[danpat]

It can be achieved with a zero-knowledge proof - there are many schemes, but in essence, they all allow you to prove something (e.g. your birthdate, validated by a government agency), without revealing who you are. You can prove to a third party "the government authenticated that I was born on 1970-01-01" without exposing who "I" is.

Some worthwhile reading on the topic if you're interested:

https://en.wikipedia.org/wiki/Zero-knowledge_proof#Zero-Know...

https://en.wikipedia.org/wiki/Blind_signature

It should even possible to construct a protocol where you can prove that you're over 18 without revealing your birthdate.

Zero-Knowledge Range Proofs: https://eprint.iacr.org/2024/430

"Zero-knowledge range proofs (ZKRPs) allow a prover to convince a verifier that a secret value lies in a given interval."

[selcuka]

ZKP is better, but still not foolproof. Depending on the implementation, the government may now know that you have an account, or at least attempted to open an account on that service. You will have a hard time denying it in the future if the government asks to see your posts (as the US is currently doing at their borders).

[bawolff]

> ZKP is better, but still not private. The government now knows that you have an account, or at least attempted to open an account on that service

Umm, no. That is not how a scheme like this would work.

[bawolff]

> It should even possible to construct a protocol where you can prove that you're over 18 without revealing your birthdate.

Not just theoretically posdible, people have done it: https://zkpassport.id/

[lukan]

Sounds interesting, but:

"This is experimental software. While it has undergone external review, it has not yet received a formal security audit. Please use with caution and at your own risk in production environments."