Are WoSign S/MIME certificates generated on the server side and therefore unsafe to use?

Question

WoSign has been in the media for offering free server and client certificates. Since one of my (free) S/MIME certificate from another CA is about to expire soon after one year and WoSign offers certificates, which are valid for thee years, I applied for their certificate, because I hoped to be able to skip the re-creation of new certificates in the next years.

During the process I wondered, why there was no indication from my browser, that it was creating a key pair, as I am used to from my last applications at different CAs. When the process was finished, a PFX file was offered for download. No need to export the certificate from the browser certificate storage.

According to their policy (in chapter 3.2.1), they offer to generate a private key for their subscribers. I understand, that this should be avoided, because nobody except the owner should ever be in possession of a private key. While they state, that subscribers may also choose to create own private keys and CSRs for server certificates, they don't make any statement about creating the private key for client certificate in another way.

Is my assumption correct, that the private keys used for their client certificates are really created on the server side, and is it correct, that (while they claim they don't) they could keep it and use it to decrypt/sign messages, exactly as the subscribers could do with their certificate? This should be totally unacceptable, because one would have to trust them, that they delete the private key, that they should not even had in the first place. But since I was unable to find any criticism about such an issue with their client certificate issuing process, I might have gotten something wrong.

Answer 1

These certificates are of very little value. First of all, allowing them to generate the private key is very questionable. We have no details on how they do this or whether they retain this information - for all we know, they use the same private key for all certs or retain the key information, which may not be done in a secure manner (imagine what a rich target that datbase would be!).

the other problem with this service is that it has very weak vetting processes. The only real benefit of using a certificate service is to give your certificate an additional level of trust. If I receive an email or visit a site with a certificate, the degree to which I will trust that certificate is determined by the level of trust I have in the issuing authority. Certificates issue by this 'authority' have an extremely low level of trust because the issuer does not do any real vetting to ensure the certificate is being issued to the 'real' site or address owner.

Essentially, all this service is doing is making it easy for someone to get a certificate who doesn't want to learn how to create their own certificate using something like pgp. Of course, certificates you create yourself don't have much trust, but that is why you would normally grow that trust through key signing parties or using a recognised CA which does adequate vetting. Combine that with the fact you don't know who has access to the private key (assuming you allow the site to generate that data) and the certs provided by this service are possibly even less trustworthy than even a self signed certificate.