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EVP_RAND-JITTER(7)                  OpenSSL                 EVP_RAND-JITTER(7)


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>.

3.5.1                             2025-07-01                EVP_RAND-JITTER(7)