The class template cryptof_encryptor and cryptof_decryptor provide filtering API for encrypting/decrypting stream. References Crypto API on win32 and openssl on linux platform.
#include <boost/iostreams/filters/cryptof.hpp>
#include <fstream>
#include <iostream>
#include <boost/iostreams/filtering_streambuf.hpp>
#include <boost/iostreams/copy.hpp>
#include <boost/iostreams/filters/cryptof.hpp>
int main()
{
std::ifstream file("hello.txt", ios_base::in | ios_base::binary);
std::filtering_streambuf<input> in;
in.push(boost::iostreams::cryptof::cryptof_decryptor{"private_key.pem"});
in.push(file);
boost::iostreams::copy(in, cout);
}