Practical Key-Recovery Attack on MANTIS5

MANTIS is a lightweight tweakable block cipher recently published at CRYPTO 2016. In addition to the full 14-round version, MANTIS7, the designers also propose an aggressive 10-round version, MANTIS5. The security claim for MANTIS5 is resistance against “practical attacks”, defined as related-tweak attacks with data complexity 2 less than 2 chosen plaintexts (or 2 known plaintexts), and computational complexity at most 2126−d. We present a key-recovery attack against MANTIS5 with 2 28 chosen plaintexts and a computational complexity of about 2 block cipher calls, which violates this claim. Our attack is based on a family of differential characteristics and exploits several properties of the lightweight round function and tweakey schedule. To verify the validity of the attack, we also provide a practical implementation which recovers the full key in about 1 core hour using 2 chosen plaintexts.