A single key is used both to encrypt/sign and verify/decrypt messages. For this reason, it is critical to keep the key confidential.
let key_data =[64,33,195,234,107,63,107,237,113,199,
183,130,203,194,247,31,76,51,203,163,
126,238,206,125,225,74,103,105,133,181,
61,189];
let key = libhydrogen::secretbox::Key::from(key_data);
let context = libhydrogen::secretbox::Context::default();
let ciphertext = libhydrogen::secretbox::encrypt(b"hello world", 1, &context, &key);
let decrypted = libhydrogen::secretbox::decrypt(&ciphertext, 1, &context, &key).unwrap();
println!("{}", String::from_utf8(decrypted).unwrap());