[iheartmemcache]

libsodium is pretty GPG compatible. Diffie-Hellman key exchange function[X25519]: int crypto_scalarmult(unsigned char q, const unsigned char n, const unsigned char p);

crypto_secretbox_easy() for both encrypting + signing in the traditional public-key fashion. AES-256-GCM is there for symmetric sessions. Even OTP's are supported. I don't think there's the full PKI/WoT implementation in there, at the moment, but it's definitely sufficient to do most of the heavy lifting.

(N.b. the documentation is only like 70 pages long, read the relevant sections on: sodium_memzero(), sodium_mlock(), the notes on VMs, the notes if you have swapon, the notes on disabling coredumps, don't use malloc, use sodium_malloc() (and with that, the appropriate padding precautions should be taken if you use sodium_allocarray()), and source your entropy properly. All of this is covered in the API guide. Consult it, because I'm likely misremembering one or two things.)