Use OpenSSL for crypto

[chadbrewbaker]

Is there an engineering reason why OpenSSL was not used? The biggest portability pain right now for gg is the crypto libraries.

I'm noodling on a PR to use OpenSSL and zstd for better portability and to reduce the IO of thunks over the network.

[keithw]

I think the only crypto in the project is for computing the SHA-256; if you're able to submit an elegant wrapper around OpenSSL that computes the SHA-256 of a C++ string and switches the dependency, I expect it would be favorably received! (As you probably are also aware, OpenSSL does not have the greatest track record as far as security goes, and the APIs are pretty byzantine, but I agree it is much more widely available.)

I'd be curious about the actual benefits of zstd over zlib (and if there are any portability concerns of note), but at least for me I don't have a strong preference either way.