[derefr]

I think you're talking about different use-cases than the person you're replying to.

A distributed immutable ledger has many uses other than recording voluntary transactions, or even recording things to do with specific people.

For example, such a ledger can be used to create a tamper-proof security-camera footage log. Just hashes of exported video files, locked into a chain at time of export. You can redact the videos themselves (i.e. make all copies of the referenced video unavailable), but you can't change the hash, and so there's no party you can collude with to substitute one video for another. Even if you're a state actor. You either have the videos — which can be proven to be the right videos — or you don't; but you'll never be able to present the wrong videos.

Or, in the same vein, a chain-of-custody log for the contents of a safety deposit box at a bank. Any time someone opens the box, an entry is automatically appended to the log saying what authorization (e.g. access card) was used to open the box. Once again, the fact that the log is distributed on a wider multi-party-controlled system, makes it impossible (or at least impractical) for the bank itself to tamper with the logs to steal something from your box.

These are "finance" / "security" / "financial security" use-cases. But they're not PII. There's no point at which any of this data would ever legally require redaction or purging, because it doesn't relate to a specific client profile. It relates either to metadata of public-point-of-view sensory data capture; or it relates to employee actions against customer accounts, where the mapping back to an individual isn't given in the public log but rather exists in a private database.

[sangnoir]

> For example, such a ledger can be used to create a tamper-proof security-camera footage log.

What's the use-case here - who are the untrustworthy individuals that society needs to protect itself against? Societal trust is currently rooted in people - it will not be switched over to machines/distributed ledgers any time soon. This is why people can write affidavits/get sworn in to say "That video's legit" under pain of perjury. Frankly, there's little money in turning over trust to a blockchain when there is an individual/organization that can be interrogated. It's not perfect, but trying to perfect it has (evidently) diminishing returns

[derefr]

That example is not about positive proof (i.e. proving that real evidence is real); it's about negative proof (i.e. proving that fake evidence is fake.) It's about having a way to figure out that the expert defending the evidence has been bribed, and is saying what the prosecution wants them to say.

You can't charge someone with perjury if you can't prove the faked evidence is faked—which is why so few people get charged with perjury. Any threat of perjury with no discriminatory proof mechanism to back it up, is toothless, and experts will treat such threats with exactly the respect they deserve. (Look at the Japanese court system if you don't believe me.)