Security Analysis of WG-7 Lightweight Stream Cipher against Cube Attack
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Welch–Gong (WG) is a hardware-oriented LFSR-based stream cipher. WG-7 is a version of the eStream submission Welch–Gong, used for RFID encryption and authentication purposes. It offers 80-bit cryptographic security. In modern days, almost all ciphers achieve the security by exploiting the nonlinear feedback structure. In this paper, we investigate the security of the nonlinear feedback-based initialization phase of the WG-7 stream cipher using the conventional bit-based division property of cube attack, by considering the cipher in a non-blackbox polynomial setting. In our work, we mount the cube attack using mixed-integer-linear-programming(MILP) models. The results of our attack enable us to recover the secret key of WG-7 after 20 rounds of initialization utilizing 2^10 keystream bits in 2^73 time. We show that our proposed attack takes significantly lower data complexity. To the best of our knowledge, our attack is the first one that investigates the security of the nonlinear feedback-based initialization phase of WG-7 cipher.
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