Blockchain and user rights to ask for personal data removal Some countries (France with the CNIL, and more generally European - but probably many other - countries) have laws that give the right to users of online services to ask for permanent unsubscription / personal data removal from their database.

This seems impossible with a blockchain technology: we cannot remove past blocks without breaking the whole structure integrity.

It might not be a problem with BitCoin, for which there is no real personal data (data is linked to a private/public key, not to a username / physical identity), but still those questions might apply more generally to the growing blockchain industry.

How to deal with the legal right of data removal for users in a blockchain paradigm?
In general, cryptocurrency is not an online service separate to the user, the user is a node and is a part of the service. Still, the definition of online service is not a good fit for the most part.

Speaking of Bitcoin, the only personal data is your private keys. Everything else is broadcast at some point, it is like beaming some of your public data into outer space via satellite, bouncing from star to star (node to node) and then saying that you want it taken down. Only your private keys are personal data and they are never broadcast (unless you make a bad mistake outside of Bitcoin!).

If it comes to law, the purpose for deriving your public keys and addresses is to send/receive Bitcoin which requires broadcasting. You can no sooner take it back than you could mistakenly post a valentine in a print newspaper then expect the newspaper to take back all copies and have your public data erased because you have changed your mind.