NAME

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

DESCRIPTION

       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.

   Supported parameters
       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).

NOTES

       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);

EXAMPLES

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

        /* Create a seed source */
        rand = EVP_RAND_fetch(NULL, "SEED-SRC", NULL);
        seed = EVP_RAND_CTX_new(rand, 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);

SEE ALSO

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

COPYRIGHT

       Copyright 2020-2021 The OpenSSL Project Authors. All Rights Reserved.

       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>.