Hardware IP protection has been one of the most critical areas of research in the past years. Recently, attacks on hardware IPs (such as reverse engineering or cloning) have evolved as attackers have developed sophisticated techniques. Therefore, hardware obfuscation has been introduced as a powerful tool to protect IPs against piracy attacks. However, many recent attempts to break existing obfuscation methods have been successful in unlocking the IP and restoring its functionality. In this paper, we propose SARO, a Scalable Attack-Resistant Obfuscation that provides a robust functional and structural design transformation process. SARO treats the target circuit as a graph, and performs a partitioning algorithm to produce a set of sub-graphs, then applies our novel Truth Table Transformation (T3) process to each partition. We also propose the $T3_{metric}$, which is developed to quantify the structural and functional design transformation level caused by the obfuscation process. We evaluate SARO on ISCAS85 and EPFL benchmarks, and provide full security and performance analysis of our proposed framework.