The goal is to allow a user to anonymously share sensitive information which can be used in a selection process. The user must be able to prove they were admitted without revealing their sensitive information. A two-step ring signature process meets these requirements.
Consider a group of n users where each user i has a public, Pi, and secret (private) key, Si. A ring signature allows a user to sign a message using their private key, s = sign(m, Si, P1, ..., Pn), proving that they are a member of the group without revealing their identity.