Double-A -- A Salsa20 Like: The Design

This paper discusses the design choices of the sponge constructed cryptographic hash function Double-A. Firstly, the relative advantages of why a stream mode cipher is used rather than a block mode cipher are given. Secondly, a description of what a sponge function is, how it is designed and what are its main components. Finally, after a brief recall of the Salsa20 stream cipher and its structure, the choices of the states width, rounds and operations in the pseudorandom function f are discussed in detail to show how and why they are used in the permutation of Double-A.