SLBsignature计算问题求助

我使用的是Delphi,SLB signature 计算代码如下：
procedure TForm1.Button1Click(Sender: TObject);
var
  S, U: String;
  L: TStringList;
  I: Integer;
begin
  L := TStringList.Create;
  try
    L.Add( 'AccessKeyId=aaaaaaaa');
    L.Add( 'Action=DescribeLoadBalancers');
    L.Add( 'RegionId=cn-east-hangzhou-01');
    L.Add( 'SignatureMethod=HMAC-SHA1');
    L.Add( 'LoadBalancerId=bbbbbbbbbbb');
    L.Add( 'SignatureNonce=' + LowerCase(dxMakeGUID));
    L.Add( 'Version=2014-05-15');
    L.Add( 'SignatureVersion=1.0');
    L.Add( 'TimeStamp=' + _UTCTime);
    L.Sorted := True; //这里排序
    S := '';
    U := '';
    for I := 0 to L.Count - 1 do
    begin
      if S <> '' then
      begin
        S := S + '&';
        U := U + '&';
      end;
      S := S + L;
      U := U + L.Names + '=' + HTTPEncode(L.ValueFromIndex);
    end;
    S := HTTPEncode(S);
    S := StringReplace(S, '%7E', '~', [rfReplaceAll]);
    S := StringReplace(S, '/', '%2F', [rfReplaceAll]);
    S := StringReplace(S, '+', '%20', [rfReplaceAll]);
    S := StringReplace(S, '*', '%2A', [rfReplaceAll]);
    S :=   'GET&%2F&'+ S;
    S := HMAC_Base64( 'cccccccccc&', S);
    Memo1.Lines.Text := 'http://slb.aliyuncs.com/?' + U + '&Signature=' +  HTTPAPP.HTTPEncode(S);
  finally
    L.Free;
  end;
end;
我怎么得出的值都不对，返回错误信息为” The request signature does not conform to Aliyun standards.“，
其中 HMAC_Base64('xxx&', 'aabbcc')为"lJXHNIeUWE0/g9+jZRD5WhSa3sI="(key为xxx&，信息为aabbcc)

请大家帮忙看看是我的HMAC_Base64计算的值的问题呢还是我参数的问题