RAND_ADD(3ossl)

hey bestie 💖 this is the RAND_ADD(3ossl) page from OpenSSL, and it's all about how to add randomness to the PRNG or get its status. The whole squad is RAND_add, RAND_poll, RAND_seed, RAND_status, RAND_event, RAND_screen, and RAND_keep_random_devices_open — yes, that's a lot of names, but we got this ✨

🌸 NAME 🌸

RAND_add, RAND_poll, RAND_seed, RAND_status, RAND_event, RAND_screen, RAND_keep_random_devices_open — add randomness to the PRNG or get its status. periodt 💅

✨ SYNOPSIS ✨

#include <openssl/rand.h>

int RAND_status(void);
int RAND_poll();

void RAND_add(const void *buf, int num, double randomness);
void RAND_seed(const void *buf, int num);

void RAND_keep_random_devices_open(int keep);

The following functions have been deprecated since OpenSSL 1.1.0, and can be hidden entirely by defining OPENSSL_API_COMPAT with a suitable version value, see openssl_user_macros(7):

int RAND_event(UINT iMsg, WPARAM wParam, LPARAM lParam);
void RAND_screen(void);

🦋 DESCRIPTION 🦋

okay so these functions seed the random generator and check whether it's seeded enough. And lowkey? Manually (re-)seeding the default OpenSSL random generator (RAND_OpenSSL(3)) is generally not necessary (but it is allowed), because it (re-)seeds itself automatically using trusted system entropy sources. That holds unless the default RAND_METHOD has been replaced, or OpenSSL was built with automatic reseeding disabled — see RAND(7) for more details.

RAND_status() is the vibe check: it tells you whether or not the random generator has been sufficiently seeded. If it hasn't, functions such as RAND_bytes(3) will fail. no cap.

RAND_poll() uses the system's capabilities to seed the random generator using random input obtained from polling various trusted entropy sources. The default choice of the entropy source can be modified at build time, see RAND(7) for more details.

RAND_add() mixes the num bytes at buf into the internal state of the random generator. Usually you won't need this function, as mentioned above. The randomness argument is an estimate of how much randomness is contained in buf, in bytes, and should be a number between zero and num. Want the literature on sources of randomness and how to estimate their randomness? For example: [NIST SP 800-90B]. The content of buf cannot be recovered from subsequent random generator output. Applications that intend to save and restore random state in an external file should consider using RAND_load_file(3) instead. that's the move 💅

NOTE: In FIPS mode, random data provided by the application is not considered to be a trusted entropy source. It is mixed into the internal state of the RNG as additional data only and this does not count as a full reseed. For more details, see EVP_RAND(7).

RAND_seed() is equivalent to RAND_add() with randomness set to num. iconic shortcut, honestly.

RAND_keep_random_devices_open() controls file descriptor usage by the random seed sources. Some seed sources maintain open file descriptors by default, which allows such sources to operate in a chroot(2) jail without the associated device nodes being available. When the keep argument is zero, this call disables the retention of file descriptors. Conversely, a nonzero argument enables the retention of file descriptors. This function is usually called during initialization and it takes effect immediately. This capability only applies to the default provider. periodt.

RAND_event() and RAND_screen() are equivalent to RAND_poll() and exist for compatibility reasons only. HISTORY has the receipts below.

🎀 RETURN VALUES 🎀

Here's the tea on return values ☕

• RAND_status() — returns 1 if the random generator has been seeded with enough data, 0 otherwise.
• RAND_poll() — returns 1 if it generated seed data, 0 otherwise.
• RAND_event() — hands you back RAND_status().
• the other functions — they do not return values. literally nothing. 💀

🫶 SEE ALSO 🫶

You'll want to check these next: RAND_bytes(3), RAND_egd(3), RAND_load_file(3), RAND(7), EVP_RAND(7). go off, bestie 📚✨

😭 HISTORY 😭

RAND_event() and RAND_screen() were deprecated in OpenSSL 1.1.0 and should not be used. so yeah, don't use them — that's the whole history lesson 💀

👑 COPYRIGHT 👑

Copyright 2000-2020 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>.

This page is from OpenSSL 3.5.0, dated 2026-09-25 — mwah 💋✨