openssl_pkey_export

(PHP 4 >= 4.2.0, PHP 5, PHP 7, PHP 8)

openssl_pkey_export — Gets an exportable representation of a key into a string

Description

openssl_pkey_export(
    #[\SensitiveParameter] OpenSSLAsymmetricKey|OpenSSLCertificate|array|string $key,
    string &$output,
    #[\SensitiveParameter] ?string $passphrase = null,
    ?array $options = null
): bool

openssl_pkey_export() exports key as a PEM encoded string and stores it into output (which is passed by reference).

Note: You need to have a valid openssl.cnf installed for this function to operate correctly. See the notes under the installation section for more information.

Parameters

key
output
passphrase: The key is optionally protected by passphrase.
options: options can be used to fine-tune the export process by specifying and/or overriding options for the openssl configuration file. See openssl_csr_new() for more information about options.

Return Values

Returns true on success or false on failure.

Changelog

Version	Description
8.0.0	`key` accepts an OpenSSLAsymmetricKey or OpenSSLCertificate instance now; previously, a resource of type `OpenSSL key` or `OpenSSL X.509` was accepted.

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User Contributed Notes 6 notes

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chris dot kistner at gmail dot com ¶

13 years ago

Please take note that older versions of PHP/OpenSSL exports the RSA private key with '-----BEGIN RSA PRIVATE KEY-----' PEM tag, which includes just the privateKey field, thus omitting the version and privateKeyAlgorithm fields.

The effect of that would be that if you're converting it to DER, and then back to PEM, but using '-----BEGIN PRIVATE KEY-----' PEM tag, that the openssl_pkey_get_privatekey() function will fail!

Senthryl's code can be used to prefix the PEM encoded data with the version and privateKeyAlgorithm fields again.

The newer PHP/OpenSSL versions exports the RSA private key with '-----BEGIN PRIVATE KEY-----' PEM tag, which includes the version and privateKeyAlgorithm fields.

I noticed these differences between my two servers:
PHP Version 5.3.3 (OpenSSL 1.0.0a-fips 1 Jun 2010) on Fedora Core 12 x64
PHP Version 5.2.9 (OpenSSL 0.9.8g 19 Oct 2007) on Fedora Core 10 x64

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Senthryl ¶

14 years ago

This function can be used to create a private key for use by JCE in Java.  For example, a private key could be generated by a PHP script and the result could be used in a Java client application.



Java requires the private key in DER format with some extra ASN.1 wrapping.  The function below can be used to convert the output of openssl_pkey_export into a format suitable for input into JCE:



<?php

    function derLength($length) {

        if ($length < 128) return str_pad(dechex($length), 2, '0', STR_PAD_LEFT);

        $output = dechex($length);

        if (strlen($output) % 2 != 0) $output = '0'.$output;

        return dechex(128 + strlen($output)/2) . $output;

    }

    function convertPemToDer($pem) {

        $matches = array();

        if (!preg_match('~^-----BEGIN ([A-Z ]+)-----\s*?([A-Za-z0-9+=/\r\n]+)\s*?-----END \1-----\s*$~D', $pem, $matches)) {

            die('Invalid PEM format encountered.'."\n");

        }

        $derData = base64_decode(str_replace(array("\r", "\n"), array('', ''), $matches[2]));

        $derData = pack('H*', '020100300d06092a864886f70d010101050004'.derLength(strlen($derData))) . $derData;

                $derData = pack('H*', '30'.derLength(strlen($derData))) . $derData;

                return $derData;

    }

?>



Example use:

<?php

    $keys = openssl_pkey_new(array('digest_alg' => 'sha1', 'private_key_type' => OPENSSL_KEYTYPE_RSA, 'private_key_bits' => 2048));

    if ($keys === false) die('Failed to generate key pair.'."\n");

    if (!openssl_pkey_export($keys, $privateKey)) die('Failed to retrieve private key.'."\n");

    $javaKey = convertPemToDer($privateKey);



    file_put_contents('key_for_java.der', $javaKey);

?>



Exporting a public key for use with JCE is trickier, since the Java libraries require the key to be input as a byte array.  In effect, the public key outputted by openssl_pkey_get_details() must be base64 decoded as above, and then parsed as ASN.1 to receive the actual key bytes (this can be done either on the PHP side or the Java side).



The following link is an invaluable resource to understanding the output from these functions:

"A Layman's Guide to a Subset of ASN.1, BER, and DER"

http://luca.ntop.org/Teaching/Appunti/asn1.html

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robbat2 at gentoo dot org ¶

20 years ago

Warning, this function is NOT capable of exporting PEM-encoded public keys. It can only export private keys.

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Tk at phpRocks dot net ¶

15 years ago

Complete example to encrypt data...
=)
<pre>
<?php
// Create the keypair
$res=openssl_pkey_new();

// Get private key
openssl_pkey_export($res, $privkey, "PassPhrase number 1" );

// Get public key
$pubkey=openssl_pkey_get_details($res);
$pubkey=$pubkey["key"];
//var_dump($privkey);
//var_dump($pubkey);

// Create the keypair
$res2=openssl_pkey_new();

// Get private key
openssl_pkey_export($res2, $privkey2, "This is a passPhrase *µà" );

// Get public key
$pubkey2=openssl_pkey_get_details($res2);
$pubkey2=$pubkey2["key"];
var_dump($privkey2);
var_dump($pubkey2);

$data = "Only I know the purple fox. Trala la !";

openssl_seal($data, $sealed, $ekeys, array($pubkey, $pubkey2));

var_dump("sealed");
var_dump(base64_encode($sealed));
var_dump(base64_encode($ekeys[0]));
var_dump(base64_encode($ekeys[1]));

// decrypt the data and store it in $open
if (openssl_open($sealed, $open, $ekeys[1], openssl_pkey_get_private  ($privkey2  ,"This is a passPhrase *µà" ) ) ) {
    echo "here is the opened data: ", $open;
} else {
    echo "failed to open data";
}

?>
</pre>

Outputs :
string(963) "-----BEGIN RSA PRIVATE KEY-----
Proc-Type: 4,ENCRYPTED
DEK-Info: DES-EDE3-CBC,DA1943487C9C83B2

1/j65PJgfYqYMJSWRBk9UzXaa3USMdpkq4ztzL7IPMTPgTwVKxZbvBxzsGUXUmh6
dkWpF1jzi3B44o06mw55t2LHNkGAph/iKVP4Zvnyp/KWaZJSF+pNkvukle1u2/40
WpbNy1f8LA+ZDr7ICOCY1jy/bz/xzOCrVjqY/F4ukQik9M6bL9ZwI5fyhrcHq6EG
KsUX49XKtP/a+kQhluejzIw1aDBqmHpJTCzkL7teCk6l8x8r8mMmss1D9XqggjFm
TQncqR6IU5DClklO53JdWSFC5zTcFYMgq9lMwCQ5o4bs8iBKiE+TOFEKiggtn5zA
v189tlPtM6YePcXAm5Ymgy90Ovq3lGS4k+JkCB2Hm3HgUAB3pd9v3fOeyuFMeing
XHBuLR5nmWITzcfRuAsh0p9xe2puTVFdrLkrQFnh5Xkerm+YUQ6oTecTKRFq7S3l
hLlFIg7KbXxDjg3H5f87DCEp/isV70Rc7flvIBP6u5GX+GrmCFWjQxmGefEJQ5fZ
P7sOzHEdkOHZV7yYn+5MwQ4vDHLKQxvMqUolgvuEAzcL1o976KHAQP0accmwApXz
jry3zVqRnGvyPHo+nGwRiATJj0lAgX/j8cghJg+oo+TiXD2cM5i+Hut4dmImZNDL
3Fn2uLzklQHPlaoaz2dACyaN/sUtmVLtdnn00nuwIy2xDfHDl9MOQ6WHocU78DWo
Mw+x8B+SBsALm3Ah6JzqA8l3OAYSRxjp7YQXLQLkdCi7jEjjTl/0NVTnqU+W89XB
GBH3r8ZgIpifl3M7ZYTKLnToNL7Y/AehPs+tKgFHkXtGMKu4cIt9Ag==
-----END RSA PRIVATE KEY-----
"
string(272) "-----BEGIN PUBLIC KEY-----
MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDH82E/Dn37torKz/vhAkpji9ZS
HCyfM7JuXCbh70F75Zh2/rEVvz38yNf6f01DNXiSpzO5eTmoXD7Blsb635AOjYbl
X/WljpFbwQ2QUUDlNDAslrqXYlMzht2MCq/pjtGgk0zJx6i+HjFyV7mebeePQY/x
NOzMpmy/Ke3u+SSHRwIDAQAB
-----END PUBLIC KEY-----
"
string(6) "sealed"
string(52) "y4L3+SDVJwTfa9Em61R3X2p/LElr8N/xPCXw8kqm0co4bn3V1Tw="
string(172) "ezUo2rWLGHPv9bHE5gG8fe5qy8erGlITsSs+qGr2o8aoi98SLnyIFm4N
EQWJrmU43Ehlw72NujJ
B8chYNw2NkIDfaLChvLH54CBuCfyuF+1lWEAUwL8
FU1LftqIIt1ikjSu/8qFU6S6wikJx1pFf1IbXfOeeJVvZ1UJM2rBbudI="
string(172) "RPYLXGBXDnXDIUrFy1/GOM+//Ew/mn2syKDbhIegOJJPnpd
X6ffwXkWH5Bp8kOdz0aO9gK3whG+c
/QF+9eqcTw9SvvlrDqsP0gkRGNIOgMUiBFLoMT92JQWSI7ZesDAU0
JPRWpXsKaIOEkBGmxOMYfEd6OJWp0Mwe4COL3lP2PQ="
here is the opened data: Only I know the purple fox. Trala la !

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eric at ericseastrand dot com ¶

12 years ago

I kept banging my head against the wall today trying to figure out why the RSA keys I was generating were encrypted (they have this stuff in them)
Proc-Type: 4,ENCRYPTED
DEK-Info: DES-EDE3-CBC,BEA1180EADE1524F

I finally realized that the issue was that I was passing a password into the "openssl_pkey_export" method inadvertently.

So the moral of the story is: you have to use NULL as the password. using an empty string will still cause the key to be encrypted.

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Anonymous ¶

17 years ago

you can get 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);
fule_put_contents('./key.pub', $keyData['key']);

?>

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