I recently stumbled upon the following definition for a hash function:
To get this we define $\hat{h}=\hat{h}_{r}: {\{0,1\}}^* \rightarrow {\bf Z}_R$ as follows: $$ \hat{h}_r(m) = ({\sum_{i=1}^{k} m_i \cdot r^{i-1}}) \bmod R $$ where $R$ is a 161-bit prime, $r$ (the key of $\hat{h}$) is a uniformly distributed element in ${\bf Z}_{R}^*, [...]$
Source: http://www.wisdom.weizmann.ac.il/~naor/p_r_func/pr/pr.html
As far as I understand, $\textbf{Z}_R$ is the additive group of integers $\mod R$. Is this the case?
If so, then what is $\textbf{Z}^*_R$?