NAME

       EVP_RAND-JITTER - The randomness seed source EVP_RAND implementation

DESCRIPTION

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

       This software seed source produces randomness based on tiny CPU "jitter" fluctuations.

       It is available when OpenSSL is compiled with enable-jitter option. When available it is listed in
       openssl list -random-generators and openssl info -seeds.

   Identity
       "JITTER" 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, "JITTER", NULL);
        EVP_RAND_CTX *rctx = EVP_RAND_CTX_new(rand, NULL);

       The enable-jitter configuration option was added in OpenSSL 3.4.

EXAMPLES

        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, "JITTER", 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);

SEE ALSO

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

COPYRIGHT

       Copyright 2024 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>.

3.4.1                                              2025-04-03                              EVP_RAND-JITTER(7SSL)