RSA_CHECK_KEY(3SSL)

📦
version 4.0.3 · 14 versions
, in ubuntu stonking

💖 RSA_CHECK_KEY(3SSL) 💖

ok so bestie, welcome to the RSA_check_key page from the OpenSSL manuals. Two functions, one big job: validating private RSA keys. Let's get into it ✨

🌸 NAME 🌸

RSA_check_key_ex, RSA_check_key — validate private RSA keys 💅

✨ SYNOPSIS ✨

okay so first you gotta pull in the header:

#include <openssl/rsa.h>

now the tea ☕ — the following functions have been deprecated since OpenSSL 3.0, and you can hide them entirely by defining OPENSSL_API_COMPAT with a suitable version value. check out openssl_user_macros(7) for that.

int RSA_check_key_ex(const RSA *rsa, BN_GENCB *cb);

int RSA_check_key(const RSA *rsa);

🦋 DESCRIPTION 🦋

so like… both of the functions on this page are deprecated, fr fr 😭. Applications should instead use EVP_PKEY_public_check(3), EVP_PKEY_private_check(3) and EVP_PKEY_pairwise_check(3). periodt.

RSA_check_key_ex() does the actual validating of RSA keys. here's the vibe check it runs 👑:

  • it checks that p and q are in fact prime
  • and that n = p*q

it does not work on RSA public keys that have only the modulus and public exponent elements populated. not it 🙈

it also checks that d*e = 1 mod (p-1*q-1), and that dmp1, dmq1 and iqmp are set correctly or are NULL.

it performs integrity checks on all the RSA key material, so the RSA key structure must contain all the private key data too. therefore, it cannot be used with any arbitrary RSA key object — even if it is otherwise fit for regular RSA operation. that's just how it is bestie 💀

the cb parameter is a callback that will be invoked in the same manner as BN_is_prime_ex(3).

RSA_check_key() is equivalent to RSA_check_key_ex() with a NULL cb. literally the same thing, just without the callback 🎀

💜 RETURN VALUES 💜

  • RSA_check_key_ex() and RSA_check_key() return 1 if rsa is a valid RSA key, and 0 otherwise.
  • they return -1 if an error occurs while checking the key.
if the key is invalid or an error occurred, the reason code can be obtained using ERR_get_error(3). go get that error code bestie, it's giving detective energy 🔍

💀 BUGS 💀

ngl, there's some mess here. a method of verifying the RSA key using opaque RSA API functions might need to be considered. right now RSA_check_key() simply uses the RSA structure elements directly, bypassing the RSA_METHOD table altogether — and completely violating encapsulation and object-orientation in the process 😭 iconic behaviour honestly.

the best fix will probably be to introduce a "check_key()" handler to the RSA_METHOD function table so that alternative implementations can also provide their own verifiers. someone tell the maintainers 🫶

🌈 SEE ALSO 🌈

🎀 HISTORY 🎀

  • all of these functions were deprecated in OpenSSL 3.0.
  • RSA_check_key_ex() appeared after OpenSSL 1.0.2.

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>.

and that's the whole page bestie!! 🌸 this was version 4.0.3, dated 2026-09-29, straight from the OpenSSL crew. stay validated, stay prime, mwah 💋✨🦋

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