Logic encryption is a hardware security technique that uses extra key inputs to prevent unauthorized use of a circuit. With the discovery of the SAT-based attack, new encryption techniques such as SARLock and Anti-SAT are proposed, and further combined with traditional logic encryption techniques, to guarantee both high error rates and resilience to the SAT-based attack. In this paper, the SAT-based bit-flipping attack is presented. It first separates the two groups of keys via SAT-based bit-flippings, and then attacks the traditional encryption and the SAT-resilient encryption, by conventional SAT-based attack and by-passing attack, respectively. The experimental results show that the bit-flipping attack successfully returns a circuit with the correct functionality and significantly reduces the execution time compared with other advanced attacks.