Questions tagged [blockchain]

The Ethereum blockchain is a distributed database based on the Ethereum whitepaper specification and stores both the full transaction list and the most recent state.

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2answers
3k views

Where are the variables of a smart contract stored?

we all know that we can write smart contract with solidity in ethereum such as: mapping(bytes32 => bytes32) private userPasswds ; event RecordReturnResult(bool res); /// @dev new the ...
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1answer
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Getting private keys of geth accounts

Just the opposite of this question How to import a plain private key into geth or Mist? I would like to know how can I obtain the private keys of the accounts created with geth in this way: $ geth --...
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What are the trade-offs between Ethereum's public chain and private, permissioned chains?

I see a large number of news stories and companies talking about the possibilities for private or permissioned blockchains. What are the key tradeoffs between using a permissioned/private chain and ...
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1answer
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How many contract are currently deployed on the Ethereum blockchain?

I was recently asked what percentage of transactions represent smart contract deployments on Ethereum, and had no immediate answer. It is probably easier to ask how many contracts are currently ...
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How to use web3 to send money from wallet A to wallet B?

var myContract = web3.eth.contract(abi); var address = contract address; var contract_data = myContract.at(address); var sender = '0xd3aaa525c087978133abb517593ea334f16abd1f'; var receiver = '...
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1answer
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How to query the amount of mining reward from a certain block?

I want to write a script to analyze mining rewards. What is the best way to query for the amount of mining rewards of a certain block? It seems possible to query the address of the lucky miner: web3....
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1answer
2k views

Set watch for ethereum address transaction using web3js

I want to set watch for my public address. So i can get all transaction for that address. My code is: var filter = web3.eth.filter({ address: ["0x2A7146700BCe4A574eE36D5e9cd6CF7d8871aEB6"] }); ...
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1answer
423 views

Is it possible to embedd the UI of DApp in the blockchain?

I have read the answers for this question as well as their linked resources, but I didn't found the answer for the following question: is it possible to embedd the UI of ÐApp in the blockchain? If I ...
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1answer
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How can I store big files on the blockchain?

I can hardly create transactions larger than 100kiB. I am wondering, is it possible to store huge files (several MiB or GiB) on the blockchain? If so, how?
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1answer
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Difference between Dapps, digital wallets and smart contracts

What is the difference between Dapps, digital wallets and smart contracts? I have just started learning ethereum. So there is much of confusion for me. From my understanding: Dapp is an application ...
2
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1answer
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sendTransaction from iPhone app

How do I call sendTransaction from within an iPhone app? I was thinking of running a web to Geth proxy where the iPhone app would call the Api exposed by the proxy which in turn calls my self hosted ...
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4answers
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getting error on max invalid genesis file: hex string has odd length

I am trying to create a genesis block on my mac for a local ethereum network but I am getting the error: invalid genesis file: hex string has odd length when i do it. My code is the following: { ...
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1answer
629 views

Blockchain size projections [duplicate]

What are the growth projections for the size of the Ethereum blockchain? Is it too early to start talking about the need for side chains? Will economics naturally pressure DAPPS to either choose the ...
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Missing trie node only on some blocks > is it possible to resync a specific Block?

I'm trying to trace some transactions and I'm getting the "Missing trie node" warning only on some specific blocks, but not on others I've read a solution that suggests to delete the chaindata folder ...
4
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1answer
669 views

What was the first block mined with Homestead?

What was the first Homestead mined block? 1,150,000 was planned if someone can confirm? https://ethereum.stackexchange.com/a/1834/264 can one see that its a homestead block by some property? ...
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1answer
674 views

What token address do I use if I want to sell an ERC20 token on a different exchange? Its original address or its address on the other exchange

I really need help with this one to avoid logic errors. I am on the Kovan testnet. I bought 4 units of DAI token on Uniswap exchange(0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D) for 0.111 Ether and ...
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scheduling of smart contract functions

I am reading the alarm clock documentation http://docs.ethereum-alarm-clock.com/en/latest/ but there are things I don't understand. I have a dapp where the smart contract has different functions. For ...
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How to set up a Private network and connect peers in geth?

I am trying to setup a private network and trying to connect peers. Currently I'm trying it on my laptop and desktop (both of them are connected to different internet). I run the below command in ...
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2answers
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Relationship between Transaction Trie and Receipts Trie

Reading through the Yellow paper, I can see that each block header includes the Keccak 256 hash of the root of the trie for transactions and transaction receipts. I am struggling to understand how and ...
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2answers
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In Mist browser how can I move the data (blockchain) to another drive on Mac OSX?

My Mac "System" drive is almost full. As I actually have two drives, I want to move the blockchain from the default location to the second drive. How can I do it ?
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4answers
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Can I download the whole blockchain from somewhere?

Bitcoin used to offer sharing/downloading a bootstrap.dat which contains the whole blockchain. Are there alternatives to getting it trickling through the peer-to-peer network? Can I just download it ...
20
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6answers
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How to find contract's address?

I successfully setup a private blockchain and created the "hello world" contract according to tutorial from etherium web site. One thing that I can't figure out is how to find the contract later. I ...
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7answers
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Question on the terms 'distributed' and 'decentralised'

I am writing a paper on distributed ledger technologies, an umbrella term I have borrowed to put everything that has any relation to blockchains and distributed consensus. Under this umbrella term I ...
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What is the exact data structure of each block?

is there any document / diagram describing Ethereum block structure in similar way as https://en.bitcoin.it/wiki/Block? I know I can find implementation at https://github.com/ethereum/pyethereum/...
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What diagrams exist to illustrate the Ethereum blockchain creation process?

I have found the below diagram (and this explanation) useful in understanding how blockchains work in general: [Illustration by Matthäus Wander (Wikimedia)] This answer goes on to say that ...
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6answers
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Best way to test a smart contract

I just want to deploy and call a simple sample smart contract only for testing purpose. Do I need to download the entire ethereum blockchain? Its too huge and takes too long to download. Can someone ...
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3answers
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How can you parse blockchain files stored in a local node to get blocks and transactions details?

I want to get all details of blocks and transactions without using event logs. For example, I want to get a list of of transaction data which are sent to a specific contract. How can I parse local ...
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2answers
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'authentication needed: password or unlock' Error when trying to call smart contract method via web3

I am trying to call the smart contract method (deployed on remote ethereum account) from my nodejs DAPP, and getting the following error- Error: authentication needed: password or unlock at ...
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3answers
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Why do we need both nonce and mixhash values in a block?

Looking over the sample genesis blocks, I notice that both nonce and mixhash values can be assigned independent values. Reading the yellow paper it's mentioned that: mixhash: is a 256 - bit hash ...
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3answers
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What is actually removed during a contract suicide, and why doesn't this cause the blockchain to change?

I'm trying to get my head around how contract suicides work, and what actually happens during them. I understand why we use them. This post states that when the SUICIDE opcode is executed, the data ...
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1answer
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Executing a Smart Contract in a Mobile App

I am new to the world of Blockchain and Ethereum has indeed become a second name for open source Blockchain. Right now I am trying to grasp the concepts and there are really many wonderful blogs but ...
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How to reduce chaindata database size?

Currently chaindata size is more then 10.02 GB. Is there any solution to reduce the size of stored data? Is there a way to store particular database and keep entirely the functionality of client (e.g....
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1answer
887 views

Why are contracts limited to only the previous 256 block hashes?

Why are contracts limited to only the previous 256 block hashes using the BLOCKHASH opcode (and corresponding functions in Solidity and Serpent)? Why does another contract, such as this, need to be ...
7
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1answer
2k views

Is the size of the Ethereum blockchain a problem for full nodes in the coming months?

In August 2017 the size of my chaindata directory was about 12GB. Now it's November and my chaindata directory is now 220GB - as per expectations with the growing popularity of Ethereum. I run my ...
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2answers
934 views

Is it recommended to run Ethereum supernodes?

In the early days of bitcoin there was a demand for system administrators who were able to run supernodes to support the network with stable nodes and high bandwidth. Litecoin is still recommending ...
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2answers
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What is the order of operations to verify a transaction?

I am not asking if all nodes run each transaction. I'm asking for a rough time sequence of events. For example, in the case of a double spend attempt, and the double spender is colluding with the ...
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What is a Shard?

Proof of Stake brings new concepts to the Blockchain ecosystem. In the dictionary "Shard" is defined as "A broken piece or fragment, as of pottery or glass".
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4answers
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Error “no key for given address or file” when unlocking coinbase account

Using json-rpc eth_unlockAccount() method I can unlock everyone of my node accounts except coinbase. When trying to unlock coinbase account, geth responds with the message: no key for given address ...
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2answers
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How is the Two Generals Problem solved with proof of work?

Here is an email where Satoshi Nakamoto explains how PoW solves the Byzantine Generals' problem http://satoshi.nakamotoinstitute.org/emails/cryptography/11/ The proof-of-work chain is a solution to ...
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1answer
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Creating multiple contracts or Single contract with struct

I would like to understand which of the following patterns is better. Say my use case is to have two types of users in my platform buyer and seller for a product, with regard to my architecture Im ...
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2answers
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How do block explorers actually work?

How do block explorers interface with a chain differently than full nodes? Would it be possible to integrate block explorer features into a full node implementation in the future?
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1answer
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How can you implement two way pegged Ethereum <-> Ethereum sidechain?

If you want to create an Ethereum sidechain which is two-way pegged to main (public or private) Ethereum, how can you implement sidechain? For example, How can you lock ether? How can you verify ...
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3answers
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How to execute Smart contracts on a private Blockchain network

I have created a private Blockchain network on my Windows system with one node. I have created accounts and was able to transfer ethers across them. Now I want to deploy smart contracts on this ...
4
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1answer
10k views

Account is locked. How to unlock it using json-rpc? [duplicate]

When trying to send a transaction through json-rpc interface on a geth node (version 1.4.10-stable-5f55d95a, running on testnet) using eth_sendTransaction I got this error message: -32000 [message] ...
4
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1answer
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How Ethereum estimate the gas for running a contract?

I am new to Ethereum. I know gas limit and gas price well. but still confused in when sending a transaction to run a deployed contract, does Ethereum suggest an estimation of how much gas limit is ...
4
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2answers
847 views

Blockchain use case in healthcare

I am new to blockchain. I am trying to understand the use cases of blockchain as a technology in healthcare. There are number of articles about different cryptocurrencies. I was going through this ...
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2answers
1k views

what is Sha3Uncles?

What is Sha3Uncles field in the blockchain? And, why is it the same for uncles 3,4 and 7 ? And why ParentHash for these uncles is also the same ? https://etherscan.io/uncle/...
2
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1answer
355 views

Can contract code query the block chain?

Is it possible to have a contract whose methods iterate through the block chain? in that they can read block/transaction related data and make transactions based on them? Or monitor the block chain ...
3
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0answers
449 views

Ethereum blockchain size as of March 2017 (geth --fast and others) [duplicate]

What is the size of the Ethereum blockchain as of March 2017? I am just starting with geth --fast -cache=1024, but I would also be interested in other clients or other downloading methods. I know ...
3
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3answers
1k views

Is there a way to know the contract creation Address from a the transaction?

I know that in the transaction receipt I can get the contract address by getting a transaction receipt from a generated transaction. But I am wondering since smart contract addresses are ...