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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58
votes
2answers
91k 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 ...
38
votes
3answers
25k 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 ...
61
votes
9answers
25k 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 ...
33
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2answers
11k 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 ...
52
votes
6answers
54k 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 ...
31
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2answers
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 ...
4
votes
4answers
7k views

What can I do when the blockchain synchronization is stuck at a specific block?

I hadn't started/used my Bitcoin client for ages. Now, whenever I start the client, it is downloading block 135407 and does not progress past it. What can I do?
70
votes
7answers
67k 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 ...
23
votes
4answers
4k 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 // ~...
35
votes
3answers
8k 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? ...
13
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6answers
6k views

Creating my own bootstrap.dat?

Since I have been tearing down and setting up bitcoin clients a lot for some experiments lately, I was wondering whether there is a simple way to speed up the synchronization with the network. One ...
25
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3answers
36k 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?
19
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2answers
3k 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?
10
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2answers
3k views

Will the proof-of-work system end when all bitcoins have been mined?

This article from ArsTechnica is claiming that Bitcoin is not such an environmental disaster, and one of the reasons they mention is that mining will come to an end. Ok, fair enough, there is an end ...
28
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1answer
10k 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 ...
14
votes
1answer
6k 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 ...
33
votes
10answers
26k 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 ...
10
votes
1answer
3k views

Strongest vs Longest chain and orphaned blocks

Satoshi writes at the bottom of page 3 of his white paper that "If two nodes broadcast different versions of the next block simultaneously, some nodes may receive one or the other first. In that case, ...
24
votes
1answer
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?
8
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3answers
2k views

At what point is a new wallet known by the Bitcoin network?

I was just showing a deterministic wallet to a friend who asked "At what point is the wallet known to the network?" and I could only guess by saying that it is known only when a transaction is ...
24
votes
2answers
6k 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 ...
28
votes
5answers
3k 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 ...
18
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4answers
5k views

What is the “blockchain”?

What is the blockchain? I keep hearing about other "blockchain technologies", does this mean other cryptocurrencies or what?
12
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2answers
3k views

How can I read information from the blockchain?

I don't want to use an existing service, like Blockchain.info or BlockExplorer.com. Is there some library out there that will let me read the blockchain programatically?
40
votes
4answers
44k 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?
21
votes
2answers
12k 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?
11
votes
1answer
10k views

How to transfer only the blockchain to a friend's computer?

After installing the bitcoin client (Qt) a friend got interested as well. He doesn't have as fast an internet connection, though, so I thought of burning some DVDs with the blockchains for him to have....
15
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4answers
15k 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 ...
5
votes
2answers
2k views

How is a blockchain split resolved?

Let's say two miners created 2 different blocks and broadcast them into the network. Now some clients see blockchain 1 and other blockchain 2 which are different from each other. I would like to ...
5
votes
1answer
3k views

Order of transactions within a block

Does the Bitcoin protocol guarantee that within a valid block, if transaction B spends the outputs of transaction A, A will always precede B? Or is it possible to have B before A?
9
votes
1answer
27k views

Whats the process of Creating a Block on the BlockChain

have been mining on pools and blindly going a long for the ride of > generating a block Can somebody walk through the process in simple terms of the steps involved in creating a block on the ...
7
votes
3answers
4k views

What is a step by step way to insert data in OP_RETURN?

I was following https://bitcointalk.org/index.php?topic=453086.0 for creating a message in OP_RETURN. I am able to decode my raw transaction, but on signrawtransaction it gives error: {"code":-22,"...
14
votes
3answers
4k views

Can Bitcoin-Qt be configured to trim the blockchain?

I run Bitcoin-Qt and Bitcoin Armory on a laptop. I don't have the space to store the whole 20 GB (or however big it is now) blockchain. I understand the need to run through the entire thing for ...
14
votes
3answers
6k views

How often does a block have only one transaction?

I was looking at blocks on blockchain.info, and came across this one with only one transaction in it: (the mining reward one) https://blockchain.info/block-index/512049/...
36
votes
6answers
8k 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.
9
votes
2answers
3k views

Is there a way to change the wallet.dat location without changing the entire data directory?

I know that Bitcoin supports the -datadir command line option which specifies that the wallet.dat and blockchain should be stored in a custom location rather than %appdata%\roaming\bitcoin but is ...
17
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2answers
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 ...
11
votes
1answer
2k views

How can an earlier block have a later timestamp?

Block #180966 has a timestamp of 2012-05-20 23:02:53. Block #180967 has a timestamp of 2012-05-20 23:02:13. How has the software permitted a later block to have an earlier timestamp than its ...
4
votes
1answer
1k views

What is a block?

I know bitcoin has a block chain that is from my best representation a list of blocks. I know the block holds many transactions. But i'm still very much lost as to what a block is and how a block can ...
0
votes
1answer
1k views

Reg: Watch only Address

I have been given " Watch only Address" by one of my friend.. To make the funds credited into my account or to use the BTC. What is way to get the Private Key..? Do we need to pay anything for the ...
6
votes
2answers
2k views

Why does the blockchain need blocks?

I think I understand the main parts of the Bitcoin blockchain. While I was explaining the concept to my girlfriend she asked me why groups of transactions are actually stored in a block? Every ...
41
votes
7answers
88k 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 ...
45
votes
1answer
6k 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 ...
26
votes
2answers
7k 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 ...
16
votes
8answers
10k 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 ...
11
votes
2answers
4k views

Transactions with a wait time (using nLockTime)

I'd like to know if there are transactions that can only take place at some predefined moment. In principle, it should be possible to use the parameter nLockTime to wait for a particular block number: ...
6
votes
2answers
2k views

When does a miner decide to stop collecting transactions and start calculating hashes to try to win?

I am confused about whether a miner chooses to wait for more transactions (more fees) or starts as soon as it receives the first transaction from the network. Once a miner has started calculating the ...
14
votes
1answer
9k 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, ...
5
votes
5answers
20k views

My client stopped synchronizing, how can I access my wallet?

My wallet has been stuck synchronizing for 21 days, my transfer is in the block chain but I can't get it to sync with my wallet. I've closed firewalls, uninstalled and reinstalled QT with back up and ...
4
votes
1answer
387 views

Mini-Blockchain proposal: How is the proof-chain secured against injections?

I have just finished reading the paper Purely P2P Crypto-Currency With Finite Mini-Blockchain by J.D. Bruce. While I got the impression, that the rolling blockchain as an idea might work, I was left ...