How to use licensecxx

Prerequisites

Licensecxx relies on nlohmann-json and OpenSSL. nlohmann/json is fetched through CMake-Fetchcontent during configure time and made available the library. Whether this is the preferrable way is still up to debate.

OpenSSL needs to be made available by the parent project/user. Licensecxx only calls FindPackage(OpenSSL). If that cannot find the OpenSSL 1.1 library, the licensecxx cannot be built.

Building

This project is supposed to be used as a library addition to your software. Licensecxx is CMake based and can be included as a submodule in your project. Including it as a subdirectory makes the licensecxx targets available to your project

The lcxx::identifiers library is optional to produce/verify identifying hash codes of the target machine.

Note that LCXX_NLOHMANN_JSON_CMAKE_FETCH can be explicitly turned off to prevent LCXX from downloading Nlohmann::Json using CMake Fetchcontent.

Generate a license

A simple license generator looks like this:

It prints a signed license json file to the file my-project-license.lic. This is similar to the sample [license_generator](samples/license_generator/main.cpp).

Verify a license

A generated license file or string can be loaded and verified provided a public key. Additional hardware identifiers can be checked against the currently running hardware.

int main()
{
    auto key                  = lcxx::crypto::load_key( some_pem_pem_key_rsa_string, lcxx::crypto::key_type::public_key );
    auto [license, signature] = lcxx::from_json( std::filesystem::path("my-project-license.lic") );

    if ( !lcxx::verify_license( license, signature, key ) ) {
        std::cout << "This program is not licensed!" << std::endl;
        return -1;
    }

    if ( lcxx::identifiers::verify( license.get( "hardware" ) ) ) {
        std::cout << "The hardware does not match the one licensed!" << std::endl;
        return -2;
    }

    return 0;
}

A similar sample is given in license_verifier

Further samples are given in the samples folder.

Generating a key pair

To generate an RSA key pair that can be processed by licensecxx the following openssl commands can be used:

These command generate a private-public key pair. Enabling the CMake option LCXX_GENERATE_KEYS will an additional CMake interface library called lcxx::key. Linking it will have CMake generate a key-pair from that through a simple python script two header files: - public_key.hpp - private_key.hpp

For that location of the generated private/public keys can be specified with the variables LCXX_PRIVATE_KEY / LCXX_PUBLIC_KEY. The key size defaults to 1024 but can be configured through LCXX_KEY_SIZE.

Finally, LCXX_KEY_HEADER_DIR defines the path where the generated header files should be located. It will automatically be part of the lcxx::key include directories.

Enabling LCXX_GENERATE_KEYS will require Python as a dependency for the header generation.