How to decrypt the content of a DLC container file via Powershell?

Question

How can I decode the body of a jdownloader *.DLC container file with Powershell?

Answer 1

I have managed to write a small Powershell snippet to decrypt a DLC container file based on the PyLoad code reference.

It prompts for a given file, decrypts the content and puts the URLs into the clipboard. For the archives here the working sample code:

# script for decoding a DLC-file:

Remove-Variable * -ea 0
$ErrorActionPreference = 'stop'
$utf8 = [System.Text.Encoding]::UTF8

# file selector:
Add-Type -AssemblyName 'System.Windows.Forms'
$browser = [System.Windows.Forms.OpenFileDialog]::new()
$browser.Filter = 'DLC files (*.dlc)|*.dlc'
$browser.InitialDirectory = "$env:USERPROFILE\Downloads"
$null = $browser.ShowDialog()
$fileName = $browser.FileName
if (![System.IO.File]::Exists($fileName)) {break}

$dlc = [System.IO.File]::ReadAllText($fileName)
$len = $dlc.Length
$key = $dlc.Substring($len-88)
$data  = $dlc.Substring(0,$len-88)
$bytes = [System.Convert]::FromBase64String($data)

$aesKey = 'cb99b5cbc24db398'
$aesIV  = '9bc24cb995cb8db3'
$url    = "http://service.jdownloader.org/dlcrypt/service.php?srcType=dlc&destType=pylo&data=$key"

$result = Invoke-WebRequest $url
$rc64 = ([xml]$result.Content).rc
$rc   = [System.Convert]::FromBase64String($rc64)

$aes = [System.Security.Cryptography.Aes]::Create()
$aes.Key = $utf8.GetBytes($aeskey)
$aes.IV  = $utf8.GetBytes($aesIV)
$aes.Padding = [System.Security.Cryptography.PaddingMode]::None
$dec = $aes.CreateDecryptor()
$result = $dec.TransformFinalBlock($rc, 0, $rc.Length)
$dec.Dispose()

$aes.key = $result
$aes.IV  = $result
$dec = $aes.CreateDecryptor()
$enc = $dec.TransformFinalBlock($bytes, 0, $bytes.Length)
$dec.Dispose()

$b64  = $utf8.GetString($enc).Trim([char]0)
$byte = [System.Convert]::FromBase64String($b64)
$xml  = [xml]$utf8.GetString($byte)
$urlList = foreach($url64 in $xml.dlc.content.package.file.url) {
    $urlb = [System.Convert]::FromBase64String($url64)
    $utf8.GetString($urlb)
}

cls
$urlList | Set-Clipboard
$urlList

Here is also a short demo how to encode any text into a DLC-format:

# DLC-encryption:

# get a random encryption key (RCP):
$bytes = [System.Security.Cryptography.Rfc2898DeriveBytes]::new($null,8)
$hexbin = [System.Runtime.Remoting.Metadata.W3cXsd2001.SoapHexBinary]::new($bytes.Salt)
$rcp = $hexbin.ToString().ToLower()

# let jdownloader generate an RC-value for this key:
$url    = "http://service.jdownloader.org/dlcrypt/service.php?jd=1&srcType=plain&data=$rcp"
$result = Invoke-WebRequest $url
$rc = ([xml]"<xml>$($result.Content)</xml>").xml.rc
# if we store the rcp/rc-pair, then we could decode a DLC in offline mode

# encode any information with our initial key:
$data = 'something to encode'
$bytes = $utf8.GetBytes($data)

$aes = [System.Security.Cryptography.Aes]::Create()
$rcb = $utf8.GetBytes($rcp)
$aes.Padding = [System.Security.Cryptography.PaddingMode]::Zeros
$enc = $aes.CreateEncryptor($rcb, $rcb)
$out = $enc.TransformFinalBlock($bytes, 0, $bytes.Length)
$enc.Dispose()

# the DLC-content is a concatenation of the base64-string of the encrypted data 
# plus the base64-string of the RC which corresponds to our initial RCP-key.
$data = [System.Convert]::ToBase64String($out)
write-host "$data$rc"

And here a correct XML-format of a decrypted DLC container. All(!) shown values here (strings/numbers/dates) must be in base64-format. I just decoded them all to make it a bit easier to understand them. Some elements or values might be optional, some may be subject of change. I have not tested that in details. It is just a readable format of a single DLC-file I created with JDownloader:

<dlc>
    <header>
        <generator>
            <app>JDownloader</app>
            <version>43307</version>
            <url>http://jdownloader.org</url>
        </generator>
        <tribute/>
        <dlcxmlversion>20_02_2008</dlcxmlversion>
    </header>
    <content>
        <package category="various" comment="" name="Packagename">
            <file>
                <url>http://appwork.org/projects/DLCAPI/dlcapi_v1.0.rar</url>
                <filename>dlcapi_v1.0.rar</filename>
                <size>5838</size>
            </file>
        </package>
    </content>
</dlc>