Symmetric ciphers purposed for Fully Homomorphic Encryption (FHE) have recently been proposed for two main reasons. First, minimizing the implementation (time and memory) overheads that are inherent to current FHE schemes. Second, improving the homomorphic capacity, i.e. the amount of operations that one can perform on homomorphic ciphertexts before bootstrapping, which amounts to limit their l...

This paper provides an overview of the state of the art in the design of cryptographic algorithms. It reviews the different type of algorithms for encryption and authentication and explains the principles of stream ciphers, block ciphers, hash functions, public-key encryption algorithms, and digital signature schemes. Subsequently the design and evaluation procedures for cryptographic algorithm...

Well-designed initialisation and keystream generation processes for stream ciphers should ensure that each key-IV pair generates a distinct keystream. In this paper, we analyse some ciphers where this does not happen due to state convergence occurring either during initialisation, keystream generation or both. We show how state convergence occurs in each case and identify two mechanisms which c...

In Fast Software Encryption (FSE) 2015, while presenting a new idea (i.e., the design of stream ciphers with the small internal state by using a secret key, not only in the initialization but also in the keystream generation), Sprout was proposed. Sprout was insecure and an improved version of Sprout was presented in FSE 2017. We introduced Fruit stream cipher informally in 2016 on the web page...

Many modern stream ciphers consist of a keystream generator and a key schedule algorithm. In fielded systems, security of the keystream generator is often based on a large inner state rather than an inherently secure design. Note, however, that little theory on the initialisation of large inner states exists, and many practical designs are based on an ad-hoc approach. As a consequence, an incre...

In this paper we present two new n-quasigroup stream ciphers based on new n-quasigroup encryption scheme. Also, we present a practical implementation of these ciphers that has very good cryptographic properties. The implementation is based on a design concept of mixing two ”incompatible” group operations on the set Z28 .