Let's all operations are done on $\mathtt{F}_p$ where $p$ is a large non-prime number.

To mask a value: $a$, we do the following:

1- pick a uniformly random value: $r$, from the field.

2- do as follows: $c= r+a \bmod p$.

Question: is above one-time pad secure?

Let's assume all operations are done on $\mathbb{Z}_p$ where $p$ is a large non-prime number.

To mask a value $a$, we do the following:

1. Pick a uniformly random value: $r$, from the ring.

2. Do as follows: $c= r+a \bmod p$.

Question: Is the above one-time pad secure?