What libraries to use for encryption?

Question

C++ / C#

Good afternoon! Yesterday I learned with regret that Qt (I have v5.4.1) is very limited in the capabilities of the cryptographic sdk, there is no way to work with standard encryption algorithms out of the box. In this regard, questions:
1. Maybe I'm looking in the wrong place? Point to the true path
2. If I looked there and still there is no full-fledged cryptographic sdk, what should I use for encryption - decryption? What cross-platform libraries to use?
Thank you.

Answer 1

OpenSSL

Answer 2

www.cryptopp.com