BN_CTX_NEW(3ossl)

💅 BN_CTX_NEW — the 3ossl glow-up

okay bestie so this is the OpenSSL manpage for BN_CTX_NEW(3ossl) — like, the family of functions that allocate and free BN_CTX structures. it's giving "small file, big lore" and honestly you're gonna eat this up ✨

🌸 NAME

BN_CTX_new_ex, BN_CTX_new, BN_CTX_secure_new_ex, BN_CTX_secure_new, BN_CTX_free — allocate and free BN_CTX structures. that's the whole job. slay 🫶

✨ SYNOPSIS

#include <openssl/bn.h>

BN_CTX *BN_CTX_new_ex(OSSL_LIB_CTX *ctx);
BN_CTX *BN_CTX_new(void);

BN_CTX *BN_CTX_secure_new_ex(OSSL_LIB_CTX *ctx);
BN_CTX *BN_CTX_secure_new(void);

void BN_CTX_free(BN_CTX *c);

💖 DESCRIPTION

okay so first of all, what even is a BN_CTX? it's a structure that holds BIGNUM temporary variables used by library functions. and the reason it exists is genuinely iconic: dynamically allocating memory to create BIGNUMs is rather expensive when you're doing it alongside repeated subroutine calls. so the BN_CTX structure is used instead. it's the group chat of temp variables, fr fr.

• BN_CTX_new_ex() — allocates and initializes a BN_CTX structure for the given library context ctx. the ctx value may be NULL, in which case the default library context will be used. no cap.
• BN_CTX_new() — the same as BN_CTX_new_ex() except that the default library context is always used. literally the same but simpler.
• BN_CTX_secure_new_ex() — allocates and initializes a BN_CTX structure but uses the secure heap (see CRYPTO_secure_malloc(3)) to hold the BIGNUMs, for the given library context ctx. the ctx value may be NULL, in which case the default library context will be used. it's giving extra security, extra care 💜
• BN_CTX_secure_new() — the same as BN_CTX_secure_new_ex() except that the default library context is always used.
• BN_CTX_free() — frees the components of the BN_CTX and the structure itself. and here's the part you gotta remember: since BN_CTX_start() is required in order to obtain BIGNUMs from the BN_CTX, in most cases BN_CTX_end() must be called before the BN_CTX may be freed by BN_CTX_free(). if c is NULL, nothing is done — she's unbothered, she's at peace 🧚

⚠️ warning bestie: a given BN_CTX must only be used by a single thread of execution. no locking is performed, and the internal pool allocator will not properly handle multiple threads of execution. so do NOT share one across threads, that's not the vibe, that's a bug 💀

🎀 RETURN VALUES

BN_CTX_new() and BN_CTX_secure_new() return a pointer to the BN_CTX. if the allocation fails, they return NULL and sets an error code that can be obtained by ERR_get_error(3). so check your return value, always, periodt.

BN_CTX_free() has no return values. she simply leaves 😭

💀 REMOVED FUNCTIONALITY

void BN_CTX_init(BN_CTX *c);

BN_CTX_init() is no longer available as of OpenSSL 1.1.0. applications should replace use of BN_CTX_init with BN_CTX_new instead:

BN_CTX *ctx;
ctx = BN_CTX_new();
if (!ctx)
    /* error */
...
BN_CTX_free(ctx);

like, she's gone, but her replacement ate 🔥

🌈 SEE ALSO

ERR_get_error(3), BN_add(3), BN_CTX_start(3)

👑 HISTORY

BN_CTX_init() was removed in OpenSSL 1.1.0. that's the whole history section and honestly? iconic brevity.

🍓 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>.

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and that's the whole page bestie 🫶 this was OpenSSL 3.5.0, dated 2026-09-25, filed under BN_CTX_NEW(3ossl) — go forth and free your contexts 💖✨