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  "value": {
    "text": "Differential Fault Attacks on TFHE-friendly cipher FRAST (Weizhe Wang, Deng Tang) ia.cr/2025/771",
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          "alt": "Abstract. Differential Fault Attacks (DFAs) have recently emerged as a significant threat against stream ciphers specifically designed for Hybrid Homomorphic Encryption (HHE). In this work, we propose DFAs on the FRAST cipher, which is a cipher specifically tailored for Torus-based Fully Homomorphic Encryption (TFHE). The round function of FRAST employs random S-boxes to minimize the number of rounds, and can be efficiently evaluated in TFHE. With our specific key recovery strategy, we can mount the DFA with a few faults. Under the assumption of precise fault injection, our DFA can recover the key within one second using just 4 or 6 faults. When discarding the assumption and considering a more practical fault model, we can still achieve key recovery in a few minutes without increasing the number of faults. To the best of our knowledge, this is the first third-party cryptanalysis on FRAST. We also explored countermeasures to protect FRAST. Our analysis revealed that negacyclic S-boxes, a key component of TFHE-friendly ciphers, are unsuitable for incorporating linear structures to resist DFA. Consequently, we recommend removing the negacyclic restriction in the penultimate round of FRAST and introducing non-zero linear structures into the S-boxes of the last two rounds. We believe that our work will provide valuable insights for the design of TFHE-friendly ciphers.\n",
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    "createdAt": "2025-05-03T20:15:05.077155Z"
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