OpenSSL 3.0.0 custom entropy source

[Kory Hamzeh]

Hi,

We are upgrading from OpenSSL 1.0.1g+OpenSSL-FIPS-2.0.5 to 3.0.0. Yes, I know, big jump. We have our own entropy source we use to seed the OpenSSL DRBG. This is a basic code snippet of how we set it up:

        DRBG_CTX *dctx = FIPS_get_default_drbg();
        FIPS_drbg_init(dctx, NID_aes_256_ctr, DRBG_FLAG_CTR_USE_DF);
        FIPS_drbg_set_callbacks(dctx,
                                                   rand_get_entropy,
                                                  rand_free_entropy,
                                                  0,
                                                  rand_get_entropy,
                                                  rand_free_entropy);


Error checking has been removed in the example for the sake of brevity.

I am trying to figure out  how to implement this with OpenSSL 3. From what I have read in the docs, I need to create a rand provider. But I still feel like I don’t understand how it all fit together. I did look at fuzz_rand.c and fake_rand.c, and if I understood everything correctly, neither of them use an external entropy/seed source.

Are there better examples of what I am looking for?

Thanks,
Kory