In previous posts, I gave an explanation of the cryptographic building blocks of Bitcoin. Now I'll give a more "big picture" overview of how the overall system works. As before, I expect this to be easier to follow than the explanations I had to read to get to my current level of understanding.
Let's start from the general problems that a decentralized, anonymous (or pseudonymous) currency system has to solve. The most fundamental problem, is that of achieving "common knowledge" of the currency ownership. Specifically, everyone has to know not only who is the valid owner of any currency unit (so as to prevent double-spends); they must also know that everyone else knows the same answer. And they must know that you know that they know (and so on) this information. (This level of knowledge is known in the literature as common knowledge, but with the definition I just gave, not the conventional one.)
In other words, it's not enough that I know the current ownership status of any coin; I must count on others agreeing with me and knowing I agree with them. If you could accomplish this, you could get everyone to use and depend on the same record, thereby resolving disagreements about who is the current owner of what -- without trusting any one person. It is this problem that required the "key" innovation behind Bitcoin, as it has normally needed a trusted authority to solve it.
So what is this key innovation to solving that problem? The first insight is that it's possible to prove how many computing cycles were spent working on something. And with a system that implements such a "proof protocol", you can have a transaction record that provably has a certain number of past computing cycles spent on it. Then, you just need most of the users of a system to agree that they'll "go along with" whatever transaction record has the most computing cycles spent on it. Then, you know what the "real" global ledger is -- and you can trust that everyone else is using it too! (And they can trust that you're using it, etc.)
And there you have it: proof of ownership, without a central authority.
With that problem and solution in mind, a lot of the complexity of Bitcoin starts to make sense.
Remember how I had previously mentioned that bitcoins are initially doled out based on who can solve complex mathematical problem? Well, that math problem doesn't just exist to get initial bitcoins widely distributed -- that's not even the most important function of the problem. The main purpose, rather, is to prove that the the largest number of computer cycles were spent on a given transaction record. You see, if you start from the last known solution (which itself has the transaction record up to a point in time), you are starting from a record with, so far, the biggest number of cycles spent on it. (And the Bitcoin protocol specifies that you should start from the biggest one, though its in your own interest, as you will see.)
If you publish an "update" -- the previous ledger plus more recent transaction -- with the next solution, then the other users know that your purported ledger has all the cycles you spent on it plus all the cumulative cycles spent up to the last solution. Therefore, if you want to claim credit for the latest solution (entitling you to the 50 BTC bounty), you should start from the ledger in the latest solution.
So, let's step back and summarize. Here is a simplified version of what goes on in the Bitcoin network:
1) Whenever users want to transfer their bitcoins over to someone else, they broadcast a message describing the transfer and sign it with their private key.
2) Whenever a user receives a message indicating a transfer, they first check that the signature is valid (see previous post on digital signatures), and that the address doesn't spend more than the latest "confirmed" ledger shows it as having. If it checks out, they keep the message and propagate it to others.
3) All users wishing to claim the reward for a solution (aka "miners") bundle up all transactions they know of (i.e., new ones plus those in the latest confirmed ledger), and convert it into a math problem unique to that transaction set. They then work on solving that problem.
4) When someone finds a solution, they broadcast it, with their bundle of known transactions (new latest ledger), to all other users. Like with individual transactions, anyone who receives one of these checks it, and if valid, broadcasts it to others.
5) Miners who receive a new valid solution quit their current search for a solution, then take the latest ledger as definitive. Again, as in 3), they bundle up new transactions they hear of, add them to this new ledger, and try to solve a new math problem unique to the new transaction set, and the process begins anew.
In practice, sometimes different users will simultaneously find a solution, or solutions will propagate through different parts of the network at different speed. So miners will typically hold on to the 4-5 last latest ledgers, in case one of them is extended and becomes definitive. Users, for their part, will wait for several new ledger solutions before accepting their transaction is firmly in the network.
Oh, and as for the relevant jargon? A new solution, with its bundle of old and new transactions, is called a block. The complete transaction record, with each solution along the way, showing how the build off of each other, is called the block chain -- because each block "chains" off a previous ledger.
Now, I'm leaving out a lot of details, but I hope that explains the overall system and the different roles played. In the future, I'll go into more detail on:
- How you prove you spent X computing cycles on something.
- How you prevent situations where miners constantly find solutions at the same time.
- How you minimize storage requirements for the transaction record.
- How overlapping solutions get resolved.
- And much more.
A blog by Silas Barta
Showing posts with label property rights. Show all posts
Showing posts with label property rights. Show all posts
Saturday, July 16, 2011
Thursday, May 21, 2009
Fun with graphics and the environment!
Well, the Environmental Defense Fund has a cute graphic out (HT: Free Advice) promoting "green jobs":
The basic idea, as you probably figured out from the graphic, is that mandating pollution caps will give people something to do, thus reducing unemployment. They don't put it that way, of course, but that's the idea, and it's a rehash of the Broken Windows Fallacy.
This justification for pollution restrictions misses the point, of course. Assigning well-defined, sustainable pollution rights is a good idea, for the same reason that assigning rights to any scarce resource is a good idea: because of justice and efficiency, not because it would add another task for people to do.
In light of all of that, I decided to pull a SomethingAwful and put different words into the graphic, in an attempt to criticize my nemesis Bob Murphy's (of the Free Advice site linked above) sudden love of Coasean extortion payments when it comes to pollution. Enjoy!
The basic idea, as you probably figured out from the graphic, is that mandating pollution caps will give people something to do, thus reducing unemployment. They don't put it that way, of course, but that's the idea, and it's a rehash of the Broken Windows Fallacy.
This justification for pollution restrictions misses the point, of course. Assigning well-defined, sustainable pollution rights is a good idea, for the same reason that assigning rights to any scarce resource is a good idea: because of justice and efficiency, not because it would add another task for people to do.
In light of all of that, I decided to pull a SomethingAwful and put different words into the graphic, in an attempt to criticize my nemesis Bob Murphy's (of the Free Advice site linked above) sudden love of Coasean extortion payments when it comes to pollution. Enjoy!
Tuesday, August 26, 2008
Setting scarcity straight, once and for all
In case you haven't been following, Bob Murphy wrote a shameful op-ed on the proposed Cap-and-Trade scheme, which prompted quite a bit of criticism from me and "TokyoTom" (good summary). If Bob were merely claiming that politicians screw things up, none of us would have objected. Unfortunately, he said a lot more than that. The focus of this post will be on his claim that carbon emission caps "don't reflect scarcity".
Now, as you see in the exchange, Bob tries to claim that what he really meant was that if the carbon cap were too low, or somehow not correct, that wouldn't reflect scarcity, but otherwise it would. If you follow the exchange, you'll see how I showed that there is no possible way, based on the phrasing of his argument, that he could claim the op-ed meant that. Nevertheless, he has repeatedly gotten considerably sympathy from others (not me) with this last-ditch attempt to salvage himself from having to apologize for his op-ed, by arguing that, so long as government doesn't precisely set the cap to what the perfect, pure, austere free market would, the cap still would not reflect scarcity and he was technically correct.[1] I will now show how even this claim is wrong, by starting from a simple case, and working up to the claim Bob made.
Economic scarcity refers to the situation where "not all of society's goals can be pursued at the same time; trade-offs are made of one good against others." Now, let's see where this takes us.
Problem #1: I want to hit Bob. Bob does not want me to hit him. Does scarcity exist?
Answer: Yes, because it's impossible to satisfy the social goals of both me hitting Bob and Bob not being hit by me.
Problem #2: I attempt to hit Bob. Bob retreats to his house and locks himself inside. I attempt to bypass the locks. Does the difficulty of getting to Bob reflect scarcity?
Answer: Yes. Since my goal comes at the cost of Bob's, Bob will take measures to ensure I do not reach mine. The lock, a manifestation of Bob's desire not to be hit, therefore reflects scarcity.
Problem #3: Having such difficulty getting past Bob's locks, I instead try to act out my anger against him by sending 100 locusts down his chimney. I would have sent more, but my insurer restricted me to having only 100 locusts at any given time. Does this restriction on my ability to carry locusts reflect scarcity?
Answer: Yes. In deciding the max it will allow me to carry while maintaining coverage, the insurer must consider how badly I can hurt others with a given number of locusts, since hurting others can cause me to be liable for damage. The limit, being a mechanism by which the conflict with the desires of others not to be hurt manifests, therefore reflects scarcity.
Bonus answer: Note that locusts are not guaranteed to hurt Bob, but the more I send, the more likely that is. So the limit on how many locusts I can have only reduces the harm to Bob in a probabilistic sense. However, the limit still reflects scarcity.
Problem #4: Same situation, but in an alternate universe. There is an intrusive government that passes laws in an attempt to minimize conflict between its subjects and thus maximize its looting; insurers of the type above don't exist. It has decreed that people may own 146 locusts, but no more. In trying to buy more than 146 locusts, a red flag goes up, and I am prevented from buying any more. Does this difficulty in buying locusts reflect scarcity?
Answer: Of course. Whatever criticism of government you might make, its decrees ultimately rule in favor of some goals and against some others. Therefore, when it hinders one goal (such a stopping locust attacks) in preference to another (such as the goals of locust-lovers in keeping collections), this is a manifestation of scarcity.
Problem #5: What if the government's limit were 23 instead? Or 100? Or 0?
Answer: Yes, it still would reflect scarcity. No matter how closely or poorly it approximates what limits would result from market processes, the above reasoning applies.
Problem #6: Scientists reveal that emitting substance X increases the probability of catastrophic damage. The governments of the world then place an overall emission cap of C. As a result of the cap, the price of doing things that result in X emission goes up. Do the higher prices from the cap reflect scarcity?
Answer: Yes, for the same reasons as in #4: the higher prices ultimately result from the (probabilistic) conflict with the goals of others. Yep, even substance X is CO2.
Problem #7: If Bob responded to the above line of reasoning (about scarcity) by saying that the proposed scheme is not a Blicknorg [2], is that responsive?
Answer: Don't be ridiculous; that's just changing the topic.
Long story short, the caps do reflect scarcity.
[1] And how would you ever learn what cap a free market would set? Why, you first have to price all resources, including and especially the atmosphere. Anyone want to take a wild, wild guess as to the ratio of the words that Bob has spent:
a) advocating that atmospheric property rights be clearly delineated,
to the words Bob has spent
b) demanding that government NEVER do a SINGLE thing to in any way define such rights?
I'll give you a hint: it's somewhere between "zero" and "can I have what you're smoking?"
[2] Actually, in the discussion, what Bob actually tried to do to refute the solid argument that caps would reflect scarcity, was claim that the caps are not a "market solution", rather than a Blicknorg. However, since he refused to ever clarify what exactly that meant, despite being asked several times, he might as well have said Blicknorg.
Now, as you see in the exchange, Bob tries to claim that what he really meant was that if the carbon cap were too low, or somehow not correct, that wouldn't reflect scarcity, but otherwise it would. If you follow the exchange, you'll see how I showed that there is no possible way, based on the phrasing of his argument, that he could claim the op-ed meant that. Nevertheless, he has repeatedly gotten considerably sympathy from others (not me) with this last-ditch attempt to salvage himself from having to apologize for his op-ed, by arguing that, so long as government doesn't precisely set the cap to what the perfect, pure, austere free market would, the cap still would not reflect scarcity and he was technically correct.[1] I will now show how even this claim is wrong, by starting from a simple case, and working up to the claim Bob made.
Economic scarcity refers to the situation where "not all of society's goals can be pursued at the same time; trade-offs are made of one good against others." Now, let's see where this takes us.
Problem #1: I want to hit Bob. Bob does not want me to hit him. Does scarcity exist?
Answer: Yes, because it's impossible to satisfy the social goals of both me hitting Bob and Bob not being hit by me.
Problem #2: I attempt to hit Bob. Bob retreats to his house and locks himself inside. I attempt to bypass the locks. Does the difficulty of getting to Bob reflect scarcity?
Answer: Yes. Since my goal comes at the cost of Bob's, Bob will take measures to ensure I do not reach mine. The lock, a manifestation of Bob's desire not to be hit, therefore reflects scarcity.
Problem #3: Having such difficulty getting past Bob's locks, I instead try to act out my anger against him by sending 100 locusts down his chimney. I would have sent more, but my insurer restricted me to having only 100 locusts at any given time. Does this restriction on my ability to carry locusts reflect scarcity?
Answer: Yes. In deciding the max it will allow me to carry while maintaining coverage, the insurer must consider how badly I can hurt others with a given number of locusts, since hurting others can cause me to be liable for damage. The limit, being a mechanism by which the conflict with the desires of others not to be hurt manifests, therefore reflects scarcity.
Bonus answer: Note that locusts are not guaranteed to hurt Bob, but the more I send, the more likely that is. So the limit on how many locusts I can have only reduces the harm to Bob in a probabilistic sense. However, the limit still reflects scarcity.
Problem #4: Same situation, but in an alternate universe. There is an intrusive government that passes laws in an attempt to minimize conflict between its subjects and thus maximize its looting; insurers of the type above don't exist. It has decreed that people may own 146 locusts, but no more. In trying to buy more than 146 locusts, a red flag goes up, and I am prevented from buying any more. Does this difficulty in buying locusts reflect scarcity?
Answer: Of course. Whatever criticism of government you might make, its decrees ultimately rule in favor of some goals and against some others. Therefore, when it hinders one goal (such a stopping locust attacks) in preference to another (such as the goals of locust-lovers in keeping collections), this is a manifestation of scarcity.
Problem #5: What if the government's limit were 23 instead? Or 100? Or 0?
Answer: Yes, it still would reflect scarcity. No matter how closely or poorly it approximates what limits would result from market processes, the above reasoning applies.
Problem #6: Scientists reveal that emitting substance X increases the probability of catastrophic damage. The governments of the world then place an overall emission cap of C. As a result of the cap, the price of doing things that result in X emission goes up. Do the higher prices from the cap reflect scarcity?
Answer: Yes, for the same reasons as in #4: the higher prices ultimately result from the (probabilistic) conflict with the goals of others. Yep, even substance X is CO2.
Problem #7: If Bob responded to the above line of reasoning (about scarcity) by saying that the proposed scheme is not a Blicknorg [2], is that responsive?
Answer: Don't be ridiculous; that's just changing the topic.
Long story short, the caps do reflect scarcity.
[1] And how would you ever learn what cap a free market would set? Why, you first have to price all resources, including and especially the atmosphere. Anyone want to take a wild, wild guess as to the ratio of the words that Bob has spent:
a) advocating that atmospheric property rights be clearly delineated,
to the words Bob has spent
b) demanding that government NEVER do a SINGLE thing to in any way define such rights?
I'll give you a hint: it's somewhere between "zero" and "can I have what you're smoking?"
[2] Actually, in the discussion, what Bob actually tried to do to refute the solid argument that caps would reflect scarcity, was claim that the caps are not a "market solution", rather than a Blicknorg. However, since he refused to ever clarify what exactly that meant, despite being asked several times, he might as well have said Blicknorg.
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