openssl_pkey_get_public

(PHP 4 >= 4.2.0, PHP 5, PHP 7)

openssl_pkey_get_public — Extract public key from certificate and prepare it for use

说明

resource openssl_pkey_get_public ( mixed $certificate )

openssl_get_publickey() extracts the public key from certificate and prepares it for use by other functions.

参数

certificate

certificate can be one of the following:

  1. an X.509 certificate resource
  2. a string having the format file://path/to/file.pem. The named file must contain a PEM encoded certificate/public key (it may contain both).
  3. A PEM formatted public key.

返回值

Returns a positive key resource identifier on success, or FALSE on error.

User Contributed Notes

Joey 13-Sep-2016 12:24
I spent a few hours raging with this function and hitting my head on the desk trying to get it to load a public PEM key.

This function can leave errors in openssl_error_string even if it succeeded so this can cause a lot of confusion further down. Especially if you're prototyping and haven't put full checks on return values in yet. The error will not be cleared either when calling other functions successfully.

To avoid confusion, you should always check the return result and only call openssl_error_string after calling an openssl function that returned failure (false).
Rurri 26-Feb-2012 04:35
If you have a 4096 bit key pair and are trying to use a public key that begins with:

-----BEGIN RSA PUBLIC KEY-----
 
and you need to convert it for this function to use, you can convert it by prepending the static header information:

MIICIjANBgkqhkiG9w0BAQEFAAOCAg8A

Such as:

$start_key = str_replace('-----BEGIN RSA PUBLIC KEY-----', '', $start_key);
$start_key = trim(str_replace('-----END RSA PUBLIC KEY-----', '', $start_key));
$key = 'MIICIjANBgkqhkiG9w0BAQEFAAOCAg8A' . str_replace("\n", '', $start_key);
$key = "-----BEGIN PUBLIC KEY-----\n" . wordwrap($key, 64, "\n", true) . "\n-----END PUBLIC KEY-----";
ppostma1 15-Jun-2011 05:32
found the cert/public key for 2048 bits is this format:

-----BEGIN PUBLIC KEY-----
X509 signature + PEM sig + modulus + 'ID' + exponent
-----END PUBLIC KEY-----

so the variables are:
-----BEGIN PUBLIC KEY-----
'MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8A' . 'MIIBCgKCAQEA' . $modulus . 'ID' . $exponent
-----END PUBLIC KEY-----

<?php wordwrap($cert, 64, "\r\n", true); ?>
info at steyla dot com 21-Dec-2010 08:55
If you are trying to read a PKCS#1 RSA public key you run into trouble, because openssl wants the public key in X.509 style.

The PKCS#1 RSA public key

-----BEGIN RSA PUBLIC KEY-----
MIIBCgKCAQEAgYxTW5Yj+5QiQtlPMnS9kqQ/HVp+T2KtmvShe68cm8luR7Dampmb
[...]
cbn6n2FsV91BlEnrAKq65PGJxcwcH5+aJwIDAQAB
-----END RSA PUBLIC KEY-----

.. is  not readable while the X.509 style public key

-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAgYxTW5Yj+5QiQtlPMnS9
[..]
JwIDAQAB
-----END PUBLIC KEY-----

is. You can use an easy (and dirty) work around to read the PKCS#1 RSA anyway. The first few bytes of the X.509 style public key contain header information and can shamelessly be copied.

In other words: Delete everything after the first 32 bytes from the above X.509 key (starting behind Q8A) and attach your PKCS#1 data, reformat to 64 bytes length and use it with openssl.

Please note: The above example only works for 2048 bit length.

Like I said - it's kind of dirty - but hey - if you're as desperate as I was.

Michaela
Paul Clark 15-Feb-2010 04:50
Note this will read public keys from PEM formatted public keys as well:

<?php
$key = <<<EOF
-----BEGIN PUBLIC KEY-----
MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDXX/MsKEBLcLeKA1d/i7ufG1qs
qS97xFkIRSeX3TwmHic843AfVrzoh2pZUeOvK9ZLZQpHSM7DoHMYDGD1273+FvZX
Ypf5LiFtecfxko/Cku16zy6WAeCYVFjjlveBhwPmPCIk+qDRYeiIW05QE2XK+CuD
nJ7sxxXIJSSgD3Jo5wIDAQAB
-----END PUBLIC KEY-----
EOF;

print $key;
$res = openssl_pkey_get_public($key);
print_r(openssl_pkey_get_details($res));
?>

Note that contrary to the documentation, openssl_pkey_get_details() will *not* read PEM directly, and you have to go through this step.
thelen dot shar at gmail dot com 25-Jan-2009 09:08
Found it difficult to get my head around this due to lack of documentation.

But the process I followed for all this was:
Generate private key:
openssl genrsa -des3 -out private.pem 1024

Generate public key:
openssl rsa -in private.pem -out public.pem -outform PEM -pubout

Then in PHP:
$passphrase = 'somestring';
$key_private = openssl_get_privatekey(file_get_contents('private.pem'), $passphrase);
$key_public = openssl_get_publickey(file_get_contents('public.pem'));

Probably not the best way of doing it, but a lot simpler than the other examples on the site. I was having trouble getting the pubkey, it wasn't exactly specified very well, and I had made a mistake in generating it so it wasn't working for that reason as well.
VaD 06-Jun-2008 07:36
Small error in this code:

$pub_key = openssl_pkey_get_public(file_get_contents('./cert.crt'));
$keyData = openssl_pkey_get_details($pub_key);
file_put_contents('./key.pub', $keyData['key']);
07-May-2007 09:40
you can get (and save to file) public key using openssl_pkey_get_details(resource $key ) function:

<?php
$pub_key = openssl_pkey_get_public(file_get_contents('./cert.crt'));
$keyData = openssl_pkey_get_details($pub_key);
file_put_contents('./key.pub', $keyData['key']);
?>
dankybastard at hotmail 09-Feb-2005 05:52
You must also use the string representation of the certificate to get the public key resource:

$dn = array();  // use defaults
$res_privkey = openssl_pkey_new();
$res_csr = openssl_csr_new($dn, $res_privkey);
$res_cert = openssl_csr_sign($res_csr, null, $res_privkey, $ndays);

openssl_x509_export($res_cert, $str_cert);

$res_pubkey = openssl_pkey_get_public($str_cert);
09-Aug-2004 08:44
This documentation notes it can take a PEM-formatted private key, but as per bug #25614, this is not possible in any form. The function simply returns a FALSE.

The only thing you can get public keys out of are X.509 certificates.

Furthermore, there is NO way to export a public key into a PEM-encoded form.