(PHP 4 >= 4.2.0, PHP 5, PHP 7)
openssl_pkey_get_public — Extract public key from certificate and prepare it for use
openssl_get_publickey() extracts the public key from
certificate and prepares it for use by other
functions.
certificate
certificate can be one of the following:
Returns a positive key resource identifier on success, or FALSE on error.
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);
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']);
?>
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
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.
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); ?>
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.
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']);
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.
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-----";
