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EVP_RAND-SEED-SRC(7SSL)                        OpenSSL                       EVP_RAND-SEED-SRC(7SSL)



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>.



3.0.2                                        2026-04-07                      EVP_RAND-SEED-SRC(7SSL)