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

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

Chilkat Perl Downloads Perl Module for Windows, MacOS, Linux, Alpine Linux, Solaris

use chilkat();

# 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=";

$crypt = chilkat::CkCrypt2->new();

$crypt->put_CryptAlgorithm("aes");
$crypt->put_CipherMode("gcm");
$crypt->put_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..
$bdEncrypted = chilkat::CkBinData->new();
$bdAuthTag = chilkat::CkBinData->new();
$success = $bdEncrypted->AppendEncoded($cipherBase64Url,"base64url");

$numBytes = $bdEncrypted->get_NumBytes();
$authTagHex = $bdEncrypted->getEncodedChunk($numBytes - 16,16,"hex");

print "Auth tag in hex: " . $authTagHex . "\r\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->put_EncodingMode("base64");
$originalText = $crypt->decryptStringENC($bdEncrypted->getEncoded("base64"));
if ($crypt->get_LastMethodSuccess() == 0) {
    print $crypt->lastErrorText() . "\r\n";
}
else {
    print $originalText . "\r\n";
    print "Success." . "\r\n";
}

# Decrypted text