The blockchain is a list of all transactions that have occurred using the Bitcoin currency. Please don't use this tag for the service named 'blockchain.info'.

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Blockchain Pairing API

Have anyone of you figured out how can we use devices pairing in 3rd party applications? I've found that pairing QRCode looks like this: "1|<blockchain_login>|<some_hash>", where ...
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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, ...
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Is it possible that someone forks the chain?

I'm not sure I understood everything but all the clients always keep the longest chain, ok. So, what happen if an evil person inject bad transactions in a block and successfully mine it (given the ...
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Confirmation limit

When seeing transactions I see that the number of confirmations keeps increasing without any limit. I wanted to know if there is any time limit on including a already confirmed transaction in a block ...
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How To Lower The Disk Space Needed For Full Blockchain?

I'm looking to run bitcoind on a virtual machine. However the main nets Blockchain size is over 21GB, and growing. Is there a way to compress this down or lower the amount of disk-space needed for ...
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New To Bitcoin…Please Help! Bitcoin not received from sender to Armory Wallet!

I am in desperate need of assistance! I am new to Bitcoin so please apologies for the lack of knowledge in these matters guys....We all have to start somewhere ;) I sent my Bitcoins from the ...
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“Watch only” wallet and a private key

i recently bought a BTC wallet from my friend, it has a cold storage wallet ("Watch only") and a private key (which is a bunch of numbers and letters) for Blockchain. How do I use it in Blockchain? ...
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Blockchain and Bitcoin client difference of amount

I just made a transfer of 0.06 BTC, you can look it up on Blockchain.info The problem now is that my receiving client (Multibit) doesn't show those 0.06 BTC, it only shows 0.0001 BTC have been spend ...
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Can you assume that all inputs to a Bitcoin transaction are controlled by the same person?

When you are looking at a Bicoin transaction in the block chain and it has inputs from multiple addresses is it safe to assume that those addresses are all controlled by the same ...
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What percentage of Bitcoins stored in a multi sign address?

I am looking for a statistic of the usage of multi-sig addresses over time. More concrete: what is the percentage of Bitcoins stored in a multi-sig address over time.
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What is current size of various databases in Bitcoin Core as of July 2014?

This question is related to question: What is the database for? What is size in MB of: blockchain itsef - blocks/blk*.dat blocks/index/* chainstate/* blocks/rev*.dat Is the size of chainstate and ...
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Are NXT messages stored on the blockchain and are they encrypted or publicly viewable?

Are nxt messages stored on the blockchain? What is the character limit on these messages? And are the messages encrypted or publically viewable? If they are public, is there a site to just view all ...
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getrawtransaction doesn't work for every transaction with -txindex=1?

i put txindex=1 in bitcoin config and reindex blockchain after that when i call getrawtransaction for some transactions didn't exist in my wallet and work well like: [Working] getrawtransaction ...
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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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How big is the NXT blockchain in disk usage compared to the Bitcoin Blockchain as of June 2014? And rate of increase?

Currently I'm looking for the disk usage size of the NXT and Bitcoin blockchain size as of June 2014 and the current rate of of increase every day/week/year?
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What determines how many transactions end up in a given block?

What determines how many transactions end up in a given block? Blocks can have various numbers of transactions, so what decides how many are in a certain block?
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How do I prevent Bitcoin-qt from having to keep reindexing the blockchain?

Is it likely that anti-malware or anti-virus software is causing this issue? (I have told such programs to exclude the Bitcoin folders from scans)
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What is the best way to implement withdrawal in online service?

Suppose we have a service, which holds user balance in Bitcoin. How to implement withdrawal from bitcoin perspective? Which RPC call to use? How to archive transaction to have a proof of sending ...
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blockchain - strange problem

I have Windows 7 and i’m using the bitcoin-qt client v0.8.6-beta. Last night i tried to open up the client – but there was a message that said i had some issues with the blockchain. Which is weird, i ...
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Custom altcoin won't sync with node and neither will accept a miner connection

I forked the BlackCoin source, changed the ports, generated the genesis block, merkle, blah blah blah. I set up a node on a DigitalOcean server and compiled my coin daemon there as well as on my local ...
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Created genesis block and set up node. How to mine?

Everything seems to be going well creating my altcoin for fun. I forked the BlackCoin source on Ubuntu, successfully mined a genesis block, recompiled. I bought a droplet over on digitalocean running ...
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Why is my new altcoin trying to connect to peers and sees almost 200k blocks remaining?

I downloaded and forked the Blackcoin source code. I changed all of the references to BlackCoin, changed the pszTimestamp string along with the current Unix timestamp. Then, I successfully mined the ...
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Miners produced/ing duplicated hash values

This transaction is contained in two MainChain-Blocks: https://blockchain.info/tx/e3bf3d07d4b0375638d5f1db5255fe07ba2c4cb067cd81b84ee974b6585fb468 On Blockexplorer there is a note of this anomaly: ...
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what is Create wallet using blockchain api (PHP)

Im wondering to know, what is use of Create wallet programitically Block chain API Block Chain api here What it will provide? Where can i get the api code? Any tutorials ? Can i provide my ...
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How to find a block containing a transaction using transaction hash only?

Well, the title says it all. I have a transaction hash and I want to find this transaction in the blockchain. I am working with bitcoinj. I am probably missing something very obvious here, but I ...
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Purpose of a BlockChain in local wallet application

I have installed the BitCoin wallet application on my PC, so that I can cold store my BitCoin. It's "Synchronizing with the network" and has 272 weeks of BC left to download (painfully slow!!) What I ...
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How many coins does Satoshi have? [duplicate]

There are rumors that the creator of Bitcoin, Satoshi Nakamoto, currently possess as much as 1.5m bitcoins. What are the steps involved to determine / guess how many coins Satoshi has?
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How to choose address in BlockChain Android Application?

If I want to receive funds using the Blockchain Android application I click on the arrow on the top of the screen which brings up the Request Bitcoin screen, showing the QR-code for easy scanning. ...
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How to find utxo?

I might be over thinking this, but I'm trying to figure out the best way to build an unspent output pool. Should I just naively parse every block? Every input gets removed from the hash set, and every ...
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Is there database of orphaned blocks?

Is there database of orphaned blocks? https://blockchain.info/orphaned-blocks does not work right now Does anybody keep them? Also I am looking for those transactions which were not included in ...
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How can “undo” bitcoin transactions be “private”?

BitUndo private transactions: If you choose to make your undo transaction private, nobody will be able to see that you tried to undo a transaction, unless it succeed. You have to know that a ...
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Wallet programming, search transactions by address

This may be a silly question, but I keep running in circles. Using either bitcoind or JSON-RPC is there a way to search all transactions involving a address hash? I understand every wallet and most ...
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How do we check the time when a transaction hits x confirmations?

Consider the transaction 948a427.. which has 3341 confirmations as of now: We can see that the time the relay is received at 8:36:30 and it has one confirmation at 08:50:04 (after 14 minutes). How ...
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A clarification about Wallet and Addresses (In Armory)

I've just a dumb (Probably) question about bitcoin wallet and addresses (in Armory): If I've understood correctly (Correct me If I'm wrong), a wallet works as a "container" where you can store ...
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Optimising the inputs for a transaction

I have a list of unspent outputs. Let's say: 0.4 BTC, 0.6 BTC and 1.0 BTC. Now I want to create a new transaction for a 0.5 BTC. How I understand it, it would be best to take the 0.6 BTC output as ...
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How does a Bitcoin client know its transaction has been accepted by the whole network?

Say Belly, Alice and Teddy are Bitcoin clients. Belly makes a transaction to send 1 btc to Alice. He broadcasts this transaction to the P2P network. Teddy calculates a valid hashcode and add Belly's ...
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How can Blockchain.info wallet send unconfirmed bitcoins?

So i just opened a Blockchain.info wallet after years of using Bitcoin-qt. My Blockchain.info wallet had an empty wallet, i sent some bitcoins to it and right after that without waiting for ...
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How will the new Internet Neutrality Act affect Bitcoin?

How do you think the neutrality act that is being talked about as I write this post will affect the Bitcoin community. Not only in transactions, but mining, how will it affect Bitcoin economically ...
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SHA256 * 2 on header - what am I doing wrong?

I've been experimenting with the php code here: https://en.bitcoin.it/wiki/Block_hashing_algorithm (after correcting the small bug of $x=; to $x=""; ) With these blocks 0 and 125552 (for example) it ...
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How Is Block Assembled?

I think I understand mining well enough, but what I don't get is how the blocks of transactions are assembled. According to this post - What exactly is Mining? - the miners assemble the blocks and ...
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Transaction verification up to coinbase?

Do full nodes verify the entire transaction chain up to coinbase when verifiying a single transaction to be included on the block which they are working on ?
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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: ...
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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 ...
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Is a full blockchain fork possible?

Let's say someone creates a blockchain fork starting from the genesis block, when the difficulty was absurdly low compared to today; then he starts mining new blocks from there up to the current block ...
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Do receiving addresses expire on Multibit?

Okay so I have tried Resetting Blockchain and Transactions plenty of times. The only thing is I used an old receiving address that I used about 2 months ago. Do these addresses expire? Can they only ...
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What Prevents the number of Bitcoins from being increased? After 21 Million? [duplicate]

Can the bitcoin MAX_MONEY attribute simply be changed from 21 Million to a higher number? If not what prevents this from being done? What would happen to existing addresses and accounts if MAX_MONEY ...
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Reclaiming Disk Space [duplicate]

According to section 7 of the original bitcoin spec. by Satoshi: Once the latest transaction in a coin is buried under enough blocks, the spent transactions before it can be discarded to save ...
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How many addresses are in blockchain? [duplicate]

I understand that client like bitcoin-qt can generate addresses indefinitely, but only true or active addresses are in blockchain. How many addresses are in blockchain? Is somewhere statistics data ...
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Running Bitcoin Core for first time

I was using the official Bitcoin client some time ago. It was version 0.5 I think. Then my computer crashed and didn't use Bitcoin for a long time. I was lucky because I had a backup of the wallet. ...
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How to minimize risk when accepting zero confirmation payments?

I'm trying to setup a way of accepting Bitcoin payments in real life situations, where waiting for confirmations is typically not an option. I understand this is never 100% risk free (especially with ...