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 option was added in OpenSSL 3.4.

       By  specifying the enable-fips-jitter configuration option, the FIPS provider will use an internal jitter
       source for its entropy.  Enabling this option will cause the FIPS provider to operate in a  non-compliant
       mode  unless  an  entropy assessment ESV <https://csrc.nist.gov/Projects/cryptographic-module-validation-
       program/entropy-validations>          and          validation          through          the          CMVP
       <https://csrc.nist.gov/projects/cryptographic-module-validation-program>   are   additionally  conducted.
       This option was added in OpenSSL 3.5.

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>.

3.5.0                                              2025-06-04                              EVP_RAND-JITTER(7SSL)