145

Here is an extremely simplified sketch of the problem, but it should give a pretty good idea of what the problem is. The data: This is the hash of the lastest block (shortened to 30 characters): 00000000000001adf44c7d69767585 These are the hashes of a few valid transactions waiting for inclusion (shortened). 5572eca4dd4 db7d0c0b845 And this the hash ...


62

The following is a description of the global, statistical gamble which is played every 10 or so minutes. The interval of the game is controlled by the difficulty which says how many "hashes" are needed per interval. In other words, the difficulty and target define the "odds of the house" against your chance of getting a winning SHA hash. The nonce is the ...


38

They try to find a random nonce (a little random data) that goes into a block and makes the block have a (SHA256) hash that (in binary) starts with a certain amount of 0's. The more zeroes the more rare hash is. A good hash' outcome is not predictable, and so you have to try a lot of times to find a good nonce. The amount of zeroes are based on how ...


37

The Mining Algorithm is as follows: Step 0 - Retrieve the hash of the previous block from the network. Step 1 - Gather a list of potential transactions known as a "block". This list of transactions comes from the peer-to-peer bitcoin network. Step 2 - Calculate a hash for a block of potential transactions along with a random number. Step 3 - If the hash is ...


24

In Nextcoin, proof of stake is used. So the "mining" process there is just about holding coins and leaving your computer on. It doesn't involve powerful CPUs. Each block (every 60 seconds), a random Nextcoin is selected to be the next "miner". There are 1 billion coins so the odds of a single wallet being selected is the number of Nxt in that wallet ...


21

Proof of stake is a proposed alternative to proof of work designed to increase network security. It's not currently implemented in the main chain (and would likely require a hard fork to implement), but alt currency PPCoin features a hybrid proof-of-stake/proof-of-work system of sorts. With proof of work, the likelihood of mining a block is dependent on the ...


19

The big advantage on the Bitcoin side is that its technology is now well-proven. Ripple's consensus system is the newcomer. Ripple was designed by people who had the benefit of seeing exactly what Bitcoin was doing and its strengths and weaknesses. Ripple's consensus process can validate a transaction such that irreversibility is reasonably assured much ...


18

The specific reason that AMD cards are more efficient for Bitcoin mining is twofold and the answer to this question depends on both reasons: AMD GPUs tend to have lower-end ALUs but make up for this by packing more ALUs onto the card overall. For most hash algorithms this is preferable. AMD GPUs uses ALUs which can perform the 32-bit integer right rotate ...


18

Solving SHA256 hash problems on Bitcoin is useful in the sense that secures the Bitcoin blockchain, but if your question is: "why can't it do something computationally useful as a side-effect?", then I think the answer is "we don't know how". For Bitcoin to work, the proof-of-work that miners do must have the following properties: Easy to verify solutions ...


18

Forget PoW for a second: lets instead imagine that you have a box, and you've placed a lock on it, in order to secure it's contents. Now, if someone asks you how secure the contents are, then the size and type of lock is fairly important. Tying the box closed with a bit of string isn't very good security, at least compared to a heavy-duty padlock. For an ...


17

NooShare is an idea for: a decentralised ledger similar to Bitcoin with the novel feature that its proofs of work are iterations of essentially arbitrary Markov-Chain Monte-Carlo (MCMC) chains, the scheduling of which can be purchased using the currency itself. It is a novel economic basis for sharing fallow computational resources. I don't know ...


15

The scrypt() algorithm has at its core a routine called ROMmix. Basically, it defines V(1) = hash(message) V(2) = hash(hash(message)) V(3) = hash(hash(hash(message))) ... and it calculates V(V(V(V(...(message)))) Since computing V(n+1) requires computing V(n) first, the most efficient way to do this is to cache all of the previously-computed ...


12

Mining provides a way to reach consensus on what the transaction ledger should look like and know that nobody is cheating. That's the non-technical definition of mining. What exactly is Mining? The "authority" for double spending is the blockchain. The blockchain consists of the history of all blocks in the blockchain plus the next block of transactions. ...


11

Bitcoin miners find a random number (called a "Nonce") that when inserted into the current block makes the hash be below the current target. They then send that current block around the network and everyone checks their work (the proof-of-work) by hashing the block and checking if the result is below the current target. In mining pools, miners do the same ...


11

As you mentioned, bringing coins into the network is one of the main purposes of mining. But this reward is just an incentive to do the other more important part of mining: 'processing' transactions. Immutability As detailed here, when a block has been solved, not a single bit can be changed without invalidating it. This means that all of the ...


10

No, mining will not come to an end at that point. The article is incorrect. Mining will continue once the block rewards are no longer available, as transaction fees will continue to be offered. As the block rewards tend towards zero, the total value of transaction fees in each block will start to exceed the block reward. This will happen long before the ...


10

The important thing here is, that every mining pool/solo miner is working on a different input: They have different coinbase transactions and are working on different sets of transactions. Further entropy can be added by changing the nonce and extra-nonce, by adding another transaction, or by changing the order of the transactions. While there can be block ...


10

The time between consecutive blocks follows the exponential distribution, with mean (roughly) 10 minutes. This means that the variance is 100 minutes^2.


10

I don't know of any such list yet, but no reason we can't start making one. :) Others should feel free to add their findings via an edit. Proof of Work Proof of Stake Proof of Activity Proof of Storage Proof of Knowledge Proof of Stake Velocity Proof of Burn Dual Purpose Proof of Work (Primecoin) Proof of Lock (Tendermint) Delegated Proof of Stake (...


10

Imagine I have 1 bitcoin. And imagine I can form a transaction to send that bitcoin to Alice or I can form a transaction to send that bitcoin to Charlie. Now, what stops me from forming both transactions? Nothing. So, if I do that, how will people know which transaction is valid? Clearly, without some reliable way to tell which of those two transactions ...


10

Because each miner may select the transactions (and the order in which they are included) in each block. Also, they do not all start on the same exact nonce, in fact they are changing more than just the nonce in many cases (e.g. block versions - see ASIC BOOST). This means that they are not all performing the HASH256 (proof of work algorithm) on the exact ...


9

The simple answer: no. The not to simple answer: extremely unlikely. Miners hash an input block, in the hopes of getting a result that satisfies the difficulty requirement, i.e., has a certain number of zeroes in front. Now the possibilities for the miner to vary the input are quite large. There is the 4 byte nonce, there is the order transactions are put ...


9

For Peercoin specifically, PoW and PoS blocks are independent. Just as you're betting your consumed electricity and CPU-time vs. the possible PoW-blok's reward, in the PoS blocks you're betting your coin-age: the amount oF PPC you own multiplied by the number of days they've sitted idly at your wallet. It must be a minimum of 30 and a maximum of 90 days for ...


9

Well, I know of one altcoin that does useful work: Primecoin. As Wikipedia describes it: Primecoin (sign: Ψ; code: XPM) is a peer-to-peer open source cryptocurrency that implements a scientific computing proof-of-work system. Primecoin's proof-of-work system searches for chains of prime numbers. Primecoin already has quite some world-record prime chains ...


9

Nothing directly prevents it in Bitcoin, and indeed the attack has been demonstrated on testnet3 many times---it's the primary reason that testnet3 currently has almost three times as many blocks as Bitcoin, despite being launched several years after Bitcoin mainnet and with a something similar to[1] Bitcoin's 10-minute average block interval. Indirectly, ...


9

There are multiple definitions of the term "double spending" at play here. First, there is the actual definition of double spending: to spend the same money multiple times. A simple example of this is the coin on a string in a vending machine. You put tie a string to a coin, when you put the coin in the machine, it thinks you paid, you get whatever you want ...


9

Proof of work does not create trust. It creates incentive. Miners are paid if their block is eventually part of the main version of history ("blockchain") that the network accepts. They must irrecoverably burn electricity in order to create blocks, which costs them money; money they only get paid for if their block "wins". These factors together mean that ...


8

Assume for a second that we found a proof of work algorithm that had all of the good properties of sha256, but was also useful for SETI and maintaining world peace. Now suppose a group of miners collectively have more than 51% of the hashing power. In which of the following scenarios are they more likely to collude to double spend via a 51% attack: A) When ...


8

Some discussions around how to make it more useful https://en.bitcoin.it/wiki/Intrinsic_worth_brainstorming https://bitcointalk.org/index.php?topic=11834.0


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