This paper introduces a zero-overhead encryption and authentication scheme for real-time embedded multimedia systems. The parametrized construction of the Discrete Wavelet Transform (DWT) compression block is used to introduce a free parameter in the design. It allows building a keyspace for lightweight multimedia encryption. The parametrization yields rational coefficients leading to an efficient fixed point hardware implementation. A clock speed of over 240 MHz was achieved on a Xilinx Virtex 5 FPGA. Comparison with existing approaches was performed to indicate the high throughput and low hardware overhead in adding the security feature to the DWT architecture.