openssl_pkey_new

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

openssl_pkey_new — Generates a new private key

Description

resource openssl_pkey_new ([ array $configargs ] )

openssl_pkey_new() generates a new private and public key pair. The public component of the key can be obtained using openssl_pkey_get_public().

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

configargs: You can finetune the key generation (such as specifying the number of bits) using configargs. See openssl_csr_new() for more information about configargs.

Return Values

Returns a resource identifier for the pkey on success, or FALSE on error.

User Contributed Notes

dirt at awoms dot com

3 years ago


Working example:

$config = array(
    "digest_alg" => "sha512",
    "private_key_bits" => 4096,
    "private_key_type" => OPENSSL_KEYTYPE_RSA,
);
    
// Create the private and public key
$res = openssl_pkey_new($config);

// Extract the private key from $res to $privKey
openssl_pkey_export($res, $privKey);

// Extract the public key from $res to $pubKey
$pubKey = openssl_pkey_get_details($res);
$pubKey = $pubKey["key"];

$data = 'plaintext data goes here';

// Encrypt the data to $encrypted using the public key
openssl_public_encrypt($data, $encrypted, $pubKey);

// Decrypt the data using the private key and store the results in $decrypted
openssl_private_decrypt($encrypted, $decrypted, $privKey);

echo $decrypted;

Brad

8 years ago


It's easier than all that, if you just want the keys:

<?php
// Create the keypair
$res=openssl_pkey_new();

// Get private key
openssl_pkey_export($res, $privkey);

// Get public key
$pubkey=openssl_pkey_get_details($res);
$pubkey=$pubkey["key"];
?>

scott at brynen dot com

1 year ago


If you try and generate a new key using openssl_pkey_new(), and need to specify the size of the key, the key MUST be type-bound to integer

// works
$keysize = 1024;
$ssl = openssl_pkey_new (array('private_key_bits' => $keysize));

// fails
$keysize = "1024";
$ssl = openssl_pkey_new (array('private_key_bits' => $keysize));

// works (force to int)
$keysize = "1024";
$ssl = openssl_pkey_new (array('private_key_bits' => (int)$keysize));

jthijssen at notloxic dot nl

5 years ago


If you want to change the default private key size (1024) too something else you can use the following code:
 
<?php 
$config = array('private_key_bits' => 512);
$privKey = openssl_pkey_new($config);

?>

Mind though that the minimum number of bits is 384. Any lower will trigger an error.

NOSPAM dot alchaemist at hiperlinux dot com dot ar

11 years ago


As you probably found, getting the public key is not as direct as you might think with this documentation.

You can easily get into messages like:

Warning: openssl_pkey_get_public(): Don't know how to get public key from this private key (the documentation lied) in D:\www\keys.php on line 4

The correct steps to get the whole thing seem to be these:

<?
$dn = array("countryName" => 'XX', "stateOrProvinceName" => 'State', "localityName" => 'SomewhereCity', "organizationName" => 'MySelf', "organizationalUnitName" => 'Whatever', "commonName" => 'mySelf', "emailAddress" => 'user@domain.com');
$privkeypass = '1234';
$numberofdays = 365;

$privkey = openssl_pkey_new();
$csr = openssl_csr_new($dn, $privkey);
$sscert = openssl_csr_sign($csr, null, $privkey, $numberofdays);
openssl_x509_export($sscert, $publickey);
openssl_pkey_export($privkey, $privatekey, $privkeypass);
openssl_csr_export($csr, $csrStr);

echo $privatekey; // Will hold the exported PriKey
echo $publickey;  // Will hold the exported PubKey
echo $csrStr;     // Will hold the exported Certificate
?>

Now all you need to do is to make some research on each individual function.

zelnaga at gmail dot com

3 years ago


Getting the public key corresponding to a particular private key, through the methods provided for by OpenSSL, is a bit cumbersome. An easier way to do it is to use phpseclib, a pure PHP RSA implementation:

<?php
include('Crypt/RSA.php');

$rsa = new Crypt_RSA();
$rsa->loadKey('...');

$privatekey = $rsa->getPrivateKey();
$publickey = $rsa->getPublicKey();
?>

Doesn't require any extensions be installed.  It'll use bcmath or gmp if they're available, for speed, but doesn't even require those.