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PHP - Function openssl_pkey_export_to_file()


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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 −

-----BEGIN PRIVATE KEY-----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-----END PRIVATE KEY-----

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 −

-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAnbGAblUCP6sZvbi2JM4G
PcLmKK9flGQq6EE+yvMWrEUnIPGOLJUEB06dE8inIMQTYDmdmjn7HgUAlIDaViw+
aSv3XBZJqBTm7xtW4488oKuCzdBuJbnomtGttFWOk4cjb8kG+Kza6v0AB+P0eUru
cPkwnJF4F1pGY1pszSMsL3/s7OcIzjiKUKu5vHJxUWO7baVovq+gv9+O24Pd0GhB
t6RC/pgK/42YqZ2YW5V+JiuCFFkTVPusviunAOLLpDwoyPIROvXdML2TKopiowOd
nmOkNRrW81duRF8Z4dcn7jnf2sKExpLBgAtcV05OufZIv3VeeTD0ISbCJhn0zmx/
SQIDAQAB
-----END PUBLIC KEY-----
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