why would that need a blockchain (even without proof of work), as opposed to simple signed, timestamped, indexed posts and having the reading client app check the signature and post indices?
> why would that need a blockchain (even without proof of work), as opposed to simple signed, timestamped, indexed posts and having the reading client app check the signature and post indices?
It depends on how the message is signed. If the message format's this:
sign_message(message + timestamp + index) + message + timestamp + index
The 'index' can be manipulated: The signer (malicious or not) can resign an old message & effectively overwrite a previous message.
sign_message(new_message + old_timestamp + old_index) + new_message + old_timestamp + old_index
This means that in the event of such a resigning, it's the app's responsibility to prevent resigned messages from overwriting old messages.
Blockchains prevent this at the data structure level because signature hashes are effectively random, meaning they're near-impossible to tamper with:
whole_message := prev_message_hash + sign_message(message + timestamp) + message + timestamp
wherein prev_message_hash := hash(prev_whole_message)
In contrast, this here, which is the only thing the blockchain struckture really adds:
> The signer (malicious or not) can resign an old message & effectively overwrite a previous message
… is a rather radical shift of the goalpost, as the only capability the blockchain really adds is to protect against modification not by untrusted intermediaries (which was the purpose and which would already be covered without a blockchain) but by the legitimate owner/editor of the feed.
In other words: The only thing the blockchain adds is that it makes it impossible for YOU as the user to edit YOUR OWN posts. I'm not sure that's something most people in the social network context (as opposed to, say, a financial transaction ledger) would see as a feature and not an anti-feature.
Yeah, that's exactly what SSB does, plus each post includes a hash of the previous post.
I think that's so that even the holder of the private key can't retroactively replace an old post with an altered version of that post (but with the same index number and similar timestamp).
Feels like people are really just trying to play into "everyone has a number that can be banned" for the Internet/social life in general.