International Association
for Cryptologic Research

It is shown that the stream cipher proposed by Carlet and Sarkar in ePrint report 2025/160 is insecure. More precisely, one bit of the key can be deduced from a few keystream bytes. This property extends to an efficient key-recovery attack. For example, for the proposal with 80 bit keys, a few kilobytes of keystream material are sufficient to recover half of the key.