arXiv:2603.19781v3 Announce Type: replace Abstract: Lilliput is a lightweight block cipher based on a Type-2 Extended Generalized Feistel Network (EGFN). Although it has been studied under conventional cryptanalytic techniques, its resistance to fault attacks remains largely unexplored. We present a theoretical differential fault analysis of Lilliput under a random-location nibble fault model. A nonzero nibble fault is injected at the input to round 27, with the injection location uniformly distributed among the 16 state branches and unknown to the adversary. We analyze fault propagation through the EGFN and derive ciphertext-difference conditions to identify the faulty branch. A DDT-weighted calculation yields an overall branch-identification accuracy of approximately 99.9980% under independent uniform sampling of plaintexts, nonzero fault values, and fault locations; simulations of 2^20 random faults give 99.9983%. After identifying the faulty branch, we classify propagation patterns using the injected difference and the intermediate S-box output difference. We then derive DDT-based constraints on last-round and penultimate-round subkeys and intersect candidate sets from multiple faulty ciphertexts. In 2^15 simulation trials, key-recovery success rates exceed 90%, 95%, and 99% with 32, 36, and 46 faulty ciphertexts, respectively. These simulation-based results are not claims of physical fault-injection performance but offer insight into practical fault analysis of Lilliput.