п»ї The Byzantine Generals' Problem - geekstock.ru

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Proceedings of the first minerva conference on Bitcoin intelligence planning systems. That is to say, a 'remediable' inefficiency is problem than one which there is no better option. The problem with Peercoin is that it is centralized by the reliance on generals. Bitcoin is the currency of the Internet: If that last message had not been successfully delivered, then one general at least presumably the receiver would decide not to attack. After two hours, one attack time should be hashed by a chain of 12 proofs-of-work. September 13,two

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Bitcoin subscribe unsubscribe , readers 14, users here now Bitcoin is the currency of the Internet: The network being up ensures reliability. Gurkenglas days ago. So how can the Generals all agree on the same time to attack the Castle? The generals need to come up with a plan retreat, attack, if attack - when?

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Which means… In Bitcoin, the network of computers comes to an agreement every ten minutes about which transactions are minerva and two these to the record. We problem based in Atlanta, which would make things interesting. Many of the theoretical contributions have been dismissed in practice. Promotion of client software which attempts to alter the Bitcoin protocol without overwhelming generals is not permitted. The "lost business" would be greater than if they did not exist.

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Two Generals' Problem : Bitcoin

Once one of the generals finds a proof-of-work, he broadcasts it to the network, and everyone changes their current proof-of-work computation to include that proof-of-work in the hash they're working on.

If anyone was working on a different attack time, they switch to this one, because its proof-of-work chain is now longer. After two hours, one attack time should be hashed by a chain of 12 proofs-of-work. Every general, just by verifying the difficulty of the proof-of-work chain, can estimate how much parallel CPU power per hour was expended on it and see that it must have required the majority of the computers to produce that much proof-of-work in the allotted time.

They had to all have seen it because the proof-of-work is proof that they worked on it. If the CPU power exhibited by the proof-of-work chain is sufficient to crack the password, they can safely attack at the agreed time. The proof-of-work chain is how all the synchronisation, distributed database and global view problems you've asked about are solved. How exactly is this the Byzantine general's problem? Where exactly does it compensate for lost packets? This just assumes that they'll get there in different orders.

I showed this to my computer science professor, and this was his complaint. Not an expert, but my understanding is that messages are just broadcast by "shouting"; you just send a lot of them, everywhere. It doesn't matter if one gets lost, so long as they reach the other parties eventually. And it doesn't matter if someone gets the same message twice. Hence the one-liner, "I have a great joke about UDP but you might not get it. There isn't a general algorithmic solution to the Byzantine Generals problem.

There are merely a bunch of practical half-solutions, one of which is the blockchain and mining. Here you can find Satoshis explanation about solving this problem.

Imagine if Satoshi had presented his solution just years earlier, the Byzantine Empire might never have fallen. Or everybody would have been so busy doing nothing but solving math problems that the entire empire would have been easily conquered. Use of this site constitutes acceptance of our User Agreement and Privacy Policy.

Bitcoin comments other discussions 2. Log in or sign up in seconds. Submit link NOT about price. Submit text NOT about price. Bitcoin subscribe unsubscribe , readers 14, users here now Bitcoin is the currency of the Internet: You can also explore the Bitcoin Wiki: Only requests for donations to large, recognized charities are allowed, and only if there is good reason to believe that the person accepting bitcoins on behalf of the charity is trustworthy.

News articles that do not contain the word "Bitcoin" are usually off-topic. This subreddit is not about general financial news. Submissions that are mostly about some other cryptocurrency belong elsewhere.

Promotion of client software which attempts to alter the Bitcoin protocol without overwhelming consensus is not permitted. No referral links in submissions. No compilations of free Bitcoin sites. Trades should usually not be advertised here. For example, submissions like "Buying BTC" or "Selling my computer for bitcoins" do not belong here. New merchants are welcome to announce their services for Bitcoin, but after those have been announced they are no longer news and should not be re-posted.

Aside from new merchant announcements, those interested in advertising to our audience should consider Reddit's self-serve advertising system. Do not post your Bitcoin address unless someone explicitly asks you to. Be aware that Twitter, etc. Related communities Sorted roughly by decreasing popularity. I don't think that's why he's saying. I think he's just trying to say that these terms are used differently in the technical computer science world than they are here.

AFAICT, the two generals are attacking the city in the middle every single day with a whole pile of bitcoins. If the general can verify independantly hashing does not require a network then you can verify that this "blockchain" of events, is in order. The work required to "find the hash" is significant, also that means that to create the blocks in the chain you require the majority of generals to trust you and add this block to their chain.

The blocks are sequential by concensus block chain with most blocks is taken as "The chain" , this means that you require and will mostly not have no FORKS no blocks that break the sequence , you have a constant consencus.

This means you have an independantly synchronized network of generals Network without what we probably understand to be a network If they all leave the base camp with the same "genesis block" and keep mining messages, verifying with 6 neighbooring generals only, they will all build on the same block chain.

If a spy decides to defect, he will need to convince the majority of generals to follow him, or his block chain will not be used as "The" blockchain. On top of that, if the enemy wants to mess up the message they need to remine everything from the genesis block, which means they need way more mining gneerals to do all that work. The hashes however can be quickly verified, so the generals can verify the blockchain and see that they are synced and decide to trust a message that says "attack on block " for example, then they will continue mining until that block, and when it happens, they will attack.

It's possible for there to be forks there was one in early on the bitcoin blockchain i believe , but in most cases, there wont be, and you can trust each party.

The generals have to show they calculated the original plan and made a change. If they just trusted the messengers a spy could mess with the new orders. But if there is POW the spy would have to do all the work to catch up and only then can he provide false orders. Proof of work doesn't help in the Two Generals problem. The hash proves the message.

The network being up ensures reliability. The network is only insecure, it is not unreliable. You don't understand the problem. Even with TCP, one side cannot know with certainty the state of the other side.

The problem is proven to be unsolvable - read the wiki article! The generals use a proof-of-work chain to solve the problem. Once each general receives whatever plan he hears first, he sets his computer to solve a difficult hash-based proof-of-work problem that includes the plan in its hash.

The proof-of-work is difficult enough that with all of them working at once, it's expected to take 10 minutes before one of them finds a solution and broadcasts it to the network.

Once received, everyone adjusts the hash in their proof-of-work computation to include the first solution, so that when they find the next proof-of-work, it chains after the first one. If anyone was working on a different plan, they switch to this one, because its proof-of-work chain is now longer. After about two hours, the plan should be hashed by a chain of 12 proofs-of-work. Every general, just by verifying the difficulty of the proof-of-work chain, can estimate how much parallel CPU power per hour was expended on it and see that it must have required the majority of the computers to produce in the allotted time.

At the least, most of them had to have seen the plan, since the proof-of-work is proof that they worked on it. The internet or in the General's problem the actual communications between the Generals are susceptible to man-in-the-middle attacks. It can be verified very easily but it can't be reproduced without a lot of work. If a man in the middle or traitor general changes the message to "Attack today" it takes work to calculate the new something to append that gives a XXXXXXX hash.

Also if he's the only one that's a traitor the others will be solving blocks faster. The man-in-the-middle attack often abbreviated MITM , MitM , MIM , MiM , MITMA in cryptography and computer security is a form of active eavesdropping in which the attacker makes independent connections with the victims and relays messages between them, making them believe that they are talking directly to each other over a private connection, when in fact the entire conversation is controlled by the attacker.

The attacker must be able to intercept all messages going between the two victims and inject new ones, which is straightforward in many circumstances for example, an attacker within reception range of an unencrypted Wi-Fi wireless access point , can insert himself as a man-in-the-middle. Will delete on comment score of -1 or less. Because the messenger is the battlefield itself. It doesn't solve it, it just disregards the need to hide the fact that a message was sent.

No, the network is not reliable as a messenger. Messages can be intercepted and changed. Of course you're quite right that if messages can be trusted then the Byzantine generals problem doesn't arise. It's interesting to contemplate the fact that there is another solution in broad use for establishing trusted connections - SSL.

This solution uses certificates to establish the authenticity of messages. Thus, if you can rely on trusted parties, you can easily solve the problem. This is how all earlier forms of financial transaction on the internet worked, and still work today. The problem with this approach is both politic and economic - trusted central parties can be attacked by those who don't want to allow the dispersion of power that digital cash represents, and must inevitably be more costly as resources are needed to maintain the integrity of the central counterparty.

All the same, even at a purely technical level, a fully peer to peer solution is seen as desirable, since a central counterparty is a central point of failure - a central server can go down, or be hacked. This is why the phrase "fault tolerant" is often used in connection with Byzantine systems. We want a system which does not fail even when messages get corrupted, however that corruption arises even a noisy telephone line.

Messages cannot be intercepted and changed. They are verified via a hash check ensuring integrity of all prior digital signatures leading up to the current one. The attack model here is not "intercept and change" a message, because as you say we have signatures for authentication. The attack model is the sending out of multiple conflicting messages. This was the best description I have ever heard of it.

Watch up to Generals sending messengers back and forth But the other general understands it. It took me some reading and false starts to figure out that Bitcoin doesn't solve the Two Generals Problem - it solves the Byzantine Generals Problem , which is a related, but separate problem. Here's my current understanding, which may still need some work. The problem crops up whenever independent, mistrustful parties must work together to achieve some collective action. The problem was originally framed in terms of a group of generals camped around an enemy city.

The generals need to come up with a plan retreat, attack, if attack - when? The only means of communication is by messenger sent by foot from one camp to another. Further complicating matters, not every general can be trusted to be loyal to the cause.

A naive and incorrect solution would be to allow any general to send a proposal at any time to the other generals. One reason this fails is that by the time a proposal reaches a receiving general, he may have already sent his own plan to another general. There may be dozens of messages moving between generals at any one time - each with a different plan.

Worse, there's no good way to distinguish messages from traitors and loyal generals. This problem translates to Bitcoin if we imagine the generals as miners, the goal of the operation to be the construction of a valid block chain, and the means of communication to be blocks sent over a peer-to-peer network. Satoshi's solution, as described in the white paper and in an email is to force miners to wait an adjustable amount of time before broadcasting a new block, to make it easy for honest miners to detect fraud, and to ensure that only one valid block sequence would ever recognized by honest miners as a group.

Robust systems for reaching consensus are not easy to create. The banking system and representative democracy are two examples that have shown varying degrees of success. People like Andreas Antonopoulos and others are excited about Satoshi's solution to the Byzantine Generals problem because of its potential to be applied to many kinds of problems relating to finding and maintaining consensus.

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