mask query dynamic query string value

Question

I am building a wrapper to process payments. We want to log requests, but don't want to store sensitive credit card data. A query string will be passed similar to what is below

amount=100.00&expMonth=01&expYear=14&cardnumber=4111111111111111

I want to mask the first 12 digits of the credit card number with X values. However, the cardnumber key will not always be in the same spot.

My first leaning is to create a NameValueCollection and check for the key and do a string.format("XXXX-XXXX-XXXX-{0}", substring of the value

var qs = HttpUtility.ParseQueryString(request);
foreach (string key in qs)
{
    if (key == "creditcard")
    {

    }
}

Can someone point me in the right direction?

I need to save the string in the same format with just the credit card number masked.

Answer 1

This works great, there may be a more elegant solution though.

var maskedRequest = "";
var qs = HttpUtility.ParseQueryString(request);
foreach (string item in qs.AllKeys)
{
   if (item != "cardnumber")
   {
       maskedRequest = maskedRequest + item + "=" + qs.Get(item) + "&";
   }
   else
   {
       maskedRequest = maskedRequest + item + "=" + string.Format("XXXX-XXXX-XXXX-{0}", qs.Get(item).Substring(12, 4)) + "&";
    }
}

maskedRequest = maskedRequest.Remove(maskedRequest.Length - 1)