This paper presents a reconfigurable hardware architecture for Public-key cryptosystems. By changing the connections of coarse grain Carry-Save Adders (CSAs), the datapath provides a high performance for both RSA and Elliptic Curve Cryptography (ECC). In addition, we introduce another reconfigurability for the flip-flops in order to make the best of hardware resources. The results of FPGA implementation show that better performance is obtained for ECC on the same hardware platform.