The paper describes a device-level encryption approach for implementing intrinsically secure non-volatile memory (NVM) using resistive RAM (ReRAM). Data is encoded in the ReRAM filament morphology, making it robust to both electrical and optical probing methods. The encoded resistance states are randomized to maximize the entropy of the ReRAM resistance distribution, thus providing robustness to reverse engineering (RE) attacks. Simulations of data encryption and decryption using experimental data from Ru(BE)/ALD-HfO 2 (MO)/Zr/W(TE) ReRAM devices reveals an uncorrected bit error rate (BER) < 0.02 and a maximum key entropy of ≈ 17.3 bits per device. A compensation procedure is also developed for maintaining BER in the presence of temperature changes.