Support for GnuTLS or OpenSSL

[bkmgit]

Would you consider pull requests to also supporting GnuTLS or OpenSSL?

[mierenhoop]

Maybe. Can you elaborate on why you think it's a good idea to add them?

The only reason I can think of is for not requiring MbedTLS installed alongside what's already on the system, which we can alternatively achieve by vendoring the used parts of MbedCrypto.

Two other possible advantages of would be portability and performance, but 1. MbedTLS is very portable by itself and 2. MbedTLS is not used for expensive cryptography here.

If we do go through with it, I will impose some constraints:

• MbedTLS/OpenSSL/GnuTLS specific implementations are each in their own source file, implementing a set of generic functions.

• They don't change the current omemo* API.

• They don't introduce opaque data to the omemoSession and omemoStore structures.

• They don't rely on global state (in our code at least, I think MbedTLS does internally have some global state for custom allocators).

• They don't introduce ownership lifetimes that exist in between omemo* function calls, that for example require something like "omemoFreeSession()".

[mierenhoop]

OpenSSL support is now in the develop branch (https://github.com/mierenhoop/picomemo/blob/develop/openssl.c). I'm satisfied with how it turned out, so it will probably be in a release soon.

[bkmgit]

Thanks. Testing it out, this will be very helpful for GNU/Linux packaging without bundling the other libraries.

[mierenhoop]

Okay, understandable that supporting OpenSSL is preferred when targeting Linux systems.

There are more (build related) changes on the way to support dynamic linking, notably making the callbacks not unresolved and splitting the two OMEMO versions into separate headers. Currently the code is hostile to dynamic linking.

[bkmgit]

It builds for me, though is helpful to add -fPIC as a build flag. Will sonames be supported in the shared libraries? If so, will the sonames follow the versioning scheme used in the releases?

[mierenhoop]

I have added -fPIC and soname. The soname will follow the major version of the releases, is that how it's supposed to be done?

[bkmgit]

Soname is usually used to indicate breaking changes in the library api when the major soname version changes. Using the version number is reasonable, though you can choose other options if desired.