DH_GENERATE_KEY(3ossl)

💖 DH_GENERATE_KEY 💖

okay bestie, welcome to the DH_GENERATE_KEY(3ossl) page from the OpenSSL manual set — yes the whole trio lives here, no cap 🎀

✨ NAME ✨

DH_generate_key, DH_compute_key, DH_compute_key_padded — the lil squad that performs a Diffie-Hellman key exchange 💅

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🌸 SYNOPSIS 🌸

#include <openssl/dh.h>

⚠️ heads up bestie: the functions below have been deprecated since OpenSSL 3.0, and they can be hidden entirely by defining OPENSSL_API_COMPAT with a suitable version value, see openssl_user_macros(7).

int DH_generate_key(DH *dh);

int DH_compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh);

int DH_compute_key_padded(unsigned char *key, const BIGNUM *pub_key, DH *dh);

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🦋 DESCRIPTION 🦋

All of the functions described on this page are deprecated. Like, all of them. Every single one 😭 Applications should instead use EVP_PKEY_derive_init(3) and EVP_PKEY_derive(3) — that's the glow-up, fr fr.

DH_generate_key() does the first step of a Diffie-Hellman key exchange, by generating private and public DH values. Then, by calling DH_compute_key() or DH_compute_key_padded(), those get combined with the other party's public value to compute the shared key. it's giving teamwork, it's giving ✨collaboration✨.

DH_generate_key() expects dh to contain the shared parameters dh->p and dh->g. It generates a random private DH value unless dh->priv_key is already set, and computes the corresponding public value dh->pub_key, which can then be published. main character energy honestly 👑

DH_compute_key() computes the shared secret from the private DH value in dh and the other party's public value in pub_key, and stores it in key. key must point to DH_size(dh) bytes of memory. The padding style is RFC 5246 (8.1.2) that strips leading zero bytes. It is not constant time, due to the leading zero bytes being stripped. The return value should be considered public. 💀

DH_compute_key_padded() is similar but stores a fixed number of bytes. The padding style is NIST SP 800-56A (C.1) that retains leading zero bytes. It is constant time, due to the leading zero bytes being retained. The return value should be considered public. slay 🫶

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🌈 RETURN VALUES 🌈

• DH_generate_key() returns 1 on success, 0 otherwise.
• DH_compute_key() returns the size of the shared secret on success, -1 on error.
• DH_compute_key_padded() returns DH_size(dh) on success, -1 on error.

The error codes can be obtained by ERR_get_error(3). go get 'em 🔥

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💜 SEE ALSO 💜

EVP_PKEY_derive(3), DH_new(3), ERR_get_error(3), RAND_bytes(3), DH_size(3)

iykyk, these are the besties you'll be hanging out with 💖

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🎀 HISTORY 🎀

• DH_compute_key_padded() was added in OpenSSL 1.0.2.
• All of these functions were deprecated in OpenSSL 3.0.

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⭐ COPYRIGHT ⭐

Copyright 2000-2021 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>.

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and that's the whole page bestie, you ate it up 💅✨

this lil masterpiece is from OpenSSL version 3.5.9, dated 2026-09-29 — DH_GENERATE_KEY(3ossl), no cap 🦋🌸 bye pookie, go derive some keys (with EVP_PKEY_derive tho, remember? deprecated 🙈)