I am implementing in C++ the Scream stream cipher. The Scream family is composed of Scream-0, Scream-S and Scream-F. For this question, assume that I'm using Scream-S.
The specifications of the Scream cipher are given in the paper "Scream: a software-efficient stream cipher", but I didn't find a reference sourcecode for this cipher which could have helped me.
Maybe because the specs include many notations, I have some questions about the scream cipher:
In section 2 about the two 2X2 matrices : Am I right to say that $x$ and $x+1$ (from the $GaloisField(256)$) are replaced respectively by $2$ and $3$?
In section 3, it's possible to implement the function $F$ to optimize it. The author didn't define the multiplication ($u0 = M1(0,0) . S1[x]$). Is it a multiplication following $GF(256)$ with the polynomial $x^8 + x^7 + x^6 + x + 1$ (0x1C3) ?
In the algorithm of $F$ in section 3, they write 'byte0'. Does $byte_0$ refer to the MSB or LSB of an integer ?
Since $F$ is the core of the algorithm, it's important for me to know and understand these kind of details.