Modify security level of a sub-task

In our organisation we use JIRA as the issue tracker between us (developers) and our customers.

Quite often, an issue is opened which describes the overall change required which contains all the information that all parties should see.

However, when it comes down to doing the work, we would like to use sub-tasks to assign development tasks to our developers. The customer should not see these tasks.

Therefore it would be desirable to change the security level of the sub-tasks so that the customer does not see them.