EVP_PKEY_COPY_PARAMETERS(3ossl)

💅 EVP_PKEY_COPY_PARAMETERS(3ossl) — bestie's guide to public key parameters & comparison

okay so this is an OpenSSL man page, the manual name is EVP_PKEY_COPY_PARAMETERS(3ossl) and it's genuinely so useful — it covers all the public key parameter and comparison functions. no cap, once you get these you're kinda set. ✨

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🌸 NAME 🌸

EVP_PKEY_missing_parameters, EVP_PKEY_copy_parameters, EVP_PKEY_parameters_eq, EVP_PKEY_cmp_parameters, EVP_PKEY_eq and EVP_PKEY_cmp — the public key parameter and comparison functions, aka the whole lil squad 🫶

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✨ SYNOPSIS ✨

#include <openssl/evp.h>

int EVP_PKEY_missing_parameters(const EVP_PKEY *pkey);
int EVP_PKEY_copy_parameters(EVP_PKEY *to, const EVP_PKEY *from);

int EVP_PKEY_parameters_eq(const EVP_PKEY *a, const EVP_PKEY *b);
int EVP_PKEY_eq(const EVP_PKEY *a, const EVP_PKEY *b);

and, sadly, the deprecated ones 🥲 — they've been deprecated since OpenSSL 3.0 and you can hide them entirely by defining OPENSSL_API_COMPAT with a suitable version value, see openssl_user_macros(7):

int EVP_PKEY_cmp_parameters(const EVP_PKEY *a, const EVP_PKEY *b);
int EVP_PKEY_cmp(const EVP_PKEY *a, const EVP_PKEY *b);

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💖 DESCRIPTION 💖

• EVP_PKEY_missing_parameters() — returns 1 if the public key parameters of pkey are missing, and 0 if they're present or the algorithm doesn't use parameters. simple as that 💅
• EVP_PKEY_copy_parameters() — copies the parameters from key from to key to. it returns an error if the parameters are missing in from, or present in both from and to and they mismatch. and if the parameters in from and to are both present and they match? this function literally has no effect. it just vibes. 🦋
• EVP_PKEY_parameters_eq() — checks the parameters of keys a and b for equality. 🎀
• EVP_PKEY_eq() — checks the keys a and b for equality, including their parameters if they're available. the full vibe check, not just the surface level 🔥

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🧚 NOTES 🧚

the main purpose of EVP_PKEY_missing_parameters() and EVP_PKEY_copy_parameters() is to handle public keys in certificates where the parameters are sometimes omitted from a public key if they're inherited from the CA that signed it. iykyk 😌

the deprecated EVP_PKEY_cmp() and EVP_PKEY_cmp_parameters() differ in their return values compared to other _cmp() functions — plot twist. they're aliases for EVP_PKEY_eq() and EVP_PKEY_parameters_eq(). 💀

the function EVP_PKEY_cmp() previously only checked the key parameters (if there are any) and the public key, assuming that there always was a public key and that private key equality could be derived from that. but because it's no longer assumed that the private key in an EVP_PKEY(3) is always accompanied by a public key, the comparison can't rely on public key comparison alone. the audacity, honestly 😭

instead, EVP_PKEY_eq() (and therefore also EVP_PKEY_cmp()) now compares:

1. the key parameters (if there are any) ⭐
2. the public keys or the private keys of the two EVP_PKEYs, depending on what they both contain 👑

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🌈 RETURN VALUES 🌈

EVP_PKEY_missing_parameters() returns 1 if the public key parameters of pkey are missing and 0 if they're present or the algorithm doesn't use parameters. (yes, it's the same sentence as in DESCRIPTION — iconic consistency 💖)

EVP_PKEY_copy_parameters() returns 1 for success and 0 for failure. 🫶

and the comparison girlies — EVP_PKEY_cmp_parameters(), EVP_PKEY_parameters_eq(), EVP_PKEY_cmp() and EVP_PKEY_eq() — return:

• 1 if their inputs match ✅
• 0 if they don't match ❌
• -1 if the key types are different 🙈
• -2 if the operation is not supported 🚫

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🦋 SEE ALSO 🦋

EVP_PKEY_CTX_new(3), EVP_PKEY_keygen(3) — go read those next bestie, they're lowkey essential 💜

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👑 HISTORY 👑

• The EVP_PKEY_cmp() and EVP_PKEY_cmp_parameters() functions were deprecated in OpenSSL 3.0. 🥀
• The EVP_PKEY_eq() and EVP_PKEY_parameters_eq() were added in OpenSSL 3.0 to replace EVP_PKEY_cmp() and EVP_PKEY_cmp_parameters(). the glow-up was real ✨

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🍓 COPYRIGHT 🍓

Copyright 2006-2021 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>.

fr fr read the license before you go copy-pasting, bestie — it's giving "respect the icon" energy 💅

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okay that's the whole page, mwah 💋 this was OpenSSL 3.5.0, dated 2026-09-25, titled EVP_PKEY_COPY_PARAMETERS(3ossl) — go forth and compare your keys responsibly, ily 🎀💖