[ineptech]

Unless I'm missing something, what I'm describing satisfies both of these (unless one or both parties are malicious).

[Nevermark]

> (unless one or both parties are malicious)

It should be assumed (for the purpose of evaluating if a system is actually secure) that they both are, and are working together.

Validation can be done cryptographically so that assertions (like age) can be verified by one party, and consumed by another party, without either of those parties being able to tie the combination together, even if they are actively cooperating.