Remove Class Id Attributes Of All Tags In Given Html Posted

I have a fck editor in which the user enters some text. And in the code i want to strip the class,id attributes of the text posted. I know this can be done through regular expressions And i have written some code to do so but unfortunately it's not working.

private string RemoveScripts(string input)
{
string re1 = "(.*?"; // Non-greedy match on filler
string re2 = "(class)"; // Word 1
string re3 = "(=)"; // Any Single Character 1
string re4 = "(".*?"))"; // Double Quote String 1
string re5 = "(id)";
Regex regClass = new Regex(re1 + re2 + re3 + re4, RegexOptions.IgnoreCase | RegexOptions.Singleline);
Regex regID = new Regex(re1 + re5 + re3 + re4, RegexOptions.IgnoreCase | RegexOptions.Singleline);

input = regClass.Replace(input, new MatchEvaluator(ReplaceClassID));
input = regID.Replace(input, new MatchEvaluator(ReplaceID));
return input;
}
private string ReplaceClassID(Match m)
{ return ""; }