company’s operations. The government also is trying to shift over to other companies that act as digital notaries, he said.”

It is then revealed  that there were 531 forged certificates created, targeting CIA, Yahoo, Twitter, Facebook, WordPress, Microsoft Live, torproject, Mozilla, Skype, and others.

The root certificate to DigiNotar was revoked by Microsoft, Google (Chrome), and Mozilla (Firefox). Firefox was updated to 6.0.2 to address this.

It turns out that someone who calls themselves the ComodoHacker claims to have hacked Comodo and DigiNotar. The hacker has bragged about his intentions in his Pastebin account. Some of his comments

• He is an independent hacker, and not part of an Iranian Cyber Army
• He is a hactivist – he hacks for his own reasons
• He hacked DigiNotar because of their involvement in the Srebrenica genocide 16 years ago.
• He’s protesting “US and Israel’s involvement in Stuxnet”
• He’s protesting HBGary’s CEO for spreading malware in the Middle East, and that the FBI did not “see/find/detect/catch” this.
• He has hacked 4 other CA’s and names one: GlobalSign. In response GlobalSign stopped issuing certificates
• He claims he has hacked Microsoft’s update process. For proof, he has created a modified version of calc.exe that is “signed by Microsoft.”

There is a discussion if this person is really him. We shall see.

Expect more news. Many security experts have stated that the entire Certificate Structure infrastructure is broken.  Having 100+ Certificate Authorities – all trusted equally, is just a bad idea. This is the opposite of Defense in Depth, where you need multiple failures to compromise a system. If any CA fails, the entire system fails. Let’s compare the two approaches mathematically.

Suppose you had a system where each certificate was signed by two certificate authorities. For the sake of simplification, let’s assign a probability of a certificate compromise to be 1%. Perhaps it should be 0.1%, but we can look at that later.

In the case of two CA’s signing each certificate, the probability of a certificate compromise is -(CA¹)*(CA²), or in this case (1%*1%)  or 0.01%.

Compare this to the case where you have ten CA’s, and if ANY are compromised, any certificate may be suspect.

To calculate the probability of a certificate compromise with multiple equivalent CA’s, you need the formula

1-(1-CA¹)*(1-CA²)*(1-CA³)*(1-CA⁴)*(1-CA⁵)*(1-CA⁶)*(1-CA⁷)*(1-CA⁸)…*(1-CA^N)

If there are 10 CA’s, and each has a probability of 1% failure, then the probability of a failure if any are compromised is

1-(99%*99%*99%*99%*99%*99%*99%*99%*99%*99%),

which is

1-0.99¹⁰  => 1-0.90438 or about 10%

If you had a hundred CA’s, then the chance of a failure is 1-0.99¹⁰⁰ or 1-0.3660 or 73%!

Suppose you change the percentage to 0.1% per CA. 0.999¹⁰⁰ is 90.4%, so the change of any single certificate being compromised is 10%.

If you assume is 0.01% per individual CA, the probability becomes 1%.

In any case, the proliferation of CA’s in the browser has seriously broken Internet Security. This is why people and teams like CMU and Moxie Marlinspike to offer suggestions.