EVP_RAND-SEED-SRC - The randomness seed source EVP_RAND implementation

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       <https://www.openssl.org/source/license.html>.

3.5.0                                              2025-06-04                            EVP_RAND-SEED-SRC(7SSL)

       Support for deterministic random number generator seeding through the EVP_RAND API.

       The seed sources used are specified at the time OpenSSL is configured for building using the
       --with-rand-seed= option.  By default, operating system randomness sources are used.

   Identity
       "SEED-SRC" is the name for this implementation; it can be used with the EVP_RAND_fetch() function.

   Supportedparameters
       The supported parameters are:

       "state" (OSSL_RAND_PARAM_STATE) <integer>
       "strength" (OSSL_RAND_PARAM_STRENGTH) <unsigned integer>
       "max_request" (OSSL_RAND_PARAM_MAX_REQUEST) <unsigned integer>
           These parameters work as described in "PARAMETERS" in EVP_RAND(3).

        EVP_RAND *rand;
        EVP_RAND_CTX *seed, *rctx;
        unsigned char bytes[100];
        OSSL_PARAM params[2], *p = params;
        unsigned int strength = 128;

        /* Create and instantiate a seed source */
        rand = EVP_RAND_fetch(NULL, "SEED-SRC", NULL);
        seed = EVP_RAND_CTX_new(rand, NULL);
        EVP_RAND_instantiate(seed, strength, 0, NULL, 0, NULL);
        EVP_RAND_free(rand);

        /* Feed this into a DRBG */
        rand = EVP_RAND_fetch(NULL, "CTR-DRBG", NULL);
        rctx = EVP_RAND_CTX_new(rand, seed);
        EVP_RAND_free(rand);

        /* Configure the DRBG */
        *p++ = OSSL_PARAM_construct_utf8_string(OSSL_DRBG_PARAM_CIPHER,
                                                SN_aes_256_ctr, 0);
        *p = OSSL_PARAM_construct_end();
        EVP_RAND_instantiate(rctx, strength, 0, NULL, 0, params);

        EVP_RAND_generate(rctx, bytes, sizeof(bytes), strength, 0, NULL, 0);

        EVP_RAND_CTX_free(rctx);
        EVP_RAND_CTX_free(seed);

       EVP_RAND-SEED-SRC - The randomness seed source EVP_RAND implementation

       A context for the seed source can be obtained by calling:

        EVP_RAND *rand = EVP_RAND_fetch(NULL, "SEED-SRC", NULL);
        EVP_RAND_CTX *rctx = EVP_RAND_CTX_new(rand, NULL);

EVP_RAND(3), "PARAMETERS" in EVP_RAND(3)