Are 51% Attacks a Real Threat to Bitcoin?

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Recently over dinner, I was asked to explain bitcoin mining, and I struggled as it is entangled with a number of other concepts. Wait for it to be mined in a block average 10 mins. Miners take the list of unconfirmed transactions specifically, those dave hudson bitcoin charts they know aboutand they bundle them into a block, which is just a list of transactions plus some other data. If they guess right, then the block is published to the rest of the network.

The computers on the network validate that the block meets the criteria, and dave hudson bitcoin charts ignore it or store it into their blockchains. The competition then starts again with the unconfirmed transactions that have accumulated since. The network adjusts the difficulty of the guessing game to target a block being created every 10 mins or so, irrespective of the amount of computing power in the network. Wait for more blocks to be mined on top average 10 mins per block.

The current advice suggests that after 6 blocks, the chances of the transaction being unwound dave hudson bitcoin charts to dave hudson bitcoin charts competing longer chain replacing your blocks is very small. If you are receiving a payment, then the higher the value your payment, the longer you may want to wait to reduce the chance of your payment being unwound.

There are two parts to this. First you need a way to get transactions into the ledger, secondly you need a way to make it expensive for miscreants to add dishonest blocks. Transactions are added to the ledger in blocks so as to create some sort of time order to the transactions.

However, the guessing game makes it computationally expensive therefore financially expensive to add blocks. This cost acts as a deterrent to miscreants who would otherwise want to add their dishonest blocks. When you mine a block, get to collect any voluntary transaction fees from the transactions you have included.

The reward decreases with time, and in theory, transaction fees will replace the block reward. If there are more unconfirmed transactions dave hudson bitcoin charts can fit in a block, rational miners will mine the ones with the highest transaction fees first.

A hash is a fingerprint of data. Hashes look random compared with the data put in. You can play with hashing here: If you change just one part of the data, the hash looks entirely dave hudson bitcoin charts. I added a question mark:. Adding or changing just one characters results in a totally different-looking hash. What does the hash dave hudson bitcoin charts this look like?

I kept going, and to find something that gave a hash starting with a double zero, it took attempts:. Bitcoin mining is essentially the same game, where you tweak the input data the block header so that you get an output hash that matches what is required by the network at that point in time.

Satoshi Nakamoto, the proposer of bitcoin, recognised that if dave hudson bitcoin charts want lots of people to spend hardware and energy creating this network, you need to incentivise them: The white paper is hereand well worth dave hudson bitcoin charts read.

How do you pay anonymous participants, without creating some sort of power structure? Any source of funding provided by some entity e. Satoshi realised that an intrinsic source of funding, where a payment is paid by the system rather than by any external party, would be the answer.

This is why miners are paid by the system, in tokens which have a value that is related to the size and security of the system. Theoretically, the more valuable the tokens become, the more money can be spent mining, leading to an increase in security and an increase in the value of the network. You just need to download some software and run it.

Your computer will then start taking transactions that it receives through the bitcoin network, and it will bundle them into blocks, and start mining the block.

Your chance of mining a block is somewhat proportional to the amount of computing power you throw at it, because mining is a guessing game, and faster computers guess more quickly. In practice, successful miners form groups, dave hudson bitcoin charts pools, and combine their processing power. If they win a block, the reward gets shared between participants.

This is similar to forming a lottery syndicate, so you win less, but more often, and your income becomes lumpy. So despite the rhetoric of bitcoin being decentralised, it is controlled by a handful of people in China.

See this Financial Times article for further reading: Mining is mainly done by Chinese pools. Inat first people could mine successfully on their laptops and home computers, using the CPU Central Processing Unit to do the calculations. This was the next revolution in hashing power, starting in I recommend this article which describes the history of mining better than I can: Other nodes will reject this, which is why it is important to confirm a transaction across a number of nodes.

With transactions, the effect a dishonest can have is very limited. If the rest of the network is honest, they will reject any invalid transactions coming from the baddie, and they will hear about valid transactions from other honest nodes, even if the miscreant is refusing to pass them on.

Dave hudson bitcoin charts blocks, if the miscreant has sufficient block creation power and this is dave hudson bitcoin charts it all hinges onhe can delay your transaction by refusing to include it in his blocks. This lets him unwind a transaction. To conclude, bitcoin mining is the theoretically decentralised process where anyone can add a block of transactions to the bitcoin blockchain, without needing permission from any authority, and get paid in bitcoins for it.

It is made deliberately difficult, using proof of work as a defence against Sybil attacks. These articles are helping me a lot in understanding bitcoins and blockchain. Many thanks for all the useful, helpful information you have in this article, and across the site.

Hi Sean, yes you can mine for any amount less than the limit and it seems to have been done before. You are commenting using your WordPress. You are commenting using your Twitter account. You are commenting using your Facebook account.

Notify me of new comments via email. How to double spend. Thanx for your work. Absolutely brilliant series of articles — many thanks! Can someone be outside of a pool and mine for rewards smaller than Leave a Reply Cancel reply Enter your comment here Fill in your details below or click an icon to log in: Email required Address never made public.

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Most participants in the ongoing Bitcoin block size debates have a point of agreement; that a shortage of block space should have an effect on transaction fees. Arguments aside, then, let's see what has actually been happening. Are fees going through the roof? Are miners going to be celebrating a potential offset to the block reward halving that looms in July ?

The results seem a little surprising! Bitcoin miners earn their per-block rewards in two ways. They collect a block reward subsidy that halves every , blocks and they collect the fees assigned each transaction within a block. Historically the fees have represented a tiny fraction of the total reward. Despite being far smaller, they are still actually worth a reasonable amount of money per year to the block makers who collect them.

If capacity is scarce within the Bitcoin blockchain we would expect to see transaction fees rise dramatically as users seek to ensure their transactions are processed ahead of everyone else's, but are there any strong indications that this has happened? We can see that throughout the BTC-denominated average fee per transaction steadily declined, stabilized in the first half of and then jumped in July Thereafter the average fee actually started to fall again.

Transaction fees have bounced back up a little in the first few weeks of , but this doesn't appear to be the fee armageddon that was forecast! If anything fee levels are now back where they were in early As we'd expect, the transaction volume has been steadily increasing otherwise there would be no block size bickering.

The last 2 months have seen particular jumps, but that may in part be explained by the dramatic increases in hash rates again. Rather than a nominal 10 minute block time we've been seeing nearer to 9 so the available capacity for low-fee or zero-fee transactions has been higher than we'd expect.

Instead of 6 MBytes per hour we've probably had more like 6. It's quite odd that the transaction rates have jumped quite so much in the last 7 months though, almost doubling. This is the very same period in which the average per-transaction fee had jumped up.

The spike in July gives some indication of what happened, however, as this corresponds to the first "Bitcoin flood attack" see: The flooding event caused the network to adjust fees upwards, but thereafter fees steadily declined again as fee-bearing transactions saw minimal impact on confirmation times. This one actually looks worse.

It appears that the fee levels have steadily been increasing since July , but we're seeing the effect of two different things. It's notable though that they're still lower than they were in the first 9 months of If we look at the cost of each transaction as measured by the USD-valued total mining rewards for each day and the numbers of transactions per day we see that things have been incredibly stable for the last 12 months:. Far from a fee market emerging to inflate transaction costs, we don't appear to have very much evidence of anything dramatic happening yet.

There are a number of possibilities, but one is that the transaction volume doesn't really reflect transactions that most users care about. Low value fees for unimportant transactions may well be leaving more interesting transactions unaffected by any concerns about capacity. While the block size squabbles will continue it's unclear that there have yet been any wide-scale implications for current users of the network.