White-box cryptography aims to provide secure cryptographic primitives and implementations for the white-box attack model, which assumes that an adversary has full access to the implementation of the cryptographic algorithms. Real-world applications require highly efficient and secure white-box schemes, whereas the existing proposals cannot meet this demand. In this paper, we design a new white-box block cipher based on addition/rotation/XOR (ARX) primitives and random maximal distance separable (MDS) matrix, white-box ARX (WARX), aiming for efficient implementations in both black- and white-box models. The implementation of WARX in the black-box model is nine times faster than SPNbox-16 from ASI-ACRYPT’16, and the implementation in the white-box model is more efficient than SPNbox-16 and WEM from CT-RSA’17. Moreover, the security of WARX in both black- and white-box models is analyzed, which ensures its practical applicability. The design of WARX shows that ARX primitives and random linear layer can improve the efficiency of a white-box block cipher. This article may inspire more provably secure and efficient white-box block ciphers and help to narrow the gap between provably secure white-box schemes from academia and highly applicable schemes in great demand from industry.