[pedrocr]

Isn't that just because PKCS#11 is an in-process API so not really meant for calls over a socket? So wouldn't you need to actually write a PKCS#11 compliant library to plug into the server, a software HSM and then some form of serializing protocol to talk between the two? Or is there a standard way to do PKCS#11 over a socket? A quick look at the spec made it look like a "here's how our struct's are packed" kind of standard.

[remosi]

Yup, that pretty much sums it up. I'm currently trying to figure out if dbus could be that serialisation since it takes care of a reasonable amount of the hard work for you. But I'm no expert on GObject, so slow going. (Also, I'm not sure that I'm the best person to be writing this... I don't really have that much security knowledge, I just spent a whole pile of time trying to figure out how to secure my (client) keys recently and wondered why we didn't do something sensible for server keys.

[pedrocr]

In that case why not skip the middle man and just implement enough soft-HSM for whatever Apache/nginx needs with a simple serialization protocol just for that? Emulating all of PKCS#11 sounds like a chore for very little gain.

[remosi]

Having looked at PKCS#11, I'm not sure what bits you could get away with not implementing. It does have functions for things like "get random bytes", which I guess you might not want, but that's just barely any code: (int get_random_bytes() { return CKR_NOT_SUPPORTED; }).

All the complexity in this proposal is the serialisation/deserialisation which is about the same amount of work if it's pkcs#11 or some custom thing.

Custom API: Pro: Marginally simpler to implement. Pro: If the webserver fork()'s it by default, then more users get the benefit for the case that you can read the webserver memory. Con: Doesn't protect against attacks that can read files readably by the webserver. Con: Becomes complicated when you want to move to a real HSM. Con: Isn't reusable between webservers, let alone for your mail server, xmpp server, webbrowsers, ssh clients and so on.

Using PKCS#11: Pro: Can start with a PKCS#11 softhsm running as a seperate user today, migrate to hardware HSM with little change tomorrow. Pro: Reusable across multiple webservers, already usable by browsers and ssh clients. Pro: A well defined, maintained, open standard with a wide variety of implementations that already exist. Con: Slightly more complex than a custom protocol, but I'd argue that the custom protocol would grow to cover at least what PKCS#11 supports. I'm currently investigating using dbus for the protocol, so serialisation/deserialisation is mostly taken care of.

Am I missing some Pro for a custom protocol?

[pedrocr]

>Con: Doesn't protect against attacks that can read files readably by the webserver.

This isn't a con for the custom API, it's a con for a forking solution instead of a serialization between two different users.

If PKCS#11 is indeed a good fit for that protocol then it's indeed a much better solution that something custom for the reasons you mention. Good luck with the implementation.