Weak-keys and key-recovery attack for TinyJAMBU

In this paper, we study NIST lightweight 3 rd round candidate TinyJAMBU. The core component of TinyJAMBU is the keyed permutation P n , which which is based on a non-linear feedback shift register. By analysing this permutation carefully, we are able to find good cubes that are used to build distinguishers in the weak-key setting. These distinguishers outperform the best-known distinguishers, which were proposed in the esteemed Nature Scientific Reports by Teng et al. We also study the exact degree in nonce of the feedback polynomial of P n. This helped us in concluding that TinyJAMBU with more than 445 rounds is secure against distinguishers using 32 sized cubes in the normal setting. Finally, we give new key-recovery attacks against TinyJAMBU using the concepts of monomial trail presented by Hu et al. at ASIACRYPT 2020. Our attacks are unlikely to jeopardise the security of the entire 640 rounds TinyJAMBU, but we strongly anticipate that they will shed new lights on the cipher’s security.