微信公众号支付时获取签名 求大神帮忙

///
/// 获取签名
///
/// sin签名
public string getSin(Hashtable ParametersTosin,string appkey)
{
StringBuilder sb = new StringBuilder();
ArrayList akeys = new ArrayList(ParametersTosin.Keys);
akeys.Sort();
foreach (string k in akeys)
{
string v = (string)ParametersTosin[k];
if (null != v && "".CompareTo(v) != 0
&& "sign".CompareTo(k) != 0 && "key".CompareTo(k) != 0)
{
sb.Append(k + "=" + v + "&");
}
}
sb.Append("key=" + appkey);
string sign = MD5(sb.ToString()).ToUpper();
return sign;
}
这是我在网上找的 ，获取的签名是做什么用的