In that case, the Signal protocol is open source. https://github.com/WhisperSystems/libsignal-protocol-c https://github.com/WhisperSystems/libsignal-protocol-c

In that case, the Signal protocol is open source. https://github.com/WhisperSystems/libsignal-protocol-c https://github.com/WhisperSystems/libsignal-protocol-c https://github.com/WhisperSystems/libsignal-protocol-java https://github.com/WhisperSystems/libsignal-protocol-java More generally (i.e. not for messaging apps), libsodium is great for application-layer cryptography: https://download.libsodium.org/doc/bindings_for_other_languages/index.html https://download.libsodium.org/doc/bindings_for_other_langua...