Oppel-2: A new family of FCSR-based stream ciphers

This paper presents a new family of secure, small and fast stream ciphers referred to as Oppel-2. Oppel-2 uses Feedback with Carry Shift Registers in combination with an output function to produce pseudorandom keystream. Members of Oppel-2 family of ciphers can also be tailored for different applications to meet their implementation constraints while providing required level of security. The paper defines three instances of Oppel-2, which are referred to as Oppel-2 V₀, Oppel-2 V₁ and Oppel-2 V₂. These instances of Oppel-2 provide security of 2⁶⁴, 2⁸⁰ and 2¹²⁸ primitive operations, respectively. The paper also shows that Oppel-2 is immune to linearisation attacks, which are considered as most effective attacks against those ciphers whose theory depends upon properties of 2-adic numbers. In addition the paper also presents a security strength analysis of Oppel-2 against various other types of attacks. This analysis shows that Oppel-2 family of ciphers is suitable for implementation in practical applications.