(PHP Extension) Decrypt a SAML Response

Demonstrates how to decrypt a SAML response.

Note: This example requires Chilkat v9.5.0.76 or greater.

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<?php

// The version number (9_5_0) should match version of the Chilkat extension used, omitting the micro-version number.
// For example, if using Chilkat v9.5.0.48, then include as shown here:
include("chilkat_9_5_0.php");

//  This example requires the Chilkat API to have been previously unlocked.
//  See Global Unlock Sample for sample code.

//  This example decrypts this SAML response:

//  <?xml version="1.0" encoding="UTF-8" ?>
//  <saml2p:Response Destination="https://deskflow-asp2.com/ubc/ubcdfe.dll/cwlacs" ID="_e4585eaeedbcaf7c24dff7f1ee2499f5" IssueInstant="2018-10-11T17:46:20.727Z" Version="2.0" xmlns:saml2p="urn:oasis:names:tc:SAML:2.0:protocol">
//      <saml2:Issuer xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion">https://authentication.stg.id.ubc.ca</saml2:Issuer>
//      <ds:Signature xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
//          <ds:SignedInfo>
//              <ds:CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/>
//              <ds:SignatureMethod Algorithm="http://www.w3.org/2001/04/xmldsig-more#rsa-sha256"/>
//              <ds:Reference URI="#_e4585eaeedbcaf7c24dff7f1ee2499f5">
//                  <ds:Transforms>
//                      <ds:Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature"/>
//                      <ds:Transform Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/>
//                  </ds:Transforms>
//                  <ds:DigestMethod Algorithm="http://www.w3.org/2001/04/xmlenc#sha256"/>
//                  <ds:DigestValue>1ui22tqFyYEOoWI19CMwz4n+ynxNjLDGdTeRMdi60EU=</ds:DigestValue>
//              </ds:Reference>
//          </ds:SignedInfo>
//          <ds:SignatureValue>ROg7FXV6vsp8socVhdo76/i7cRHGGKIveAiScKdujZT0QrHVqIvvbZ/RnwvEMJ9H9i/kJFAQA171
//  		Eo2kDjSdvNFQ/YcKaJUwMtAwT05yVatGV42RZKEf7ME+vpcCTR1LWZdrhat1FWCg1MNQwNWB0EL5
//  		fEP2a4jAcSTB8tFbjTAHsv7IWC39E5RVv99mACYXLa7iGZLtORANZxgYu5qQgmH6pUkI6Z1cpmf+
//  		m9mIjKM6LF0EvLfWOBWL6udZ+GsHPOLjVTJg+1S0xb9FQCYDVW1QhbjSS0icKHKTNNbrsaxllVDY
//  		m4q27YQjRh+XxugPgvsZ61Pxlto8Jbg+6jUlMQ==</ds:SignatureValue>
//          <ds:KeyInfo>
//              <ds:X509Data>
//                  <ds:X509Certificate>MIIDTTCCAjWgAwIBAgIVAJccYyIV6wly8XyddumpgnHMJ2JLMA0GCSqGSIb3DQEBCwUAMCcxJTAj
//  			BgNVBAMMHGF1dGhlbnRpY2F0aW9uLnN0Zy5pZC51YmMuY2EwHhcNMTcwMzAxMTk1NDM0WhcNMzcw
//  			...
//  			xUuh6HuHKIwQqHBz7udxbH3Zbb6jXGDJjiDHt1LRJ8xbVisFIcDlIwsGQQi0HeEJfx4P</ds:X509Certificate>
//              </ds:X509Data>
//          </ds:KeyInfo>
//      </ds:Signature>
//      <saml2p:Status>
//          <saml2p:StatusCode Value="urn:oasis:names:tc:SAML:2.0:status:Success"/>
//      </saml2p:Status>
//      <saml2:EncryptedAssertion xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion">
//          <xenc:EncryptedData Id="_314d80b9cf02d8eda8d686a6ffd626cf" Type="http://www.w3.org/2001/04/xmlenc#Element" xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">
//              <xenc:EncryptionMethod Algorithm="http://www.w3.org/2001/04/xmlenc#aes128-cbc" xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"/>
//              <ds:KeyInfo xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
//                  <xenc:EncryptedKey Id="_d7b6da6fb59a627ebb4a96928441ab79" Recipient="https://ubcdfe.deskflow-asp2.com" xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">
//                      <xenc:EncryptionMethod Algorithm="http://www.w3.org/2001/04/xmlenc#rsa-oaep-mgf1p" xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">
//                          <ds:DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1" xmlns:ds="http://www.w3.org/2000/09/xmldsig#"/>
//                      </xenc:EncryptionMethod>
//                      <ds:KeyInfo>
//                          <ds:X509Data>
//                              <ds:X509Certificate>MIICuzCCAiQCCQD3bpigRnKMSzANBgkqhkiG9w0BAQsFADCBoTELMAkGA1UEBhMCQ0ExEDAOBgNV
//  				BAgMB09udGFyaW8xEDAOBgNVBAcMB1Rvcm9udG8xJjAkBgNVBAoMHVRhY3RpY2FsIEJ1c2luZXNz
//  				...
//  				kVRcHd1UK3q7G8FoykWjdQz/0EoMTfEZ+Md56mLOe48eMUZV2ONZuL1kDCEKw1UwkaDQI4Pf8pzx
//  				82b9rgw9wBDtvu5eFPlUGEGIBw==</ds:X509Certificate>
//                          </ds:X509Data>
//                      </ds:KeyInfo>
//                      <xenc:CipherData xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">
//                          <xenc:CipherValue>BNHfUOpgdPE5BgpN2VIZIDthMAv1rxk91qVnWyCZOG9bmUKChJtTUqMpndot7VJwYuyKFshkAdnT
//  				D79KGdlSA1xHKcVeZXXzDWglqSyYjzhDCsyOhPaI4HelMFgCLwyFz89uEpUpqlvfl8ol3Am/XnzQ
//  				Vp7V7oS76hocjUI51Qs=</xenc:CipherValue>
//                      </xenc:CipherData>
//                  </xenc:EncryptedKey>
//              </ds:KeyInfo>
//              <xenc:CipherData xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">
//                  <xenc:CipherValue>R6l7tmbnXrOfBgB8lA3KnwLYsLH5ZO5omQ7Hp5K05atzw2o55xmCXVMYhNneFxMtxUh6raEyHeZX
//  			PTZNgWrvdqc4GYND/R7MhRrJzk9OAq1WyoOXwbtRpwNDwWA4N2IuprPQJbvjVxaw/PesZMZwZqlp
//  			...
//  			zm9zAxahyu8Ooe8M4r3HN2cY0JxxxkZtDiulbnyA+rRtXfBRJtangvFQ4iFAnzM/Yg9hMyW9jcu0
//  			S7FzuRB9ONMxi+nh0IFWgqp+</xenc:CipherValue>
//              </xenc:CipherData>
//          </xenc:EncryptedData>
//      </saml2:EncryptedAssertion>
//  </saml2p:Response>

//  The sample encrypted SAML response and RSA private key are available online:
$http = new CkHttp();
$sbSamlResponse = new CkStringBuilder();
$sbPrivateKeyPem = new CkStringBuilder();
$success = $http->QuickGetSb('https://chilkatdownload.com/data/samlresponse.xml',$sbSamlResponse);
if ($success == true) {
    $success = $http->QuickGetSb('https://chilkatdownload.com/data/samlresponse_privkey.pem',$sbPrivateKeyPem);
}

if ($success != true) {
    print $http->lastErrorText() . "\n";
    exit;
}

$xml = new CkXml();
$xml->LoadSb($sbSamlResponse,true);

//  Load the RSA private key..
$privkey = new CkPrivateKey();
$success = $privkey->LoadPem($sbPrivateKeyPem->getAsString());
if ($success != true) {
    print $privkey->lastErrorText() . "\n";
    exit;
}

//  Prepare an RSA object w/ the private key...
$rsa = new CkRsa();
$success = $rsa->ImportPrivateKeyObj($privkey);
if ($success != true) {
    print $rsa->lastErrorText() . "\n";
    exit;
}

//  RSA will be used to decrypt the xenc:EncryptedKey
//  The bytes to be decrypted are in xenc:CipherValue (in base64 format)
$encryptedAesKey = $xml->getChildContent('saml2:EncryptedAssertion|xenc:EncryptedData|ds:KeyInfo|xenc:EncryptedKey|xenc:CipherData|xenc:CipherValue');
if ($xml->get_LastMethodSuccess() != true) {
    print 'Encrypted AES key not found.' . "\n";
    exit;
}

print 'Encrypted AES key (base64) = ' . $encryptedAesKey . "\n";

$bdAesKey = new CkBinData();
$bdAesKey->AppendEncoded($encryptedAesKey,'base64');

$sbRsaAlg = new CkStringBuilder();
$sbRsaAlg->Append($xml->chilkatPath('saml2:EncryptedAssertion|xenc:EncryptedData|ds:KeyInfo|xenc:EncryptedKey|xenc:EncryptionMethod|(Algorithm)'));
print 'sbRsaAlg contains: ' . $sbRsaAlg->getAsString() . "\n";
if ($sbRsaAlg->Contains('rsa-oaep',true) == true) {
    $rsa->put_OaepPadding(true);
}

//  Note: The DecryptBd method is introduced in Chilkat v9.5.0.76
$success = $rsa->DecryptBd($bdAesKey,true);
if ($success != true) {
    print $rsa->lastErrorText() . "\n";
    exit;
}

print 'Decrypted AES key (hex) = ' . $bdAesKey->getEncoded('hex') . "\n";

//  Get the encrypted XML (in base64) to be decrypted w/ the AES key.
$encrypted64 = $xml->getChildContent('saml2:EncryptedAssertion|xenc:EncryptedData|xenc:CipherData|xenc:CipherValue');
if ($xml->get_LastMethodSuccess() != true) {
    print 'Encrypted data not found.' . "\n";
    exit;
}

$bdEncrypted = new CkBinData();
$bdEncrypted->AppendEncoded($encrypted64,'base64');

//  Get the symmetric algorithm:  "http://www.w3.org/2001/04/xmlenc#aes128-cbc"
//  and set the symmetric decrypt properties.
$crypt = new CkCrypt2();
$sbAlg = new CkStringBuilder();
$sbAlg->Append($xml->chilkatPath('saml2:EncryptedAssertion|xenc:EncryptedData|xenc:EncryptionMethod|(Algorithm)'));
if ($sbAlg->Contains('aes128-cbc',true) == true) {
    $crypt->put_CryptAlgorithm('aes');
    $crypt->put_KeyLength(128);
    $crypt->put_CipherMode('cbc');
    //  The 1st 16 bytes of the encrypted data are the AES IV.
    $crypt->SetEncodedIV($bdEncrypted->getEncodedChunk(0,16,'hex'),'hex');
    $bdEncrypted->RemoveChunk(0,16);
}

//  Other algorithms, key lengths, etc, can be supported by checking for different Algorithm attribute values..

$crypt->SetEncodedKey($bdAesKey->getEncoded('hex'),'hex');

//  AES decrypt...
$success = $crypt->DecryptBd($bdEncrypted);
if ($success != true) {
    print $crypt->lastErrorText() . "\n";
    exit;
}

//  Get the decrypted XML
$decryptedXml = $bdEncrypted->getString('utf-8');
print 'Decrypted XML:' . "\n";
print $decryptedXml . "\n";

//  The decrypted XML looks like this:

//  <saml2:Assertion xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion" ID="_226e565c548db7986d165d7d969b48b4" IssueInstant="2018-10-11T17:46:20.727Z" Version="2.0">
//  ...
//  ...
//  ...
//  </saml2:Assertion>

$xmlAssertion = new CkXml();
$xmlAssertion->LoadXml($decryptedXml);

//  Replace the saml2:EncryptedAssertion XML subtree with the saml2:Assertion XML.
// xmlEncryptedAssertion is a CkXml
$xmlEncryptedAssertion = $xml->FindChild('saml2:EncryptedAssertion');
$xmlEncryptedAssertion->SwapTree($xmlAssertion);

//  The decrypted XML assertion has now replaced the encrypted XML assertion.
//  Examine the fully decrypted XML document:
print 'Full XML SAML document with decrypted assertion:' . "\n";
print $xml->getXml() . "\n";

?>