Question

I've been working on the design of a longitudinal study and one requirement is:

- all participants will have a unique identifier that
- is not reversible from the data storage/analyst side of the study
- is defined by something easily remembered by a participant that is relatively static over several years, ex. a participant's proper name and birth date in a given format.
- Creation of the unique identifier will occur on the participant's computer and no portion of the defining string will be sent with other collected data

How do I go about meeting this goal?

Initial thoughts are to use bcrypt or something similar but that runs into the problem that if there is a list of possible participant names and birthdays it becomes trivial to determine who participated and their answers. This hypothetical situation is not very likely but concerning.

I've looked into ID based cryptography as a possible answer but the increase in complexity and high likelihood of user error are prohibitive.

Am I missing a simple answer?