Re: Support for Secure Transport SSL library on macOS as OpenSSL alternative

From: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>
To: Daniel Gustafsson <daniel(at)yesql(dot)se>, PostgreSQL mailing lists <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Support for Secure Transport SSL library on macOS as OpenSSL alternative
Date: 2017-08-03 11:06:28
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On 08/03/2017 01:02 PM, Daniel Gustafsson wrote:
> In I
> presented a WIP patch for adding support for the Apple Secure Transport SSL
> library on macOS as, an alternative to OpenSSL. That patch got put on the
> backburner for a bit, but I’ve now found the time to make enough progress to
> warrant a new submission for discussions on this (and hopefully help hacking).


> Keychains
> =========
> The frontend has support for using PEM files for certificates and keys. It can
> also look up the key for the certificate in a Keychain, or both certificate and
> key in a Keychain. The root certificate is still just read from a PEM file.

Why can't you have the root certificate in the keychain, too? Just not
implemented yet, or is there some fundamental problem with it?

> The existence of an sslcert config trumps a keychain, but when a keychain is
> used I’m currently using the sslcert parameter (awaiting a discussion on how to
> properly do this) for the certificate label required to search the keychain.
> There is a new frontend parameter called “keychain” with which a path to a
> custom Keychain file can be passed. If set, this Keychain will be searched as
> well as the default. If not, only the default user Keychain is used. There is
> nothing that modifies the Keychain in this patch, it can read identities
> (certificates and its key) but not alter them in any way.

OpenSSL also has a mechanism somewhat similar to the keychain, called
"engines". You can e.g. keep the private key corresponding a certificate
on a smart card, and speak to it with an OpenSSL "smart card reader"
engine. If you do that, the 'sslkey' syntax is "<engine name>:<key
name>". Perhaps we should adopt that syntax here as well? For example,
to read the client certificate from the key chain, you would use libpq
options like "keychain=/home/heikki/my_keychain

> “keychain” is obviously a very Secure Transport specific name, and I personally
> think we should avoid that. Any new configuration added here should take
> future potential implementation into consideration such that avoid the need for
> lots of backend specific knobs. “sslcertstore” comes to mind as an
> alternative, but we’d also need parameters to point into the certstore for
> finding what we need. Another option would be to do a URL based scheme
> perhaps.

I wouldn't actually mind using implementation-specific terms like
"keychain" here. It makes it clear that it's implementation-specific. I
think it would be confusing, to use the same generic option name, like
"sslcertstore", for both a macOS keychain and e.g. the private key store
in Windows. Or GNU Keyring. In the worst case, you might even have
multiple such "key stores" on the same system, so you'd anyways need a
way to specify which one you mean.

Actually, perhaps it should be made even more explicit, and call it
"secure_transport_keychain". That's quite long, though.

Wrt. keychains, is there a system-global or per-user keychain in macOS?
And does this patch use them? If you load a CRL into a global keychain,
does it take effect?

> Testing
> =======
> In order to test this we need to provide an alternative to the openssl calls in
> src/test/ssl/Makefile for Secure Transport.

Those openssl commands are only needed to re-generate the test
certificates. The certificates are included in the git repository, so
you only need to re-generate them if you want to modify them or add new
ones. I think it's OK to require the openssl tool for that, it won't be
needed just to run the test suite.

> Documentation
> =============
> I have started fiddling with this a little, but to avoid spending time on the
> wrong thing I have done very little awaiting the outcome of discussions here.
> I have tried to add lots of comments to the code however, to explain the quirks
> of Secure Transport.

I think this patch in general is in very good shape, and the next step
is to write the documentation. In particular, I'd like to see
documentation on how the keychain stuff should work. It'll be easier to
discuss the behavior and the interactions, once it's documented.

In fact, better to write the documentation for that now, and not bother
to change the code, until after we've discussed and are happy with the
documented behavior.

> I went into this thinking I would write a README for how to implement a new SSL
> library. But in the end, turns out the refactoring that went into our SSL code
> earlier made that part almost too easy to warrant that. It’s really quite
> straightforward.

That's nice to hear!

- Heikki

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