If you remove the LCR and PoW, all you are left with is a toy example which cannot work in practice.
What is needed is education about censensus design and bitcoin's implementation of the solution, rather than a 'how to guide' for building a basic linked list under the guise of 'blockchain'.
Add a field to store a random number.
Keep generating values for this field until the hash of the structure has 'n' leading zeros.
Is that more or less correct?
It's worth adding to that description that the hash must be secure in that it does not allow determining what random number to use to get a particular output (I'm sure you already recognized this detail - it just guarantees you have to keep trying actually random numbers to find a result).
Also worth adding is that the 'n' (Basically the difficulty) is generally going to need some way of scaling based on how quickly correct hashes were found in the past. This is important to prevent problems that would happen with people being able to generate correct results too quickly (Or even just significantly faster then previously).
In particular, Bitcoin's difficulty factor scales such that a new block is found aprox. every 10 minutes, so 'n' is adjusted every so many blocks depending on how fast the hashes were found. Because in the case of Bitcoin, a found block means more coins in the market, it is important that when more hashing power is added, it doesn't result in blocks now being found 1 minute apart. If that were to happen, then you'd have 10 times the number of coins entering the market.
[ed: from other comments, I gather that "passage of time" means "added blocks (hashes)" - but I'm still not clear on where the agreement on what constitutes "in 10 minutes on average" comes from - if A sees an addition to the blockchain of N blocks with X proof-of-work, lets call it N * X from B, and sees M blocks with Y proof-of-work from C -- it should be easy to figure out which is bigger of N * X and M * Y (here we don't really assume multiplication, but some way to figure out maximum proof-of-work).
But how does A know how long either took? Is the time local, so that A looks at the head of the B and C chains, and considers when A saw this head, and figure the elapsed time based on that?]
It's also worth keeping in mind the problem that timestamps are technically forge-able by the miner. Bitcoin doesn't really solve this problem, but it does place requirements that the timestamp of a block be larger then the average of the past 11 (With various constraints). Thus if you presumably have mining distributed enough, then one giving you as invalid of a time as would still be accepted wouldn't end-up affecting things long-term since they can't generate blocks fast enough to heavily affect the average. Still technically an attack vector though.
In that situation, A doesn't care how long it actually took to find those blocks, the scaling of the difficulty/work-factor handles that. A can rely on the fact that (Unless someone introduced or removed a significant chunk of hashing power, or broke the hashing algorithm) the current network difficulty represents the amount of work needed to represent approximately '10 minutes'. PoW below that difficulty isn't accepted, and above that would be considered proving more work then required (But is also, of course, harder to find. So it proves more, but should take longer then 10 minutes for the network to find).
Since Bitcoin calculates the difficulty to result in about 10 minutes between blocks (As I explained in my last comment), that's how long it should approximately take. It's possible B or C got lucky and found it faster then that, but statistically that is unlikely since the hash result is completely random. If significantly more hashing power is added to the network and the blocks are consistently found faster then the target time, then when the difficulty is recalculated later-on (After the 2016 blocks are done) it will go-up, making them again take about 10 minutes with the hew hashing power taken into account.
This sounds pretty interesting, can you elaborate on how exactly its proxy model for the passage of time?
You need an analogue to elapsed time to solve this problem. Hashes in bitcoin are probabilistic, there is an expected number of hashes required to solve the PoW (on average). Each hash takes an amount of time that cannot be made faster, so you suddenly have an unforgeable, easily provable analogue to elapsed time.
Now to actually answer your question: if you take 2 bitcoin blockchains that stem from the same origin block, but blockchainA has 20 blocks with a very easy target "fffffffdab3" and blockchainB has 1 block with a very difficult target "00000000003", then blockchainB has actually done more work than blockchainA, even though it has less blocks (it is "shorter"). So blockchainB has the most cumulative proof of work.
I don't see this any differently than a tutorial that makes a static image move around the screen with key presses. Is it a full game? Not at all. But can it teach you how to build a tiny piece of it, and you can look at other tutorials to figure out how to build other tiny pieces of it, and eventually synthesize that knowledge and make a full game? Yes.
- Hashcash-style proof of work: http://www.hashcash.org/ (originally designed to make spamming harder, although I don't think it ever really became widely adopted).
- Merkle trees to reference transactions in the blocks (same technology used for bittorent chunks): https://en.wikipedia.org/wiki/Merkle_tree
- Elliptic curve cryptography for signing transactions: https://en.wikipedia.org/wiki/Elliptic_curve_cryptography (asymmetric cryptography, used in TLS, SSH etc...)
- When a new "node" connects to the network it uses hardcoded addresses and DNS seeds to find other nodes to connect to: https://bitcoin.org/en/glossary/dns-seed (before that it used IRC)
And there are probably a few other things but basically if you know how to work with those technologies then you have all the tools you need to implement a bitcoin clone. It's nothing groundbreaking, it's "just" a clever novel use of existing technology.
All the actual "rules" of the network (the block reward etc...) are simply validated in the nodes, they'll reject any block that's not properly crafted (i.e. bad reward, invalid proof of work etc...). Therefore the node consensus dictates what bitcoin is. If you implement a non-compatible change in the client and you don't convince all the other users to switch you create a fork since you won't have the same definition of what constitutes a valid block.
Instead this is just a list of hashed-linked documents... Not that much different from a Git repo or a basic file system with integrity checks. Hashing != blockchains.
You are interpreting "blockchain" to be constrained to a "chain of hashes". That is a valid interpretation.
The parent (Uptrenda) is interpreting "blockchain" as a umbrella label for "distributed ledger". This wider definition is also a valid interpretation and this language phenomenon is called "synecdoche".
To point back to the actual article, the author (Gerald Nash) is using "blockchain" in both meanings. On the one hand, he talks about the wider scope of distributed currency... but on the other hand, his Python example is constrained to a "chain of hashes". Since Mr Nash is mentioning the Satoshi bitcoin whitepaper when talking about "blockchain" (the wider meaning), Uptrenda's criticism is reasonable because the most interesting part of distributed-blockchain is the invention of incentives (mining rewards) and social agreement on acceptable hashes (e.g. how many 0000s are counted, which chain is chosen, etc).
As other distributed projects such as IPFS/Diaspora/Sandstorm/etc show, finding the right combination of incentives to create social buy-in and sustainability is the hard part. The hashes is the easy part.
"Block chains" in modern times are very helpful in handling transactions in databases by replacing things like CAS-Numbers  with hashes. The hash of the previous block effectively becomes the CAS-Number, with the feature of staying persistent and verifiable.
CAS example: IF X_version IS 200 SET X=2
BC example: IF hash(X) IS 200 ADD document Y WITH Y_parent = hash(X)
That is, while the article does in fact also mentions Bitcoin, I don't see a point in discrediting the article, the code or the author in any way. Personally, I find it far more valuable for engineers to understand the underlying, fundamental concepts of things before going all-in. Sure, he could have discussed all these things, but for people who are new to the topic, that would not have been very helpful in understanding the concept of a block chain.
Citing historical usage and original meanings is not relevant as to why people use synecdoche.
The point is that in today's discourse, the term "blockchain" has already expanded beyond the original literal technically constrained meaning of "chain of hashes". Even if _you_ want to keep the original meaning of "blockchain", you still have to recognize when _others_ are using synecdoche.
Examples in media:
To interpret those articles correctly, you have to mentally substitute "blockchain" with "distributed ledger". If you substitute with "chain of hashes", the articles make no sense.
Synecdoche throws original historical usage out the window.
>, but for people who are new to the topic, that would not have been very helpful in understanding the concept of a block chain.
There are many web articles that create a "toy" blockchain by showing _hashes_. The problem is that the abundance of such articles actually hides the real ingenuity of the Satoshi/bitcoin.
Again, the hard part is combining multiple technologies in clever ways that can synchronize the psychology of anonymous people -- aka "decentralized trust". The hashing is the least interesting component of all that. However, since the "hashes" are the most "accessible" part of it (especially to programmers), that's what everybody ends up writing about! This has the unintended side effect if hiding the more groundbreaking ideas (the psychology) of distributed ledgers.
It's like what Nick Szabo talks about in his social scalability article. That the design of Bitcoin offers high social scalability, allowing anyone to participate in the system across cultures, languages, customs, and laws. It kind of ties everything together under a single model.
I also agree with you about the "Synecdoche" thing, too. It seems like we're arguing about the same thing. As you say, you can interpret "blockchain" as the chain of blocks that is outputted from the consensus system or as the whole system itself. But I guess in the context of this article it was confusing whether this poster was having a genuine misunderstanding or was just talking about a part of the system.
The idea of a "block chain" had a name back then and it still has a name now. No software developer would confuse a hash list with the underpinnings of a virtual currency unless:
A) You're writing a title for an article and want more clicks
B) You're a banking institution that wants to seem "hip"
C) You're working on a centralized database but really need funding so you throw in the word "blockchain"
D) You're a reporter and you have no clue what you're talking about
Show me anyone referring to a "block chain" in a non virtual currency context that doesn't fall into the above categories and I'll reconsider.
It's kind of like how in modern cryptography most of our algorithms aren't bullet proof. Cryptographers aren't saying that an algorithm can't be broken, but that it requires so much computational resources to do so that its simply improbable. We can say that blockchains also include this idea but they add the economic aspect; Now it isn't just improbable to break an algorithm (with universe sized computers) -- its also improbably (and irrationally) expensive.
Your other point is that a blockchain is simply a linked chain of documents. This is incorrect. The whole point behind a blockchain is that it serves as a way to get people to agree on an ordered list of events. The problem was never being able to form that list (anyone can hash a list of documents, its basic applied crypto.) It was getting a group of strangers to agree on a single result under highly adversarial conditions.
See also: http://unenumerated.blogspot.com.au/2017/02/money-blockchain...
This has nothing to do with blockchains. What you're describing is proof of work with a payout system, and you could implement that without a blockchain at all.
>So while it is true that a blockchain can exist without any kind of currency
It has always been true. This was, in fact, exclusively the case before the first cryptocurrencies - blockchains are data structures, not a concept exclusive to currency.
>Your other point is that a blockchain is simply a linked chain of documents. This is incorrect.
It is exactly correct. The use of blockchains in cryptocurrencies is irrelevant to what they are. If I build the next great money machine tomorrow using a doubly-linked list, it doesn't change what a doubly-linked list fundamentally is. The fact that many people have been introduced to the idea of a blockchain through cryptocurrencies doesn't alter the basic facts.
>The whole point behind a blockchain is that it serves as a way to get people to agree on an ordered list of events.
This is not what the blockchain does. The blockchain helps to ensure that Proof of Work is effective for maintaining consensus after blocks are made - it's the role of PoW to produce the agreement. A blockchain without PoW would allow members to produce new combinations of blocks at will to edit the history.
What are you talking about? The term "blockchain" didn't even exist before Bitcoin. This seems like a case of trying to rewrite history...
Like I said: you can't just abstract this part away as a "data structure" and still have it mean anything. Without proof-of-work your toy example is literally just a made-up document sitting on a single computer.
>blockchains are data structures, not a concept exclusive to currency.
Blockchains as a linked list of hashes don't make sense. You need proof-of-work to decide on the chain. Proof-of-work is expensive so without the currency, proof-of-work doesn't make sense. There are other ways to agree on the order of events but they are not blockchains as understood by the experts in this space (and removing any one of these things undermines the benefits.)
Journalists and enterprise "blockchains" enthusiasts are free to use the term however they like but it doesn't change the fact that blockchains were introduced as an incentivized, trust-free ledger of value -- and by removing any one of its parts the benefits are still lost.
>This is not what the blockchain does. The blockchain helps to ensure that Proof of Work is effective for maintaining consensus after blocks are made - it's the role of PoW to produce the agreement. A blockchain without PoW would allow members to produce new combinations of blocks at will to edit the history.
Blockchains use proof-of-work to create agreement and pay anonymous contributors for doing the work to do so, its as simple as that. A "blockchain" without either of these things is not a blockchain. Incentives are needed to improve social scalability and ensure that there is a reason to continue to secure the ledger.
Proof-of-work is used to give the chain its meaning. I could hash a list of documents right now that said I had millions of dollars but this list couldn't be used by anyone else in an untrusting network of computers without a consensus algorithm... It just so happens that proof-of-work is still the most secure way to do that consensus. So you cannot abstract it away as a "data structure" independent from proof-of-work and the incentives that drive it...
The argument you're trying to make about "blockchains" is something I've only seen enterprise blockchain enthusiasts make about ledgers, and these people usually don't understand the system very well so they end up taking parts of the blockchain away and building something that makes little sense in the end (sometimes its an improvement but usually not.)
What you're describing is a cryptocurrency, or some other form of cryptographically assured distributed ledger with a proof of work.
If you think I'm wrong, look in the original Bitcoin paper and search for "blockchain".
It's justified since blockchain on its own is a relatively simple data structure which on itself is not that significant. It's the composition of all the elements that have given the value and recognition to this technology.
You might want to keep track of the blocks as you create them, or you will find it hard to verify the integrity of a block.
(Do I know the hash of the previous block? Do I know about the next block, if it is not the last block?)
the thing i really want to try making is take a sinatra/redis/crud app and rebuild the database as a distributed database on a blockchain. or at least i think thats what i want to do.
But me, I'm not planning on starting a coin, although I'm pretty interested in the tech behind it, albeit not enough to deep dive into the white papers and code, at least not yet. So I thought this was a nice byte-size chunk and was informative.