Because blockchain is decentralized, what would happen if there was no cryptography anymore to protect the blockchain? I know it would not be used anymore but why? "Hackers" could reverse transactions but I can't think of anything else...

  • $\begingroup$ A generic block chain doesn't need to be decentralised. You can have just one block series and it's still a chain. $\endgroup$ – Paul Uszak Nov 14 '18 at 23:17
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    $\begingroup$ @j.loper: The comment by the previous user is nonsense: "decentralized" is intrinsic to the definition of "blockchain", and the second sentence is a non-sequitur. $\endgroup$ – Ella Rose Nov 14 '18 at 23:25
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    $\begingroup$ I have heard of private blockchains sometimes being called "centralized". $\endgroup$ – kodlu Nov 15 '18 at 0:07

Blockchain is a decentralized append-only ledger.

If it does not use cryptography to achieve the goal of being append-only, then it would likely not provide any real guarantee of being append-only. It would only provide such a guarantee as long as it was used as proscribed.

For instance, we could create an append-only data structure in a program, and simply program the api to refuse to make any modifications other than appending new data.

However, that does not guarantee that no other modifications could be made to the underlying data, there could exist many ways to work around the provided api to insert/remove/etc as desired - if you don't use the provided api you can do anything you want to the underlying data. If there is no form of cryptography protecting the integrity of the information, then any peers that attempt to read this data structure have no way of knowing it has been tampered with.

Without cryptography, "append-only" is more of a suggestion/recommendation rather than a matter of technical capability. It is merely inconvenient rather than computationally intractable.

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  • $\begingroup$ One idea worth exploring is that fact that the work factor is tunable, and why is it at the current value? What happens if the work factor is too low? "No crypto" is just the extreme end of a continuum. $\endgroup$ – bmm6o Nov 16 '18 at 22:45
  • $\begingroup$ @bmm6o What current value? They're all different. Anyway, the work factor only applies to currencies, not generic chains like Medicalchain where the only fundamental requirement is that a non invert able hash links the blocks together. All else stems from that. In a currency, it would almost certainly crash financially. It would be the digital equivalent of alchemy wrt the gold price. Although to be honest, no one probably knows for certain as there's only 2 or 3 salient examples so far. The currency forum is a more knowledgeable place for exploring this idea. $\endgroup$ – Paul Uszak Nov 17 '18 at 23:48

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