TITLE: Notation: "belongs to" with an R subscript
QUESTION [6 upvotes]: I've run into an expression:
$x_i \in_R \mathbb{Z}_q$
– and I wonder what this means. 
An example paper is here, here's example in Wikipedia.
Can anybody help me? Thanks in advance.

REPLY [2 votes]: $x \in_R S$ means $x$ is chosen uniformly randomly from $S$. This notation is common in cryptography papers. For example, this notation is defined in the beginning of section 2 of Proofs that yield nothing but their validity and a methodology of cryptographic protocol design.