BN_MOD_INVERSE(3ossl)

💖 BN_MOD_INVERSE 💖

okay bestie, so this is an OpenSSL page, from the 3ossl manual set, and it's all about one little function that does modular inverse math. it's giving number theory but make it cute. let's go 🧚✨

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✨ NAME ✨

BN_mod_inverse — compute inverse modulo n 🎀

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🌸 SYNOPSIS 🌸

#include <openssl/bn.h>

BIGNUM *BN_mod_inverse(BIGNUM *r, BIGNUM *a, const BIGNUM *n,
                       BN_CTX *ctx);

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🦋 DESCRIPTION 🦋

so like. BN_mod_inverse() computes the inverse of a modulo n and drops the result into r, and the whole vibe is:

(a*r)%n==1

that's it, that's the math 💅

if r is NULL, no worries, a brand new BIGNUM gets created for you. main character energy, honestly.

ctx is a previously allocated BN_CTX that gets used for temporary variables — it's the backstage crew making the magic happen 🫶

and here's the cute part: r may be the same BIGNUM as a. they can share. iconic.

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💀 NOTES 💀

bestie. listen. it is an error to use the same BIGNUM as n. like, do not do that. that's the one thing. n stays in its own lane, no sharing with n, periodt 🚫

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🔥 RETURN VALUES 🔥

BN_mod_inverse() returns the BIGNUM containing the inverse 💖 and returns NULL on error 😭

you can grab the error codes with ERR_get_error(3) if you need the receipts.

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👑 SEE ALSO 👑

• ERR_get_error(3)
• BN_add(3)

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🌈 COPYRIGHT 🌈

Copyright 2000-2017 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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okay that's the whole page, you ate it fr fr 💅✨ this was BN_MOD_INVERSE(3ossl) from version 3.5.9, dated 2026-09-29 — mwah, go compute some inverses bestie 🎀🦋💜