Questions tagged [blockchain]

This tag should be used for questions pertaining to the blockchain. The blockchain is a list of all transactions that have occurred using the Bitcoin currency. It consists of blocks which are linked to each other, and each block consists of transactions. DON'T USE THIS FOR THE SERVICE NAMED 'blockchain.info'!

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80 votes
7 answers
87k views

Can I download the whole block chain from somewhere?

Every time I turn on the Bitcoin client it takes days to catch up with the block chain. Are there alternatives to getting it trickling through the peer-to-peer network? Can I just download it ...
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69 votes
2 answers
95k views

Can someone explain how the Bitcoin Blockchain works?

I'm trying to figure out how the blockchain works and how to read it via blockchain.info website. Is there a laymen way of explaining how the block chain works and how to read the blockchain to trace ...
64 votes
9 answers
35k views

How anonymous are Bitcoin transactions?

I read some sources that say Bitcoin transactions are anonymous, some that say they are semi-anonymous, and some that say they are not anonymous at all. In what ways are the transactions anonymous ...
61 votes
6 answers
66k views

What is the Merkle root?

The Bitcoin wiki Vocabulary article explains why the Merkle root exists: Every transaction has a hash associated with it. In a block, all of the transaction hashes in the block are themselves ...
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48 votes
3 answers
41k views

How can I run bitcoind in pruning mode?

I read this comment: You could consider running a pruning node, which is practically the same as a full node (including security), except it throws away some of the old history. Version 0.11 ...
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47 votes
8 answers
107k views

Where are the user's bitcoins actually stored?

On the person's computer? On bitcoin.org? :) Where does that information reside that tells others and me how much bitcoins I have? I assume it can't be on my PC because I could easily hack the file ...
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45 votes
4 answers
78k views

How do I see the IP address of a bitcoin transaction?

How do I see the IP address that someone used to send or receive bitcoins with? Is it stored in the blockchain?
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44 votes
1 answer
9k views

What do the different .dat files contain?

What data do different Bitcoin .dat files contain? How about the other files in the same folder? The wallet.dat file is somewhat documented and there are some ways to convert it to human-readable ...
  • 42.8k
39 votes
4 answers
16k views

What are the keys used in the blockchain levelDB (ie what are the key:value pairs)?

I am wondering if I can use node.js and levelup to access a copy of the blockchain database directly. But from what I can see, I need to know the name of the key(s) before I can get any data, as this ...
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39 votes
3 answers
12k views

What are checkpoints?

I often read that checkpoints protect the network from a 51% attack because an attacker cannot reverse transactions made before the last checkpoint. How exactly does this checkpoint mechanism work? ...
  • 11.5k
38 votes
10 answers
36k views

How to check if the block chain is up to date using bitcoind or json-rpc?

I read the full api method list and did not seem to find one. I suppose there is no command specifically for that purpose, so what is the general way of doing this? I would consider checking the ...
  • 11.4k
37 votes
10 answers
29k views

How is it possible to launder bitcoins?

Some services, such as bitcoinlaundry.com, claim that they can launder your bitcoins. Since all bitcoin transactions are publicly logged, how is this done? Wouldn't it be possible to trace back the ...
  • 11.5k
36 votes
6 answers
9k views

How do I reduce the size of the block chain data on my machine?

The block chain file is getting rather large, ~500MB. Is there a way to trim it or clean up, or maybe configure it to be limited in the future? I am using the stock Bitcoin client on Ubuntu.
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35 votes
5 answers
34k views

How are transactions broadcast to the rest of the network?

If a person sends a transaction to another person, and Bitcoin is a peer-to-peer application, how will the transaction get to the rest of the Bitcoin community? How does everyone have the same ...
34 votes
5 answers
53k views

How to make a new blockchain from scratch

In the same vein as setting up a private DNS root server and using whatever domain names you want, how do you generate your own blockchain and mine your own coins? P.S. I don't want any answers ...
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33 votes
1 answer
12k views

What is the database for?

I see the block chain is stored according to the block chain format specification. But I also see there is a database, which is currently a leveldb database. Why is the block chain stored in two ...
33 votes
7 answers
10k views

Is a private blockchain better in any sense than a database?

Since the banks appear to be currently looking into the idea of "blockchains" but don't want to be dealing with "Bitcoin", it seems that there is a lot of hype for private blockchains out there like ...
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32 votes
9 answers
6k views

Why don't the timestamps in the block chain always increase?

The timestamps starting at block 145044 are: 145044: 2011-09-12 15:46:39 145045: 2011-09-12 16:05:07 145046: 2011-09-12 16:00:05 // ~5 minutes before prior block 145047: 2011-09-12 15:53:36 // ~...
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31 votes
2 answers
10k views

What is the block maturation time?

I was reading the wiki article about the blockchain and I didn't understand the part in bold: When a block becomes an orphan block, all of its valid transactions are re-added to the pool of ...
  • 11.5k
31 votes
3 answers
11k views

How is the whitepaper decoded from the blockchain (Tx with ~1000x m of n multisig outputs)

The whitepaper is apparently encoded at 54e48e5f5c656b26c3bca14a8c95aa583d07ebe84dde3b7dd4a78f4e4186e713, which is an m of n multisig Tx with 947 outputs (just under the scriptsig limit of 20kB!). ...
31 votes
5 answers
4k views

What would happen if a portion of the Bitcoin network was separated from the rest of the network?

Yesterday I asked a question over at SuperUser, so that I could have my facts straight before asking this question. The scenario sets the basis for this question. Regarding bitcoin, what would ...
  • 2,182
30 votes
2 answers
6k views

Are there any studies into the size of the blockchain scaling over time?

After watching some of one of the 28c3 talks, It got me thinking about just how scalable Bitcoin really is. With the size of the blockchain currently, given the number of transactions/users, will the ...
  • 1,750
29 votes
4 answers
33k views

Where do I find the *actual* blockchain size?

Okay, my hard drive is a bit cramped, and the Blockchain for my Bitcoin client is completely sucking up my free space. I want to know how much room I need to be prepared to lose. This isn't a ...
28 votes
2 answers
16k views

What does the term "Longest chain" mean?

What does the term "Longest chain" mean, as there is only one 'right' blockchain exists? How another longer chain would make the 'right' chain invalid?
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27 votes
2 answers
8k views

How many Bitcoin addresses are/have been carrying a balance?

Bitcoin addresses can be generated at will, and the theoretical limit to their number is high. Addresses are constantly being generated to receive funds or balance transactions, but they are also ...
26 votes
4 answers
39k views

What is a double spend?

What is a double spend? As someone who uses Bitcoin, what do I need to know about how the Bitcoin system prevents double spends? Are there still circumstances where they can occur?
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26 votes
2 answers
9k views

When and how did Bitcoin start?

Exactly when was the first block mined and the first bitcoins generated? How many people knew about the project at this point? Had the project been publicly announced before the first block was mined ...
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25 votes
1 answer
14k views

What is a hard fork?

When people talk about possible changes to how Bitcoin works they sometimes say a particular change would require a hard fork. What does that mean? Can a hard fork cause problems?
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24 votes
4 answers
20k views

Is bitcoin mining itself compromising the security of SHA256

Following good scientific practice I propose a Theory/Hypothesis and now ask you to test it. Initially this is a "thought" experiment but may progress to real testing depending on your thoughts. Back ...
22 votes
2 answers
4k views

How does a client decide which is the longest block chain if there is a fork?

Is it only the block height or is it the effort that went into the forks? In other words: does this decision account for different difficulties?
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22 votes
1 answer
10k views

How does Bitcoin read from/write to LevelDB

I know that Bitcoin Core uses LevelDB since 0.8 version. However, I couldn't find detailed explanation about how Bitcoin stores and retrieves from LevelDB. E.g. If B transaction uses an output from ...
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21 votes
1 answer
2k views

When was block 210000 generated and who solved it?

When was block 210000, the first block to feature halved 25BTC reward, generated and who solved it?
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19 votes
6 answers
6k views

Why can't we fight Bitcoin thieves by not accepting payments from hacked accounts?

Why won't we simply stop accepting payments from hacked accounts? We know their public addresses, right? Sure, hackers still will be able to compromise user's accounts, but at last that money won't be ...
  • 509
19 votes
4 answers
4k views

Does blockchain without currency make any sense?

I keep reading about private companies building blockchains for stuff like supply chain management, and about the billions of dollars that are going to be invested in blockchain over the next 5 years, ...
19 votes
9 answers
13k views

How to check Bitcoind block chain download progress level

I have installed bitcoind on ubuntu server, and when I run screen -x for btc it says error -10 blockchain is downloading. How do I know the progress level? currently 125600 blocks are downloaded, but ...
19 votes
4 answers
5k views

What is the "blockchain"?

What is the blockchain? I keep hearing about other "blockchain technologies", does this mean other cryptocurrencies or what?
  • 5,372
19 votes
4 answers
15k views

Reliable, efficient way to parse the blockchain into a SQL database

I need to generate a SQL database (preferably SQLite3) of every transaction that has occurred in the blockchain. Is there an efficient way to do this using open-source software? I'm attempting to do ...
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19 votes
3 answers
1k views

Countrywide Internet isolation, inevitable fork

Many countries around the world have provisions for shutting off the Internet as well as isolating itself from the Internet (where networking within borders still flourishes), any transaction ...
  • 1,580
19 votes
3 answers
1k views

How would the Bitcoin protocol be impacted if nodes only stored the blocks they cared about?

Right now, full clients of the Bitcoin network store every block ever generated (while "thin" clients instead rely on a node which does so). This greatly increases first-time initialisation for the ...
  • 14.4k
18 votes
4 answers
18k views

Why does each block store a Merkle root?

I understand how a Merkle root is calculated and stored in the block. But how do miners verify a transaction using the Merkle root? Here are 18 conditions that verify a transaction. None of them uses ...
18 votes
1 answer
3k views

Is the timestamp in the genesis block relevant?

Bitcoin's genesis block contains this text published in The Times on January 3rd, 2009: The Times 03/Jan/2009 Chancellor on brink of second bailout for banks According to the Bitcoin Wiki, this ...
  • 11.5k
18 votes
1 answer
16k views

Is it chain of headers rather than a chain of blocks?

We know widely used explanation of the blockchain: "Every block contains a hash of the previous block". The sentence above implies that since every block contains a hash of the previous block, ...
  • 421
18 votes
5 answers
2k views

How do you create a planet-specific cryptocurrency that will ignore longer block chains from other planets?

I'm sure that cryptocurrencies will play a huge part of the economy across the solar system, when we have colonized many different planets, moons, and asteroids. But there are problems with using a ...
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17 votes
2 answers
3k views

Is "Reclaiming Disk Space" already implemented? How effective will it be?

Some people are concerned about the scalability of Bitcoin. The blockchain already has reached nearly 1 GB to download and store, which is not exactly in the spirit of a modern thin client, especially ...
  • 3,487
17 votes
1 answer
11k views

What happens when you send a transaction that ends up in an orphaned block. Is it recoverable?

I've found a lot of information regarding orphan blocks, but I can't find an answer to this simple question. If I send a payment to a user and my transaction happens to end up in an orphaned block, ...
  • 2,182
17 votes
3 answers
28k views

Knowing a single transaction can you track down a Bitcoin user?

I have used this transaction to donate to Wikileaks. I have applied no special techniques to obsure my identity. How much information can find out about me on the blockchain. What tools would you use? ...
  • 1,010
16 votes
1 answer
3k views

Can private keys remain offline for their entire life?

I am new to Bitcoin and this question is based on 3 assumptions that may be incorrect. Assumption 1: If I understand correctly, the Bitcoin address is generated algorithmically independent of the ...
16 votes
3 answers
5k views

"Blockchain Explorer" software?

I've been going to blockchain.info frequently to check addresses, transactions, blocks, etc. But since I've already got the blockchain on my hard drive, this seems kind of pointless. Is there any ...
16 votes
1 answer
3k views

Should an end-user download the whole blockchain? Or is a “lightweight” client sufficient?

The average user normally doesn’t want to host a 3+GB file on his machine and wait for hours for it to download. What are the security risks of running a lightweight client? And how does this affect ...
16 votes
1 answer
1k views

Peergroup download of the blockchain stalls?

I'm using bitcoinsharp to build my client. I try to download the blockchain in a peergroup network. Download starts, but when progress is 98%, the download is stopped & the client is waiting (2 ...

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