Due to severe power and timing constraints of the ‘things’ in the Internet of things (IoT), cryptography is expensive for these devices. Custom hardware provides a viable solution. However, these implementations of cryptographic algorithms in the devices need to be upgraded frequently compared to the longevity of these “things”. Therefore, there is a critical need for re-configurable, low-power and high-performance cryptography implementations for IoT. In this paper, we propose to use FPGA as the reconfigurable substrate for cryptographic operations. We demonstrate our proposed approach on a Zedboard, which has two ARM cores and a Zynq FPGA. The implemented cryptographic algorithms include symmetric cryptography, asymmetric cryptography, and secure hash functions. We also integrate our cryptographic engines in SSL library to inherit the support for block cipher modes implemented by OpenSSL. Our approach shows that the FPGA-based reconfigurable cryptographic components consume 1.8x~4033x less energy and run 1.6x~2983x faster than the software implementation. At the same time, the FPGA implementation of cryptographic operations is more flexible compared to custom hardware implementations of cryptographic components.