In an embodiment, a verifier receives requirements for membership in a group from a service and receives proof of attributes from users. The verifier verifies whether the proof of attributes meets the membership requirements and sends acceptance or rejection to the service. If the proof meets the requirements, the service allows the users to become members of the group and allows the members to transfer data to and from other members. If the proof does not meet the requirements, the service prevents the users from becoming members. In this way, the service and group members know that other group members satisfy the group membership requirements without needing to know the identity of the group members or other information unrelated to the group membership requirements.