A blockchain isn't necessary because there's no double spending to prevent. Just broadcasting signed assertions to a bunch of nodes who make all of the data available to the public should be enough for everyone to know who claimed what and when. Less like Bitcoin, more like Certificate Transparency.
>A blockchain isn't necessary because there's no double spending to prevent.
A "chaining of hashes of the previous blocks" has other uses than preventing double spending of currency. It also acts as a "incrementing clock" of record-keeping that's resistant to tampering.
E.g. The "blockchain" started by Surety[1][2] in 1995 in The New York Times published hashes that depended on previous hashes. They could have published hashes that were independent of previous hashes but they didn't. It would not provide the same anti-tampering guarantees.
(I'm only replying to your assertion about blockchain's "double spending" use case in isolation and not commenting on whether the thread's article is a good idea.)
It seems like any distributed system that involves any cryptography these days is being called a blockchain. The Vice article is simply wrong. Yes, it's a great idea to use a chain of hashed timestamps+data to prevent data from being tampered with later. People have been doing this with logs for ages.
The NYT timestamp system doesn't meet the blockchain definition, at least so long as the word has any real meaning. This point is often debated, but my take is that without also featuring some kind of consensus mechanism to order the writes in a specific manner, thus preventing double spending, then the protocol shouldn't be described as a blockchain at all.
A timestamp service (as opposed to a blockchain) is good enough for the goals described in the article. There's no need to enforce strict ordering of transactions because there's no spending. It's just assertions of some fact at some time. So all that's needed are a few reliable servers run by different parties that will log the data. If one of them cheats, it is detectable.
Knowing who is behind the private keys signing the assertions is a far more important problem in this kind of system, and blockchains don't help that one bit.
>It seems like any distributed system that involves any cryptography these days is being called a blockchain. The Vice article is simply wrong. [...] The NYT timestamp system doesn't meet the blockchain definition, at least so long as the word has any real meaning.
My point isn't that Surety is a "formal" blockchain by some rigorous definition. (Obviously the VICE article is taking artistic liberties with the word "blockchain" to retroactively label Surety's published hashes back in 1995.)
The purpose of citing them was only to highlight that dependencies on past hashes accomplishes a different tamper-proof guarantee than your idea of just broadcasting digitally signed assertions.
>There's no need to enforce strict ordering of transactions because there's no spending. It's just assertions of some fact at some time.
Putting extra cryptographic mechanisms around the notion of "at some time" is the motivating reason for a chain of hashes. If Surety didn't chain their hashes and then publish the hash, that's weaker than broadcasting independent hashes.
>Knowing who is behind the private keys signing the assertions is a far more important problem in this kind of system, and blockchains don't help that one bit.
I think I see why you believe focusing on digitally signed assertions is enough security. E.g. the web browser TLS/SSL https security works fine on broadcast assertions with no "blockchain". That's true. It's "trust of a identity hierarchy" rather than "trust of a timeline". The difference is that when users log into "paypal.com" today to withdraw money, they don't care what the private/public certificate authority keys were 3 years ago. However, the users of the database of clinical results do care about past history.
I'm not disagreeing with any of that. All I'm saying is that a chain of hashes is not a blockchain.
Also, we do care what paypal’s certificate was in the past. That’s why we have CT to catch CAs that mess up. We just don’t need to use a blockchain for it to work.
>All I'm saying is that a chain of hashes is not a blockchain.
And to be clear, I wasn't claiming that "chain of hashes" was equivalent to a blockchain. (E.g. bitcoin-like blockchain.) Instead, I extracted one particular property of a blockchain -- the chain of dependent hashes -- to contrast your proposed broadcast solution.
To add to the confusion, it turns out the authors may be implementing your non-Bitcoin suggestion anyway. (See further down in my comment.)
>Also, we do care what paypal’s certificate was in the past.
I understand the nitpick but I mean that web browsers don't care what the particular values were several years ago (especially anything before 2013 since CT didn't exist until then while SSL/TLS existed since 1995). They check existence in a CT log.
>Less like Bitcoin, more like Certificate Transparency.
It looks like the authors propose a architecture more similar to CT than Bitcoin anyway. Excerpt from their proposal:
>We chose to give data storage control to the regulator, as opposed to distributing data storage to nodes across participants in the network like in Bitcoin applications. We preferred this design because the trial regulator is the only party that can and must be trusted, since this party is the one having final approval over success or rejection of the treatment. It is a central authority that cannot be eliminated. We feel implementing distributed storage to everyone in the network (such as that used for Bitcoin) does not fit this regulatory context well, and is also impractical as all parties would also have to locally store data pertinent to the clinical trial on their machines.
I believe this means the remaining issue is that you disagree with the authors calling something "blockchain" that doesn't have a distributed consensus mechanism to prevent double spending.
relabeling everything "blockchain", especially things with lots of established use before the existence of blockchains doesn't seem to have an real value outside of marketing obfuscation, at least to me.
Block chaining -- that specific wording, used in cryptography -- has been around for almost 50 years and is widely known. It's not relabeling and it's not going away.
