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Comment by m00dy | Hacker News Reader

Blockchain is a very generic term nowadays. E.g. A linked list is also a blockchain.

I don't know that I would go quite that far. A blockchain is a linked list, but IMO a run-of-the-mill linked list doesn't quite make the cut to be a blockchain because I would argue that the essence of the word "blockchain" has to do with the "one block contains the hash of the previous block" property. A C-style linked list where the link is a pointer to a memory location would not be a blockchain.

That being said, I will definitely agree with you that the word "blockchain" is very overused and underspecified these days. Just because a term is often misused doesn't mean it has no definition. I think most of that is just laziness on the part of whoever is using it and not actual lack of...consensus...on a fairly clear definition.

I agree. The whole point of a blockchain is to make it difficult to change a block after it's been inserted. This is normally done by making subsequent blocks dependent on the value of previous blocks in some way (e.g., hashing). That makes it hard to change an earlier block without also altering every subsequent block, which is a problem of an entirely different order of magnitude than just changing a single block (particularly if generating the hashes is computationally expensive).

A normal linked list has no mechanism to avoid block substitutions. Entries have absolutely no dependence on the contents of previous entries, and can thus be swapped out at will.

I think this is a square is a rectangle but a rectangle isn't a square type of thing. A blockchain is a linked list, but a linked list isn't a blockchain.

Surely one feature of a linked list is you can edit it in the middle? A blockchain is an append-only log or a Merkle tree.

Is it? Just from the hip:

Start with an audit log.

Add tamper detection with a rolling hash: blockchain.

Add multi party consensus: distributed blockchain.

Add some kind of digital signature: web of trust.

Add some kind of proof of work: cryptocurrency.

Heh, looking forward to hear about people being asked in tech interviews to reverse a blockchain.

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