BN_RAND(3ossl)

📦
version 15.1 · 2 versions
, in freebsd 15.1

🎀 BN_RAND(3ossl) 🎀

okay bestie, welcome to the BN_rand page from OpenSSL — yes, that OpenSSL. this is the one that teaches you how to conjure cryptographically strong pseudo-random numbers with BIGNUMs. no cap, it's lowkey iconic. 💅

✨ NAME ✨

BN_rand_ex, BN_rand, BN_priv_rand_ex, BN_priv_rand, BN_pseudo_rand, BN_rand_range_ex, BN_rand_range, BN_priv_rand_range_ex, BN_priv_rand_range, BN_pseudo_rand_range — the whole squad's job is literally to generate pseudo-random number. that's the gig. 🎲

🌸 SYNOPSIS 🌸

#include <openssl/bn.h>

int BN_rand_ex(BIGNUM *rnd, int bits, int top, int bottom,
               unsigned int strength, BN_CTX *ctx);
int BN_rand(BIGNUM *rnd, int bits, int top, int bottom);

int BN_priv_rand_ex(BIGNUM *rnd, int bits, int top, int bottom,
                    unsigned int strength, BN_CTX *ctx);
int BN_priv_rand(BIGNUM *rnd, int bits, int top, int bottom);

int BN_rand_range_ex(BIGNUM *rnd, const BIGNUM *range, unsigned int strength,
                     BN_CTX *ctx);
int BN_rand_range(BIGNUM *rnd, const BIGNUM *range);

int BN_priv_rand_range_ex(BIGNUM *rnd, const BIGNUM *range, unsigned int strength,
                          BN_CTX *ctx);
int BN_priv_rand_range(BIGNUM *rnd, const BIGNUM *range);
⚠️ heads up bestie: the following functions have been deprecated since OpenSSL 3.0, and can be hidden entirely by defining OPENSSL_API_COMPAT with a suitable version value, see openssl_user_macros(7):
int BN_pseudo_rand(BIGNUM *rnd, int bits, int top, int bottom);
int BN_pseudo_rand_range(BIGNUM *rnd, const BIGNUM *range);

🦋 DESCRIPTION 🦋

💖 the BN_rand_ex() of it all

BN_rand_ex() generates a cryptographically strong pseudo-random number of bits in length and security strength at least strength bits, using the random number generator for the library context associated with ctx. it stores the generated data in rnd. the parameter ctx may be NULL, in which case the default library context is used. 🫶

if bits is less than zero, or too small to accommodate the requirements specified by the top and bottom parameters, an error is returned — like, it's not gonna fake it for you, she's honest.

the top parameter specifies requirements on the most significant bit of the generated number:

  • BN_RAND_TOP_ANY — there is no constraint. live your truth, no rules. ✨
  • BN_RAND_TOP_ONE — the top bit must be one. periodt.
  • BN_RAND_TOP_TWO — the two most significant bits of the number will be set to 1, so that the product of two such random numbers will always have 2*bits length. math girlie behavior. 🧮💅

and for bottom:

  • BN_RAND_BOTTOM_ODD — the number will be odd.
  • BN_RAND_BOTTOM_ANY — it can be odd or even. chaotic neutral.
🫠 tiny lil catch: if bits is 1 then top cannot also be BN_RAND_TOP_TWO. that combo is a no.

BN_rand() is the same as BN_rand_ex() except that the default library context is always used.

💜 the range girlies

BN_rand_range_ex() generates a cryptographically strong pseudo-random number rnd, of security strength at least strength bits, in the range 0 <= rnd < range, using the random number generator for the library context associated with ctx. the parameter ctx may be NULL, in which case the default library context is used.

BN_rand_range() is the same as BN_rand_range_ex() except that the default library context is always used.

🔥 the private ones (iykyk)

BN_priv_rand_ex(), BN_priv_rand(), BN_priv_rand_rand_ex() and BN_priv_rand_range() have the same semantics as BN_rand_ex(), BN_rand(), BN_rand_range_ex() and BN_rand_range() respectively. they are intended to be used for generating values that should remain private, and mirror the same difference between RAND_bytes(3) and RAND_priv_bytes(3). 🤫

👑 NOTES 👑

always check the error return value of these functions and do not take randomness for granted — an error occurs if the CSPRNG has not been seeded with enough randomness to ensure an unpredictable byte sequence. 😭 like fr fr, check your return values, bestie, it's giving responsible main character energy.

⭐ RETURN VALUES ⭐

the functions return 1 on success, 0 on error. the error codes can be obtained by ERR_get_error(3). slay. ✅

🌈 SEE ALSO 🌈

🎀 HISTORY 🎀

  • starting with OpenSSL release 1.1.0, BN_pseudo_rand() has been identical to BN_rand() and BN_pseudo_rand_range() has been identical to BN_rand_range(). the BN_pseudo_rand() and BN_pseudo_rand_range() functions were deprecated in OpenSSL 3.0. 💀 rip bozo
  • the BN_priv_rand() and BN_priv_rand_range() functions were added in OpenSSL 1.1.1. 🦋
  • the BN_rand_ex(), BN_priv_rand_ex(), BN_rand_range_ex() and BN_priv_rand_range_ex() functions were added in OpenSSL 3.0. ✨

Copyright 2000-2022 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.

💖 and that's the whole page, bestie! this was OpenSSL 3.5.6, dated 2026-04-07 — the BN_RAND(3ossl) era. go forth and generate responsibly 🧚‍♀️✨
📦 where this page comes from