Elliptic curve cryptosystems (ECCs) may be chosen instead of RSA in secure embedded systems, thanks to shorter keys. However, ECC may be vulnerable, as any other cryptographic implementation, to side channel analysis, which may reveal secret information by analyzing collateral sources of information, such as power consumption. To protect the device against Timing, Simple and Differential Power Analysis, we propose the implementation of a new scalar multiplication algorithm based on randomized windows method.