CascadiaPHP 2024


(PHP 4 >= 4.0.6, PHP 5, PHP 7, PHP 8)

openssl_x509_checkpurposeVerifies if a certificate can be used for a particular purpose


    OpenSSLCertificate|string $certificate,
    int $purpose,
    array $ca_info = [],
    ?string $untrusted_certificates_file = null
): bool|int

openssl_x509_checkpurpose() examines a certificate to see if it can be used for the specified purpose.



The examined certificate.


openssl_x509_checkpurpose() purposes
Constant Description
X509_PURPOSE_SSL_CLIENT Can the certificate be used for the client side of an SSL connection?
X509_PURPOSE_SSL_SERVER Can the certificate be used for the server side of an SSL connection?
X509_PURPOSE_NS_SSL_SERVER Can the cert be used for Netscape SSL server?
X509_PURPOSE_SMIME_SIGN Can the cert be used to sign S/MIME email?
X509_PURPOSE_SMIME_ENCRYPT Can the cert be used to encrypt S/MIME email?
X509_PURPOSE_CRL_SIGN Can the cert be used to sign a certificate revocation list (CRL)?
X509_PURPOSE_ANY Can the cert be used for Any/All purposes?
These options are not bitfields - you may specify one only!


ca_info should be an array of trusted CA files/dirs as described in Certificate Verification.


If specified, this should be the name of a PEM encoded file holding certificates that can be used to help verify the certificate, although no trust is placed in the certificates that come from that file.

Return Values

Returns true if the certificate can be used for the intended purpose, false if it cannot, or -1 on error.


Version Description
8.0.0 certificate accepts an OpenSSLCertificate instance now; previously, a resource of type OpenSSL X.509 was accepted.
8.0.0 untrusted_certificates_file is nullable now.
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User Contributed Notes 3 notes

dingyuan at tencent dot com
3 years ago
in one word :if you set $purpose=0, you can use this function to verify certificate chain.


I want to verify a certificate chain. just like this:
userCert.pem => middleCert.pem => rootCert.pem

I figured that none of these openssl functions provide this function directly. And some friends have same need as me, "mikey at badpenguins dot com" even write his own code to verify certificate chain(you can see notes below openssl_verify).

and I notice a note which has '-3' likes below openssl_verify, it says "validating an X509 certificate chain in php seems to be possible with openssl_x509_checkpurpose()", and I read the source code about this function, the given constant var about $purpose (like X509_PURPOSE_SSL_CLIENT ) is 1-7, and if you set $purpose among 1-7, you cannot verify the cert chain. Set $purpose=0 can get the truly result about verify a cert chain.

and I give that '-3' note a thumb-up, now it has -2 , lol.
adr at NOSPAM dot entropymatrix dot com
11 years ago
The following is an example usage of openssl_x509_checkpurpose. It is equivalent to the openssl verify command as follows:
openssl verify -CApath $openssl_cadir -purpose sslserver $openssl_crtfile


$x509_res = openssl_x509_read(file_get_contents($openssl_crtfile));
$x509_res)) {
'x509 cert could not be read'."\n";
$valid = openssl_x509_checkpurpose($x509_res,X509_PURPOSE_SSL_SERVER,array($openssl_cadir));
if (
$valid === true) {
'Certificate is valid for use as SSL server'."\n";
} else {
'Certificate validation returned'.$valid."\n";
chaoszcat at gmail dot com
11 years ago
Few days ago I dual boot my system into Windows 8 and play around with it, and then I boot it back to windows 7, and all of sudden this function fails by returning me 0 all the time.

Spent almost two hours digging google for no result, I almost end my research.

Then (I don't know why) I did a system time update (synchronize with, and all of sudden, this function returns me 1 (true).

It's true that when I boot back to Windows 7 my time has been screwed by a few hours later than my current time, and I did a manual change on it. I doubt this has anything to do with this function?

Hope it helps.

Keywords: google discovery, openid, discovery
Platform: Windows 7 64bit, PHP 5.3.13
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