One of my roles at Mozilla is that I’m part of the Root Program team, which manages the list of trusted Certificate Authorities (CAs) in Firefox and Thunderbird. And, because we run our program in an open and transparent manner, other entities often adopt our trusted list.
In that connection, I’ve recently been the lead investigator into the activities of a Certificate Authority (CA) called WoSign, and a connected CA called StartCom, who have been acting in ways contrary to those expected of a trusted CA. The whole experience has been really interesting, but I’ve not seen a good moment to blog about it. Now that a decision has been taken on how to move forward, it seems like a good time.
The story started in late August, when Google notified Mozilla about some issues with how WoSign was conducting its operations, including various forms of what seemed to be certificate misissuance. We wrote up the three most serious of those for public discussion. WoSign issued a response to that document.
Further issues were pointed out in discussion, and via the private investigations of various people. That led to a longer, curated issues list and much more public discussion. WoSign, in turn produced a more comprehensive response document, and a “final statement” later.
One or two of the issues on the list turned out to be not their fault, a few more were minor, but several were major – and their attempts to explain them often only led to more issues, or to a clearer understanding of quite how wrong things had gone. On at least one particular issue, the question of whether they were deliberately back-dating certificates using an obsolete cryptographic algorithm (called “SHA-1”) to get around browser blocks on it, we were pretty sure that WoSign was lying.
Around that time, we privately discovered a couple of certificates which had been mis-issued by the CA StartCom but with WoSign fingerprints all over the “style”. Up to this point, the focus has been on WoSign, and StartCom was only involved because WoSign bought them and didn’t disclose it as they should have done. I started putting together the narrative. The result of those further investigations was a 13-page report which conclusively proved that WoSign had been intentionally back-dating certificates to avoid browser-based restrictions on SHA-1 cert issuance.
If you can write an enthralling page-turner about f**king certificate authorities doing scuzzy nerd sh*t, damn, I couldn't pull that off.
— SwiftOnSecurity (@SwiftOnSecurity) September 28, 2016
The report proposed a course of action including a year’s dis-trust for both CAs. At that point, Qihoo 360 (the Chinese megacorporation which is the parent of WoSign and StartCom) requested a meeting with Mozilla, which was held in Mozilla’s London office, and attended by two representatives of Qihoo, and one each from StartCom and WoSign. At that meeting, WoSign’s CEO admitted to intentionally back-dating SHA-1 certificates, as our investigation had discovered. The representatives of Qihoo 360 wanted to know whether it would be possible to disentangle StartCom from WoSign and then treat it separately. Mozilla representatives gave advice on the route which might most likely achieve this, but said that any plan would be subject to public discussion.
WoSign then produced another updated report which included their admissions, and which outlined a plan to split StartCom out from under WoSign and change the management, which was then repeated by StartCom in their remediation plan. However, based on the public discussion, the Mozilla CA Certificates module owner Kathleen Wilson decided that it was appropriate to mostly treat StartCom and WoSign together, although StartCom has an opportunity for quicker restitution than WoSign.
And that’s where we are now :-) StartCom and WoSign will no longer be trusted in Mozilla’s root store for certs issued after 21st October (although it may take some time to implement that decision).