Generate random numbers whose sum is equal to a constant value modulo n
For $i=1, \dots, n-1$, generate $n-1$ random numbers $u_i \in [0,2^{κ+1})$ and define $u_n = \left(c - \sum_{i=1}^{n-1} u_i\right) \bmod 2^{κ+1}$.