PHP - Function openssl_pkey_export_to_file()

Definition and Usage

The openssl_pkey_export_to_file() function will export the key to a file.

Description

The openssl_pkey_export_to_file() function saves the key in a PEM format.PEM stands for Privacy-Enhanced Mail and it mainly stores cryptographic keys and certificates.

Syntax

openssl_pkey_export_to_file ( mixed $key , string $outfilename [, string $passphrase [, array $configargs ]] ) : bool

Parameters

Sr.No	Parameter	Description
1	key	The key you want to export to file.
2	outfilename	The outfilename is the path where you want to save the .pem file.
3	passphrase	The password you can use to protect the file.
4	configargs	The parameter configargs is the configuration details that needs to be given to the function to generate the private/public key pair.The details are described below.

configargs

By default openssl_pkey_new() makes use of configuration details present in openssl.cnf. But using configargs you can overwrite them.The config details are as follows:

key in configargs	type	key used in openssl.conf	description
digest_alg	string	default_md	Digest methods that you get from openssl_get_md_methods().
x509_extensions	string	x509_extensions	Extensions used when creating an x509 certificate.
req_extensions	string	req_extensions	Extensions used when creating a CSR.
private_key_bits	integer	default_bits	Specifies how many bits to be used while generating a private key.
private_key_type	integer	none	The type of private key to create. It can be one of OPENSSL_KEYTYPE_DSA, OPENSSL_KEYTYPE_DH, OPENSSL_KEYTYPE_RSA or OPENSSL_KEYTYPE_EC. The default value is OPENSSL_KEYTYPE_RSA.
encrypt_key	boolean	encrypt_key	Whether the exported key be encrypted?
encrypt_key_cipher	integer	none	Cipher constants like OPENSSL_CIPHER_RC2_40 (integer),OPENSSL_CIPHER_RC2_128 (integer),OPENSSL_CIPHER_RC2_64 (integer),OPENSSL_CIPHER_DES (integer), OPENSSL_CIPHER_3DES (integer) etc.
curve_name	string	none	One of the curve name returned by this function openssl_get_curve_names().
config	string	N/A	You can change the configuration in openssl.conf as per your requirement and give the path of it here.

Return Values

PHP openssl_pkey_export_to_file() function returns true if there is success and false if failure.

PHP Version

This function will work from PHP Version greater than 5.0.0.

Example 1

Working of openssl_pkey_export_to_file() −

<?php
   //creating private key
   $privkey = openssl_pkey_new();
   openssl_pkey_export_to_file($privkey, 'C:/xampp/htdocs/modules/openssl/keytest.pem');
?>

The details stored in file keytest.pem is as follows −

Example 2

To fetch the key from .pem file −

<?php
   //creating private key
   $privkey = openssl_pkey_new();
   openssl_pkey_export_to_file($privkey, 'C:/xampp/htdocs/modules/openssl/keytest.pem');
	
   //using .pem file with private key.
   $testprivatekey = openssl_get_privatekey(file_get_contents('C:/xampp/htdocs/modules/openssl/keytest.pem'));
   if ($testprivatekey === false) {
      var_dump(openssl_error_string());
   } else {
      //var_dump($testprivatekey);
      $key_details = openssl_pkey_get_details($testprivatekey);
      print_r($key_details["key"]);	
   }
?>

The details stored in file test-csr1.pem is as follows −

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