(PHP ActiveX) Decrypt 256-bit AES GCM Produced by Something Unknown

Demonstrates how to decrypt something produced elsewhere (unknown) with 256-bit AES GCM.

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows Note: The php_com_dotnet.dll may need to be enabled inside of php.ini.

<?php

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

// We have the following to decrypt:

// Key (Base64): 
$keyBase64 = 'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx';

// IV (Base64Url):
$ivBase64Url = 'xrvaINMLqotAbWRK';

// ciphertext (base64url):
$cipherBase64Url = 'RtGNAS-zQOxSB8W0HfqJjCoyt9KgImW_l-HjVC40hOOl-RNfRF3hzDIT1kvFVF8i_KX9XmqAftb6lyq-jLCEc_MSgqt3q1ixv3Ez4SbS3G5e3qGzLwxIMi2sCt00aDNwK2ipsJ4aw8s7ePPnl4oY-y1st9rwCWR0rrgEZwS9jmS4uJWGPn9K3jbKRnMslznDbtFLNJctMVXBTP-cv47JelxLCBOQSlK29rMuEFrhHR_VQrPq6gtZaBVSXZSYT0XOklp7nu9mVhrMCRtBCC5oiu5MPE5JYx4ANo3hUY7_NyQl2bpn9GfRXrdvqRGE-gy2upj-cDkm0t_tV8xmYge9DBQTH3B_4BGl2qTk_o-m7pEmKkS8XSdQhGcuFlykqrkE8SzB5I8esfzWOM0pwxbz0H_VaylKYHY=';

// For versions of Chilkat < 10.0.0, use new COM('Chilkat_9_5_0.Chilkat.Crypt2')
$crypt = new COM("Chilkat.Crypt2");

$crypt->CryptAlgorithm = 'aes';
$crypt->CipherMode = 'gcm';
$crypt->KeyLength = 256;

$success = $crypt->SetEncodedAad('random','ascii');
$crypt->SetEncodedKey($keyBase64,'base64');
$crypt->SetEncodedIV($ivBase64Url,'base64url');

// The cipher text contains the 16-byte auth tag at the end.
// get it separately..
// For versions of Chilkat < 10.0.0, use new COM('Chilkat_9_5_0.Chilkat.BinData')
$bdEncrypted = new COM("Chilkat.BinData");
// For versions of Chilkat < 10.0.0, use new COM('Chilkat_9_5_0.Chilkat.BinData')
$bdAuthTag = new COM("Chilkat.BinData");
$success = $bdEncrypted->AppendEncoded($cipherBase64Url,'base64url');

$numBytes = $bdEncrypted->NumBytes;
$authTagHex = $bdEncrypted->getEncodedChunk($numBytes - 16,16,'hex');

print 'Auth tag in hex: ' . $authTagHex . "\n";

$success = $bdAuthTag->AppendEncoded($authTagHex,'hex');
$bdEncrypted->RemoveChunk($numBytes - 16,16);

// Use this special value to tell Chilkat to ignore the auth tag.
$success = $crypt->SetEncodedAuthTag('FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF','hex');

// Decrypt
$crypt->EncodingMode = 'base64';
$originalText = $crypt->decryptStringENC($bdEncrypted->getEncoded('base64'));
if ($crypt->LastMethodSuccess == 0) {
    print $crypt->LastErrorText . "\n";
}
else {
    print $originalText . "\n";
    print 'Success.' . "\n";
}

// Decrypted text

?>