- NAME
- DESCRIPTION

- Identity
- Supported parameters

- NOTES
- EXAMPLES
- SEE ALSO
- COPYRIGHT

# 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 EVP_RAND(3)/PARAMETERS.

# 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), EVP_RAND(3)/PARAMETERS

# 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.