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.
EVP_RAND *rand = EVP_RAND_fetch(NULL, "SEED-SRC", NULL); EVP_RAND_CTX *rctx = EVP_RAND_CTX_new(rand);
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);
Licensed under the Apache License 2.0 (the ``License''). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.