如何使用 PHP 将 PEM 格式的 RSA 密钥转换为 XML 格式

Question

I'm trying to convert key pair from PEM format :

-----BEGIN PUBLIC KEY----- 

-----END PUBLIC KEY-----

Into XML format :

<RSAKeyValue>
<Exponent> </Exponent>
<Modulus> </Modulus>
</RSAKeyValue>

Is it possible using only openssl as I generate the keys through it ?

nb : my keys are stored into $privKey and $pubKey variable for test purpose, so I want to be able to $echo the XML format key and not store it into a file for the moment.

nb' : I have tried using phpseclib with an exemple found here but it gives me this error "Uncaught Error: Class "BaseController" not found in ..."

Thanks for your help

Here is the PHP code :

<?php

$config = array
(
    'config' => 'C:\xampp\htdocs\crypto\openssl.cnf',
    'default_md' => 'sha512',
    'private_key_bits' => 4096,
    'private_key_type' => OPENSSL_KEYTYPE_RSA,
);

$keypair = openssl_pkey_new($config);

openssl_pkey_export($keypair, $privKey, null, $config);

$publickey = openssl_pkey_get_details($keypair);
$pubKey = $publickey['key'];

use phpseclib3\Crypt\RSA;
echo $pubKey->toString("XML");
echo "$privKey";

?>

Answer 1

The conversion of a PEM encoded key in X.509/SPKI format to XML format can be done with phpseclib as follows:

use phpseclib3\Crypt\PublicKeyLoader;

$x509pem = '-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAunF5aDa6HCfLMMI/MZLT
5hDk304CU+ypFMFiBjowQdUMQKYHZ+fklB7GpLxCatxYJ/hZ7rjfHH3Klq20/Y1E
bYDRopyTSfkrTzPzwsX4Ur/l25CtdQldhHCTMgwf/Ev/buBNobfzdZE+Dhdv5lQw
KtjI43lDKvAi5kEet2TFwfJcJrBiRJeEcLfVgWTXGRQn7gngWKykUu5rS83eAU1x
H9FLojQfyia89/EykiOO7/3UWwd+MATZ9HLjSx2/Lf3g2jr81eifEmYDlri/OZp4
OhZu+0Bo1LXloCTe+vmIQ2YCX7EatUOuyQMt2Vwx4uV+d/A3DP6PtMGBKpF8St4i
GwIDAQAB
-----END PUBLIC KEY-----';

$publicKey = PublicKeyLoader::load($x509pem);   // import public PEM key
$xmlFormattedKey = $publicKey->toString("XML"); // export public XML key
print($xmlFormattedKey);

The output is:

<RSAKeyValue>     
    <Modulus>unF5aDa6HCfLMMI/MZLT5hDk304CU+ypFMFiBjowQdUMQKYHZ+fklB7GpLxCatxYJ/hZ7rjfHH3Klq20/Y1EbYDRopyTSfkrTzPzwsX4Ur/l25CtdQldhHCTMgwf/Ev/buBNobfzdZE+Dhdv5lQwKtjI43lDKvAi5kEet2TFwfJcJrBiRJeEcLfVgWTXGRQn7gngWKykUu5rS83eAU1xH9FLojQfyia89/EykiOO7/3UWwd+MATZ9HLjSx2/Lf3g2jr81eifEmYDlri/OZp4OhZu+0Bo1LXloCTe+vmIQ2YCX7EatUOuyQMt2Vwx4uV+d/A3DP6PtMGBKpF8St4iGw==</Modulus>
    <Exponent>AQAB</Exponent>
</RSAKeyValue>

---

For key generation OpenSSL can be used as in your code. However, the exported PEM key must be imported in the phpseclib part as shown in the code above (this import is missing in your code):

// Key generation with OpenSSL
$config = array(
    "private_key_bits" => 2048,
    "private_key_type" => OPENSSL_KEYTYPE_RSA,
);

$res = openssl_pkey_new($config);                // create key resource using $config 
//openssl_pkey_export($res, $privKey);           // export private key (PEM encoded, PKCS#8 format); not required for this example
$pubKeyDetails = openssl_pkey_get_details($res);
$x509pem = $pubKeyDetails["key"];                // export public key (PEM encoded, X.509 format)

// Key conversion with phpseclib
$publicKey = PublicKeyLoader::load($x509pem);   // import public PEM key generated with OpenSSL
$xmlFormattedKey = $publicKey->toString("XML"); // export public XML key 
print($xmlFormattedKey);

---

Alternatively, also key generation can be done with phpseclib:

use phpseclib3\Crypt\RSA;

$privateKey = RSA::createKey(2048);                              // generate private key
$xmlFormattedKey = $privateKey->getPublicKey()->toString("XML"); // export public XML key
print($xmlFormattedKey);