Re: OpenSSL 3.0.0 custom entropy source

Dr Paul Dale <pauli@xxxxxxxxxxx> · Tue, 14 Sep 2021 09:00:06 +1000

Try working from providers/implementations/rands/seed_src.c  You'll need 
to reimplement seed_src_generate() to use your RNG.

To use your custom seed source, you can either use the OpenSSL 
configuration file to set a "random" section that includes a "seed" 
setting or you can call RAND_set_seed_source_type() early in your 
startup sequence.

Pauli

On 14/9/21 8:19 am, Kory Hamzeh wrote:
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