Security is an important issue in the era of IoT, where a large number of devices are connected. In this paper, we propose a design to enhance the security of the IoT connection using SoC FPGA platforms. The design is a successful combination of the powerful processing and system management capabilities of ARM processors and the flexibility and customizability of FPGA technology. Particularly, we have developed a Digital Signature cryptosystem on a DE10-Standard SoC FPGA board using the built-in ARM processor core and two self-developed IP cores acting as 1024-bit RSA and 256-bit SHA co-processors. Furthermore, we also applied the DMA technique to achieve high-speed data transfer. As a result, the proposed cryptosystem is compact but achieves high performance even with low frequencies. In more detail, the DMA operating at the frequency of 150 MHz can achieve a speed of 1200 Mbps. Also, the 1024-bit RSA core and the 256-bit SHA operating at the frequencies of 50 MHz and 100 MHz have throughputs of 25 Kbps and above 700 Mbps, respectively.