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Comment by cbr | Hacker News Reader

    If you follow GDPR strictly you would need to be
    able to purge the data from your backups.
    Now most backups are considered immutable, so
   you aren't going to do that

Encrypt with a user-specific key, and destroy that key to drop all backups concerning that user.

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This only applies to home grown backup systems. If all you're doing are VM backups of your SQL database there's 0% chance you have the granularity to delete a single user.

"Then don't do that"

Sure, but now you actually have an imposition because the ability to do this kind of thing can't be done on any commercially available backup system.

Don't assume the law makes a distinction between data which is destroyed and data which is irretrievable. I can easily see someone arguing that the data is not destroyed -- there's simply a very, very low chance that anyone will be able to retrieve it. You and I both know that argument makes no sense, but hey, it's the law -- it doesn't have to make sense, it just has to convince a few people with power that you're wrong.

A similar scheme is used to erase data on SSD. Otherwise, you can't reliably delete any data from them.

If the key required to decrypt your backups isn't backed up, you don't have backups. If it is, you're back to the original problem.

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