A method for collecting data from a group of entitled members. The method may include receiving, by a collection unit, a message and a message signature; validating, by the collection unit, whether the message was received from any of the entitled members of the group, without identifying the entitled member that sent the message; wherein the validating comprises applying a second plurality of mathematical operations on a first group of secrets, a second group of secrets, and a first part of the message signature; and rejecting, by the collection unit, the message when validating that the message was not received from any entitled member of the group.