EVP_PKEY_COPY_PARAMETERS(3ossl)

💅 EVP_PKEY_COPY_PARAMETERS 💅

okay bestie, so this is the <openssl/evp.h> girlie of the OpenSSL manual, version 3ossl. She's here to explain public key parameter + comparison functions, and honestly? She ate. Let's get into it 🎀

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✨ NAME ✨

EVP_PKEY_missing_parameters, EVP_PKEY_copy_parameters, EVP_PKEY_parameters_eq, EVP_PKEY_cmp_parameters, EVP_PKEY_eq, EVP_PKEY_cmp — literally the public key parameter and comparison functions. That's the whole vibe. 🦋

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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);

okay so, heads up — these next two have been deprecated since OpenSSL 3.0 😭 and you can hide them entirely by defining OPENSSL_API_COMPAT with a suitable version value, check openssl_user_macros(7) for the details:

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. no cap, that's it.
• EVP_PKEY_copy_parameters() — copies the parameters from key from to key to. an error is returned 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 match? this function literally has no effect. it's giving "nothing to do here" 💀
• EVP_PKEY_parameters_eq() — checks the parameters of keys a and b for equality. slay.
• EVP_PKEY_eq() — checks the keys a and b for equality, including their parameters if they're available. main character energy, she checks everything 👑

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🦋 NOTES 🦋

okay so 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 — important!! they're aliases for EVP_PKEY_eq() and EVP_PKEY_parameters_eq().

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 not rely on public key comparison alone. periodt. 🙈

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. 💜
• EVP_PKEY_copy_parameters() returns 1 for success and 0 for failure. simple as that.
• 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

fr fr memorize those four numbers, they will come up. 🔥

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🌈 SEE ALSO 🌈

• EVP_PKEY_CTX_new(3)
• EVP_PKEY_keygen(3)

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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(). out with the old, in with the iconic ✨

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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>.

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and that's the whole page bestie 🫶 this one's from version 3.5.6, dated 2026-04-07, and it's still EVP_PKEY_COPY_PARAMETERS(3ossl) through and through. mwah 💋