X509_VERIFY(3ossl)

💖 X509_VERIFY 💖 — the 3ossl one, bestie

okay so this is the OpenSSL page about checking signatures on certs, cert requests, CRLs and attribute certs. it's giving "trust but verify" but make it ✨cryptographic✨.

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✨ NAME ✨

X509_verify, X509_self_signed, X509_REQ_verify_ex, X509_REQ_verify, X509_CRL_verify, X509_ACERT_verify — verify certificate, certificate request, or CRL signature. yes bestie, that's the whole vibe check 💅

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🌸 SYNOPSIS 🌸

#include <openssl/x509.h>

int X509_verify(X509 *x, EVP_PKEY *pkey);
int X509_self_signed(X509 *cert, int verify_signature);

int X509_REQ_verify_ex(X509_REQ *a, EVP_PKEY *pkey, OSSL_LIB_CTX *libctx,
                       const char *propq);
int X509_REQ_verify(X509_REQ *a, EVP_PKEY *r);
int X509_CRL_verify(X509_CRL *a, EVP_PKEY *r);

#include <openssl/x509_acert.h>
int X509_ACERT_verify(X509_CRL *a, EVP_PKEY *r);

not me pointing out that X509_ACERT_verify() is declared with an X509_CRL *a — that's literally what the page says, so we're keeping it character for character, no notes 🙈

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🦋 DESCRIPTION 🦋

X509_verify() verifies the signature of certificate x using public key pkey. and that's it. that's the whole thing. only the signature is checked — no other checks (such as certificate chain validity) are performed. so like, don't come for it asking about the chain, it simply does not do that 💀

X509_self_signed() checks whether certificate cert is self-signed. for it to succeed, the issuer and subject names must match, the components of the authority key identifier (if present) must match the subject key identifier, etc. the signature itself is actually verified only if verify_signature is 1, because for explicitly trusted certificates this verification is not worth the effort. lowkey relatable — why do extra work for someone you already trust 🫶

X509_REQ_verify_ex(), X509_REQ_verify(), X509_CRL_verify() and X509_ACERT_verify() verify the signatures of certificate requests, CRLs and attribute certificates respectively. one function per friend group, we love an organized roster ✨

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👑 RETURN VALUES 👑

X509_verify(), X509_REQ_verify_ex(), X509_REQ_verify() and X509_CRL_verify() return 1 if the signature is valid and 0 if the signature check fails. if the signature could not be checked at all — because it was ill-formed, the certificate or the request was not complete, or some other error occurred — then -1 is returned. three possible outcomes, truly the main character energy of error handling 😭

X509_self_signed() returns the same values but also returns 1 if all respective fields match and verify_signature is 0. no cap.

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🎀 SEE ALSO 🎀

• d2i_X509(3)
• ERR_get_error(3)
• X509_CRL_get0_by_serial(3)
• X509_get0_signature(3)
• X509_get_ext_d2i(3)
• X509_get_extension_flags(3)
• X509_get_pubkey(3)
• X509_get_subject_name(3)
• X509_get_version(3)
• X509_NAME_ENTRY_get_object(3)
• X509_NAME_get_index_by_NID(3)
• X509_NAME_print_ex(3)
• X509V3_get_d2i(3)
• X509_verify_cert(3)
• OSSL_LIB_CTX(3)

go read those too, bestie, it's a whole syllabus 🦋

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⭐ HISTORY ⭐

X509_verify(), X509_REQ_verify(), and X509_CRL_verify() are available in all versions of OpenSSL. they've been here since forever, actual icons 👑

X509_REQ_verify_ex(), and X509_self_signed() were added in OpenSSL 3.0. glow-up era ✨

X509_ACERT_verify() was added in OpenSSL 3.4. the newest baby of the family 🍓

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🌈 COPYRIGHT 🌈

Copyright 2015-2024 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, you're literally a cert-verifying genius now 💅✨

this was version 3.5.9, dated 2026-09-29, from the X509_VERIFY(3ossl) page — mwah, go forth and verify responsibly, bestie 🫶💖🌸🦋🎀