X509_VERIFY(3)

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

SYNOPSIS
 #include <openssl/x509.h>

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

DESCRIPTION
X509_verify() verifies the signature of certificate x using public key pkey. Only the signature is checked: no other checks (such as certificate chain validity) are performed.

X509_self_signed() checks whether certificate cert is self-signed. For success 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, as for explicitly trusted certificates this verification is not worth the effort.

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.

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.

X509_self_signed() returns the same values but also returns 1 if all respective fields match and verify_signature is 0.

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)

HISTORY
The X509_verify(), X509_REQ_verify(), and X509_CRL_verify() functions are available in all versions of OpenSSL.

X509_REQ_verify_ex(), and X509_self_signed() were added in OpenSSL 3.0.

X509_ACERT_verify() was added in OpenSSL 3.4.

X509_self_signed() had its cert parameter modified to be const in OpenSSL 4.0.

COPYRIGHT
Copyright 2015-2026 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>.