Load OpenSSL custom engine in C/C++

Question

I'm creating a custom OpenSSL engine for an ARM board, to be used in applications that are already linking to libssl. However, I need to tell the application to load this custom engine and use it. I'm only able to find the command line for openssl. So the question is: how can I load an OpenSSL engine and use it in a C/C++ application?

Answer 1

Use ENGINE_by_id(...). You also might need to set OPENSSL_ENGINES environment variable to specify the path to the directory where your custom engine is located.

const char *engine_id = "your_custom_engine_id";

// ...

engine = ENGINE_by_id(engine_id);
if (engine == NULL) {
    // handle error
}

if (ENGINE_init(engine) == 0)  {
    // handle error
}

EVP_PKEY *evp_key = ENGINE_load_public_key(engine, key_uri, NULL, NULL);
if (evp_key == NULL) {
    // handle error
}