## Cryptology ePrint Archive: Report 2019/920

Related-Key Differential Slide Attack Against Fountain V1

Raluca Posteuca

Abstract: The stream cipher FOUNTAIN was introduced in April 2019 as one of the candidates in the NIST lightweight crypto standardization process. In this paper we introduce a slide attack that leads to the construction of 32 relations on key bits, with time complexity around $17\times 2^{80}$. The success of the attack is around 98%. We also present some properties of the internal state transitions that allow the identification of (key-iv-ad) input data that produce identical ciphertexts, with probability of $2^{-32}$.

Category / Keywords: secret-key cryptography / lightweight cryptography, Fountain, slide attacks, internal states collisions, invertible states transition.

Original Publication (in the same form): RCD-2019