EVP_RAND-SEED-SRC(7ossl)

🌸 NAME 🌸

This is the 7ossl manual page for EVP_RAND-SEED-SRC — the randomness seed source EVP_RAND implementation, bestie. 💖

🦋 DESCRIPTION 🦋

okay so this whole page is about support for deterministic random number generator seeding through the EVP_RAND API. That's the vibe. ✨

The seed sources used get specified when OpenSSL is configured for building, using the --with-rand-seed= option. By default, operating system randomness sources are used. No cap. 💅

💅 Identity 💅

The name for this implementation is "SEED-SRC", and it can be used with the EVP_RAND_fetch() function. Periodt. 👑

🎀 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 this:

EVP_RAND *rand = EVP_RAND_fetch(NULL, "SEED-SRC", NULL);
EVP_RAND_CTX *rctx = EVP_RAND_CTX_new(rand, NULL);

🔥 EXAMPLES 🔥

Example time, bestie — here's the full code block, iconic and intact:

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, "SEED-SRC", 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 💖

Legal tea time 🍵 — keep this exactly as it is:

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>.

---

xoxo, bestie 💖 — this was OpenSSL 3.5.6, dated 2026-04-07, signing off from the 7ossl manual. Slay. ✨