RSA decryption using private key - php

Question

I have a private key and encrypted string. Actually string has been encrypted using .NET modules. Now I need to decrypted the string . I tried in php but it throws me following error
openssl_private_decrypt(): key parameter is not a valid private key
I tried in perl but there it takes its own private key, But it need to use my own private key, which has been generated in our server.
Please suggest me on this issue to overcome. PHP ,Ruby , Perl Solution would be more helpful.
$crypttext="gKL/n5hkBg4jyjrLRqjQbf9gAS3xnbp1xmCmamPO33fW21JAJtlVQHYR6O1dOw3tfobMe/0uXm/kgivae9zHNey4Wt3UGzPwosUrx7V8zhC97AXya2tuENO1Fmc4Z8l9+UalwtUZxMGtl3Ua9DYuvxLP/TuavgRNpmG6eemGPag=";
$fp=fopen("private.pem","r");
$priv_key=fread($fp,8192);
fclose($fp);
openssl_private_decrypt(base64_decode($crypttext ),$newsource,false ) ;
echo "String decrypt : $newsource"**;
Private Key
<BitStrength>1024</BitStrength><RSAKeyValue><Modulus>t2G2WWIal1EinPn54ZPc3S1UgGTDxr6RFc+XEMR723VSg9toU8lSfTD7C26bUcbDxBwP1/1MbdQcx/dKX+7UlB5z79vrwfT89rUZGWeH7VZvuAawtHURgucyGMhqAZ9NxDEAl5Uo3nsNL9j1JlSBfeZf8pU5sf70KezqJTRsfrE=</Modulus><Exponent>AQAB</Exponent><P>82dZbOjQCJ7NV6EuVJXqPlh4FB65LBL1w9696sKFZuIr8refGwTZOY05se6oHbT9mn8OFXVA6A/wmz7oWNPk9w==</P><Q>wN8uixNk73DIF2SHb0aunnW5XxAIq3KxeQKoUTBAzL7BqXmKjk6XDnfxDbybmcT51wGhiO20lGg51zuxnsPXlw==</Q><DP>Kv4+VXZqCJvEOY5G2LoCPjDyRNuIabiPoKFfenARkDKzAJReji81D21am4tENrsZcIiwvCmR5WurXECoWchT0Q==</DP><DQ>qGRzW4O0VYVvfVUNFi9tF/aKwR/boe0CXDfgwvnRKbHGnfP67+JX6o73zFmGtQuQYpMO+OEpD4WsMmnw2z/7ww==</DQ><InverseQ>czq4+xiiVxb63ZtKwkxyJoDLFH0f18YlfFQTrEoAx7UE9HdjOjsJFpZ54g0yK3/S/yVgIXPwMcw6LU1QvqazPg==</InverseQ><D>Ktp/tWWSlzfToeFcvpVCMMGOFK73fTM9Tl6Di9yOoRtKnBuixqmuSCkxEVvYmgSb7PEt1qiPur6ttyEX1VFHhaugTr3aVhUpF+k7ULaHrCb8UymXXW3pp/yl/QOMPWuNKVv/GU3aQ3VTc3WUaYuOnaIkJk7uoYDQn0QqWtxtT60=</D></RSAKeyValue>

Answer 1

phpseclib, a pure PHP RSA implementation, supports XML private keys in this format. Usage example:
<?php
include('Crypt/RSA.php');
$rsa = new Crypt_RSA();
$rsa->loadKey('...'); // private key
echo $rsa->decrypt($ciphertext);
?>

Answer 2

you need to convert the key and actually use it:
$crypttext="gKL/n5hkBg4jyjrLRqjQbf9gAS3xnbp1xmCmamPO33fW21JAJtlVQHYR6O1dOw3tfobMe/0uXm/kgivae9zHNey4Wt3UGzPwosUrx7V8zhC97AXya2tuENO1Fmc4Z8l9+UalwtUZxMGtl3Ua9DYuvxLP/TuavgRNpmG6eemGPag=";
$priv_key = openssl_pkey_get_private("file://path/to/private.pem");
openssl_private_decrypt(base64_decode($crypttext ), $newsource, $priv_key ) ;
echo "String decrypt : $newsource"**;

Answer 3

A solution is to generate a key in the format PHP expects (.pem file, I think the format is called DER ASN.1 but I'm not sure), using openssl (under linux usually), and then convert it, still using OpenSSL, to a format that .NET can read. See this SO answer for more details.
Under Linux:
openssl genrsa -out private.pem 1024
openssl rsa -in private.pem -out public.pem -pubout
openssl req -nodes -x509 -days 3650 -subj '/CN=www.example.com/emailAddress=info#example.com' -new -key private.pem -out certificate.crt
openssl pkcs12 -export -out certificate.pfx -inkey private.pem -in certificate.crt
Under .NET:
// Get the public key
X509Certificate2 pubCertificate = new X509Certificate2("certificate.crt", "passphrase", X509Certificates.X509KeyStorageFlags.Exportable);
RSACryptoServiceProvider public = (RSACryptoServiceProvider)(pubCertificate.PublicKey.Key);
System.Console.WriteLine(public.ToXmlString(false));
// Get the private key
X509Certificate2 privCertificate = new X509Certificate2("certificate.pfx", "passphrase", X509Certificates.X509KeyStorageFlags.Exportable);
RSACryptoServiceProvider private = (RSACryptoServiceProvider)(privCertificate .PrivateKey);
System.Console.WriteLine(private.ToXmlString(true));