The security of Internet of Things (IoT) devices is one of the most important problems. The processing ability of IoT devices is limited, therefore a more light-weight and secure cryptography is necessary. This paper shows the implementation of 256-bit Elliptic Curve Cryptography (ECC) on an 8-bit microcontroller by applying towering for extension field of degree 32. The authors use a twisted Montgomery curve with a Montgomery ladder which enables fast calculations without inverse elements. In addition to that, this implementation is considered resistant to the Side Channel Attack (SCA) since it applies the Montgomery ladder for the scalar multiplication (SCM). This ECC implementation on Arduino UNO, an 8-bit microcontroller board, takes 3 seconds for an SCM which can be made faster by careful assembly implementation.