In https://postgr.es/m/69db7657-3f9d-4d30-8a4b-e06034251...@yesql.se 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).
It is a drop-in replacement for the OpenSSL code, and supports all the same features and options, except for two things: compression is not supported and the CRL cannot be loaded from a plain PEM file. A Keychain must be used for that instead. Current state ============= The frontend and backend are implemented more or less fully, the two main things missing being the CRL support (further details below) and loading DH files (to support the GUC added in c0a15e07cd). All non-CRL tests but one are passing. The failing test is in the frontend and it also fails when running against an OpenSSL backend, but I can’t find where the logic is flawed and could do with some help there. Threads ======= Just like the CFLocaleCopyCurrent() call referenced in postmaster.c, the Secure Transport APIs makes the process multithreaded. To keep this out of the postmaster, and contained in the backend, I’ve moved all functionality to open_server and left init empty. I could definitely need some clues on how to properly handle this, or if it’s a complete showstopper. 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. 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. The backend is only supporting PEM files at this point. Once we have support for Keychains, we can however use them for additionally supporting other Secure Transport features like OCSP etc. “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. Certificate Revocation ====================== Secure Transport supports loading CRL lists into Keychain files, the command line certtool can for example do that. When doing the trust evaluation on the connection, a policy can be added which enables revocation checking via CRL. I have however been unable to figure out how to load a CRL list programmatically, and as far as I can tell there is no API for this. The certtool utility is using the low-level CSSM APIs for this it seems, but adding that level of complexity doesn’t seem worth it for us to maintain (I did a test and it turned big, ugly and messy). Unless someone knows how to implement this, we’d be limited to requiring the use of a Keychain file for CRL support. This would break drop-in replacement support, but supporting certificate revocation seems more important. Platform Support ================ I’ve tested this on 10.11 El Capitan and 10.12 Sierra, which are the systems I have access to. Supporting prairiedog and dromedary in the buildfarm will probably be too hard (if at all possible), but down to 10.9 Mavericks should be quite possible (if someone has the required systems to test on). It adds a dependency on Core Foundation on top of Secure Transport, no other macOS APIs are used. Testing ======= In order to test this we need to provide an alternative to the openssl calls in src/test/ssl/Makefile for Secure Transport. On top of that, code to generate Keychains is required. The certtool application can do all the Keychain generations (I think) but this is still left open. The main thing to figure out here is how to avoid having to type in the Keychain password in a modal GUI that Secure Transport pops up. Since a Keychain can be passwordless it should be doable, but the right certtool incantations for that is still evading me. I’ve included a show-and-tell patch for this which I’ve used locally for testing during hacking. 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 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. Patches ======= 0001 - Adds support for running the SSL tests against another set of server binaries. This is only useful for testing during the implementation of a new SSL library, but then it’s crucial. Nothing Secure Transport specific in this patch. 0002 - Secure Transport fronten and backend as well as required scaffolding for building and a new GUC to show the current backend. securetransport_test.diff - Some ugly hacks I’ve used for testing, included as a show-and-tell, not for any form of submission. This leaves quite a few open questions that I hope to get some feedback on, and some code issues which I’d love eyes/hacking on. Do we still want this, and if so how to handle that we can’t be fully drop-in compatible with OpenSSL with regards to using a PEM file only configuration? Should we support PEM files at all in the backend or only Keychains? Another option could be to support PKCS12 files instead of (or additionally to) PEM since there is likely to be API support for loading PKCS12 and they can afaik contain CRLs. How can we ensure that new parameters hopefully covers more libraries than just Secure Transport? cheers ./daniel
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