Security of data transferred on the Wireless Sensor Network is of vital importance. In public
key cryptography RSA algorithm has been used for a long time, but it does not meet the constraints of
WSNs. Elliptic Curve Cryptography(ECC) has been employed recently because of its highest security for
same length bit. ECC point multiplication operation is time consuming which affects the speed of
encryption and decryption of data. Security in WSNs is addressed in our work, where a modified ECC is
designed by performing the point multiplication using Montgomery multiplication technique that
achieves considerable speed and with reduced area utilization. The ECC is first simulated on different
FPGA devices, with key length 11, 112, 131 and 163 bits and the area-speed tradeoff is compared. ECC
algorithm is implemented with software and hardware choosing Artix 7 XC7a100t-3csg324 FPGA which
supports key lengths of 11, 112, 131 and 163 bits. When implemented on a Artix 7 FPGA, it completes 163
bit data encryption operation over GF(2163 ) in 1ms with the maximum frequency of 229MHz.
The ECC algorithm is reconfigurable with low level to high level security with different bit key sizes.
The proposed ECC algorithm modeled using VHDL and synthesized on Spartan 3 and 6, Virtex 4, 5 and
6 and Artix7 before the hardware implementation on Atrix 7. The design satisfies the needs of resource
constrained devices by decreasing the encryption and decryption time to 1 ms with equal keylength and
datasize, while device utilization is within 13%
