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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how to fix a fact that the recipient received the file so that the recipient could not dispute it?

how to fix a fact that the recipient received the file so that the recipient could not dispute it? How to do this by a smart contract? thanks in advance.
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Unable to interact with DApp deployed on quorum

I am unable to interact with contract using Dapp deployed on Quorum blockchain (using metamask). I am following "https://truffleframework.com/tutorials/building-dapps-for-quorum-private-enterprise-...
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Is it available to have an application that is managed by single Entity?

If For example Entity A wants to build a smart contract that manage a group of devices. But since each device uses pseudonym and he may change it later, is there any way to build the contract such ...
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How to read previous blocks data?

I'm new to block chain technology. I'm trying to store and read blocks using testRPC along web3.js. I'm able to get the latest block data but not able to fetch previous blocks data. Please some one ...
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Error while running web3 instance

I have a 2 node Ethereum system already setup. I am trying to have a web3 client talking to it. I installed web3 on a client machine and it gave no errors. However, I try to setup index.js and do ...
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how do I make users sign different strings with their private key separatelly

Here is the the scenario. Users come to my website and register(by using email and password). Then they login. After that, They add a new item(which has name and quantity fields). After Clicking ...
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107 views

Transaction successful but ether not transferred to destination account

I am following this article and everything works expected but ether is not getting transferred to the to account.Please find the logs below. eth.sendTransaction({from:eth.accounts[0], to:eth.accounts[...
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1answer
473 views

How to increase gas limit ethereum

I am facing this error : Error: exceeds block gas limit When i run below command it returns 5000. web3.eth.getBlock("latest").gasLimit so as per someone's suggestion 21000 gasLimit is needed to ...
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367 views

Running a full node of ETH

I need to run a full node of ETH and its bound tokens for an experimental exchange site. How will I do to differentiate ETH from others tokens ? Is there a way to download the ETH blockchain ...
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Initial Genesis difficulty on an ethereum clone

I've created an ethereum clone that i hope someday can become a public blockchain. This is working good so far, however i have a question regarding the initial setup for once i set this live. If i ...
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1answer
169 views

Accessing older blocks from Geth: Returned error: missing trie node 94d34

When my Nodejs script uses web3 to query a geth node running in a private Ethereum network for an older block, I encounter the error UnhandledPromiseRejectionWarning: Error: Returned error: missing ...
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Ger transaction details from the variable declared in smart contract

I have written smart contract in which I have declared one variable like uint256[] public UserIdList. And I am adding 3 userids while migrating that contract. Now, I am doing the mapping of user id ...
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129 views

how to automatically transfer funds in geth

I am trying to find a way how to automatically transfer funds from one address to another after new block is sealed. Scenario would look like this: 1. New block sealed 2. Check source account ...
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580 views

Error: VM Exception while processing transaction: revert due to require statement

I am new to ethereum world and trying to get some practise through my MSc Project. I am attempting to create an ethereum application for trading electricity. The contracts are the following: pragma ...
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862 views

Ethereum Blockchain Size calculation from Etherscan

I was looking into Etherscan.io charts of Ethereum Block Count and Ethereum Average Block Size. Both of them have the data since 07/30/2015 and if one multiply both time-series (Ex. 07/30/2015 - 644 ...
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1answer
190 views

Synchronous call of external contract function in Solidity

I have two Solidity contracts, where contract Caller depends on a second contract Callee. Contract Callee provides a public view function which checks the validity of a string (e.g. an password), ...
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Mining node stops working frequently

hello guys, i have created a private Ethereum blockchain network on Microsoft azure which has one transaction node and two mining nodes with configuration-For transaction node the ram is 8gb and one ...
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1answer
369 views

How to connect not local node to private Blockchain?

Is there any way to connect NOT LOCAL node to running private Blockchain? So, there are 3 virtual machines in one local network. They are syncronized private blockchain. They have static-nodes.json ...
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1answer
47 views

smart contract for each individual user VS single smart contract for each kind of user

I am learning to build Dapp in solidity. The use case is as follows : There are two users on the platform(Dapp) 1. Service Provider: the one who provides services to the customer such as electricity, ...
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Mist: how to view private key of an account

Question: How do I use Mist to extract the Raw private key of an account. The account is password protected (if that makes a difference I don't know). Elaborating: I made an account with mist that ...
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2answers
38 views

How do we get latest value of a key from blockchain?

I want to understand the basic working of storing a value of a key that can periodically update its value in blockchain. For example, if the value of 'a' is 4 today and is stored in blockchain, then ...
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1answer
135 views

How block are validated in a private blockchain

I have running a private blockchain with 4 nodes, and when i'm creating my Dapp, i have specified for the web3 address only one node ( Ip; port, RCP) So, my question is , how the others nodes ...
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2answers
87 views

Massive Download [ETH] smart contracts

This question have just been published in StackOverflow as well, but you might be able to guide me on a better direction: I'm looking for the most valid path to download and keep downloading every ...
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1answer
43 views

Mist can't run on a testnet?

When I install Mist, and after a bit of loading, it starts downloading the blockchain for the mainnet, but when I change the network, I get an error that it's not connecting. If I try to restart mist (...
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How can I show on web3j a list of all the instructors added on my blockchain?

I need to show on an html a list of all the instructors that are set up on the list pragma solidity ^0.4.18; contract Owned { address owner; function Owned() public { owner = msg.sender; } ...
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158 views

Unable to send ether to account

I am trying to send ehter using this code web3.eth.accounts.wallet.add(privateKey); web3.eth.sendTransaction({ to:someAddress, from:onwer, value:amount*1, ...
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1answer
362 views

Posting data from raspberry pi on blockchain and retrieving it back

I am new to blockchain technology. I just want to know if it is possible to post the data from raspberry pi on blockchain (ethereum) and retrieve the posted data for viewing. My question is if its ...
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signing a transaction on web3js with private key and broadcasting to nodes

I am having an issue with ethereum based project. I made web3 API to communicate to the blockchain. I did this two ways. both call the same function on same address: METHOD 1 (Using Unlocked ...
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1answer
227 views

Resource allocation and smart contracts

I'm wondering if the following scenario could work with smart contracts. I'm very new to Blockchain so what I'm saying might sound too silly. I have 10 users who are sharing a common resource. There ...
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1answer
424 views

How ERC20 Token balance are recovered during Ethereum chain rolling-back

My Answer: Ok, the problem is really with Ganache ... If I use geth, everything is alright. ... ... sorry for your time ... ---------------- The Original Question -------------------- My ...
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has anyone written a nodejs server side component to listen only for Ethereum Events?

I tried the below code to run it using the pm2 module, as nohup command as well. But, this doesn't seem to work. I saw this, but no code is present. so this is what I'm trying to accomplish. I want ...
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2answers
50 views

How can you tell if a mined transaction made permanent changes?

I have set up a private ethereum blockchain and I have defined a new coin. When I send coins from one account to another through the smart contract the transaction is always mined even when the coins ...
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53 views

Integrate more then one user with one ethereum account

I have many users inside the organization and I want to use same ethereum account for all the users , but with different usernames, so it there anyway to do that ?
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How many tokens are transfered actually when we are using decimals

I have a code below and when I am transferring 1,695,000,000 to a particular address, so actually 0.000000001695 are being transferred. Why is it so? Does that mean to transfer 1.695 billion tokens I ...
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223 views

How can I insert values from web browser Firefox or chrome like html and js to ethereum blockchain?

How to save values from an HTML form into block chain through a browser, I have gone through different tutorials, but it is confusing, how this go-ethereum blockchain and smart contract can access ...
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263 views

Multiple addresses initialization in constructor function

Usually we have one address initialization in constructor function. And that address becomes owner of the contract. While studying erc721 token and going through several examples online i found ceo ...
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257 views

web3 (then property) in ethereum node

Would you please help: When I run the below command in my nodejs console I get the below error: (I am using web3 0.20.0) on Windows 10 web3.eth.getAccounts().then(list => {accts = list}) ...
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324 views

What is a standard implementation of upgradable ethereum Token contract

I've readed some code of ethereum Token contracts, such as this one In this code, it does 2 things for upgradable: a contract interface or something like a "abstract contract" called "UpgradeAgent" ...
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1answer
560 views

Deploying Solidity Contract Using Web GUI and web3

Any guide or step by step Tutorial for deploying a solidity smart using a GUI and accessing the meta mask account ? Please Help
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525 views

Deploying a smart contract using DApp

I am new to the development of DApps on ethereum blockchain. I want to make a contract Management System in which users can generate their own tokens and crowdsale using my web application. I am able ...
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1answer
345 views

how to connect to a private ethereum testnet with blockcypher

our project uses blockcypher to create eth wallet which can transfer eth now.Blockcypher supports ETH main network and its own testnet. Is there any way to connect the blockcypher node to a custom ...
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1answer
1k views

I sent PRL token to contract address instead of wallet address

I am wondering if i can recover the tokens. I sent PRL tokens to contract address 0x1844b21593262668B7248d0f57a220CaaBA46ab9 instead of myetherwallet address from kucoin exchange wallet. :-( Are ...
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4answers
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Restricting payment from one account only

I am a beginner in ethereum DApp development and I am testing my Contracts in Remix IDE. My question is that can I restrict only one account to pay for all the transactions happening on my application ...
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2answers
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how to get the hash address of previous block while adding a block into blockchain?

In blockchain every block is having three things, Hash address of the previous block Hash of the all the transactions those are part of the current block Nonce, a random value which can be got ...
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290 views

Where does geth store data except for the AppData\Roaming\Ethereum folder?

The AppData\Roaming\Ethereum folder on my computer weighs 5GB, but geth has reduced my disk space by a lot more than 5GB. Where else does it store data?
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Can I access last mined block if my node is not there yet?

This might be a stupid question, but I'll ask anyway... I'm currently connected to Ropsten and when I execute eth.blockNumber it says 1853682 (I'm like 300000 blocks away from current last mined ...
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404 views

how does digital signature functionality in blockchain fulfil the requirement of user identification?

As we are aware that blockchain is a decentralized application and it is tough to implement user identity mechansim in decentralized application so we use digital signature to verify the identity of a ...
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127 views

Is Merkle tree applicable at block level also?

As per my understanding, Merkle tree is applied in case of transactions. Through Merkle tree we generate root hash transaction from all the transaction present in a block. So does it work the same way ...
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1answer
102 views

testing the hello world application on a different computer when the compute crashes/node not working

I am new to the blockchain technology. I want to test the blockchain functionality of a decentralized ledger. I have created a hello world smart contract(on solidity, geth, mist browser) on computer ...
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335 views

Unlocking Ethereum wallet using Geth JSON-RPC

When I use ETH with JSON-RPC I have error "message": "authentication needed: password or unlock» and If I manually unlock I have other error "message": "insufficient funds for gas * price + value" Any ...

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