Round-efficient multiplication

This functionality (which we denote as normal multiplication $\underset{i=1}{\overset{n}\prod}x_i$ and always use in case we need to multiply $>2$ factors) computes the product of $n$ elements. It works as follows:

1. $[r_i \in_R \mathbb{F}_p], \text{ for }i \in \{0 .. n\}$
2. $[s_i] = [r_i / r_{i-1}] \text{ for }i \in \{1 .. n\}$ //this can be computed in the offline phase
3. $[y_i] = [s_i] [x_i] \text{ for }i \in \{1 .. n\}$
4. Open $y_i$, calculate $Y = \underset{i=1}{\overset{n}\prod}y_i$.
5. Output $Y [r_0 r_n^{-1}]$

This also allows to compute running product $x_1; x_1 x_2; ...; x_1 x_2 ... x_n$ in one go using the same method: in step 4 we compute all $Y_k = \underset{i=1}{\overset{k}\prod}y_i$, and then calculate $Y_k[r_0 r_k^{-1}]$