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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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Want to understand token migration

Can anyone please explain the process of Token migration from one network to another network, Like omesi go and tron has done. they first lauch there own ERC20 token over ethereum and later migrated ...
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15 views

What are blockchain interview quesetions? [on hold]

What are some best blockchain, ethereum and smart contract interview question that I must know ?
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14 views

What is deployed smart contract address in solidity?

In remix IDE when we deployed the contract there is address on it. What is that address and what that address is used for? Like Ethereum account address is use for transaction and identify the user ...
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10 views

What can I write in the app.js to exchange with ethereum smart contract

I want to send data to storage it into blockchain from file .txt automatically every hour. this is my smart contract : pragma solidity ^0.5.0; contract Storagedata{ bytes32 data; function setData( ...
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1answer
15 views

Getting the transaction hash on function call

I am new to Solidity, Web3, and Ethereum. I am trying to build a web application through which users can upload a file to IPFS, then store the IPFS hash in the blockchain. I am using the React truffle ...
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1answer
19 views

Does nonce same for all node?

Suppose in blockchain network we have 5 nodes and we have new transaction done by first node of network, so now rest of 4 node will mine the transaction to commit it in blockchain network, will the ...
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22 views

How to add smart contract functionality to my blockchain?

I am currently developing my own Blockchain in C++ to just more understand the technology. I am using the Ethereum Blockchain as an example. One of the things I already copied from Ethereum blockchain ...
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1answer
15 views

How merkle tree is used to verify transaction in blockchain

May any one give example how merkle tree is used in blockchain to verify the transaction? I confused because validation of data in ethereum is done through the proof of work where you find the nonce(...
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3answers
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How data is secured on ethereum network?

Blockchain is distributed decentralized database and same data is present on every node on network so now anybody on the network can see my data, so how it is secured over blockchain network?
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How to prepare for blockchain interview?

I am learning blockchain and want to pursue my career on blockchain, so what will be the best way to do that? What certification I must do and what think I should cover? appreciate all your career ...
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1answer
25 views

What is difference between geth, myEtherWallet and etherscan

I am new to blockchain technology and learning it, there are many terms of blockchain which confused me like geth client, meta mask, etherscan and myEtherWaller. I used geth it's a ethereum client to ...
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1answer
20 views

How to pass a document as function argument(upload document)

I am working on a project in solidity where I want to generate a SHA256 hash value for the document. So which means when I choose a file using a function the function should return the hash value. ...
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10 views

Parity synced at not existing block 4839212

I have problem with parity, cant get synchronization in archive mode to end, anything, changing arguments, max-, min-, snapshot-peers, parity verisions do not help. I have blockchain in archive mode ...
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1answer
18 views

What happen when I format my blockchain setup PC? [on hold]

Suppose I have ethereum blockchain network setup in my PC and when I format my PC how I will recover my data? Normal in client server architecture my data doesn't depend on my PC whether I format or ...
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1answer
20 views

Automating user data storage on a blockchain

I have a smart contract that contains a function to store data onto the blockchain. The function stores two integer variables to the blockchain. Now, I can manually store the values from the remix-ide ...
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1answer
22 views

How to open metamask erc20 transfer window using web3 apis?

In my frontend I have 'withdraw' and 'deposit' buttons. I want to display the metamask screen that comes after clicking on the deposit and send buttons (of metamask) when the user clicks on the ...
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1answer
10 views

If i pay some service on certain dapp, does this tx can be reverted because of confirmation?

I paid and got service from dapp. does dapp wait until enough confirmation is settled? or not, is it possible that tx can be reverted?
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22 views

where is data store in blockchain? [duplicate]

for example we have contract like this: contract Sample { string public name = "Moore ath John Yuur Gha"; function set(string memory _name) public { name = _name; } ...
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1answer
12 views

How smart contract execute when receiving two transaction in the same time?

When a smart contract receives two transaction by different users, what is the transaction that the smart contract will deal at first ?
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1answer
17 views

How does Ethereum ensure that “users can own their data, and your apps don’t spy and steal from you”? [closed]

What features in ehtereum would ensure that the Dapp would never spy on you or steal your data?
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1answer
12 views

When is chain data (length) compared between nodes? Is there any way to control this?

I am trying to use an ethereum blockchain in a multiagent network. I would like to control when information is exchanged between nodes to keep the network synchronous, so I am trying to figure out how ...
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2answers
16 views

Decrease the time between new blocks in Ethereum Development

I'm trying to create a DAPP (with docker-compose) which will require many transactions, and I am currently experiencing nonce problems with my Transaction Manager. However, I'm not looking for help ...
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19 views

How can I store the hash of a set of data in the ethereum and make the chain validated always?

I am working on a University Management System and I want to develop the system using Centralized Database like Mysql and to keep the data safe I want to use blockchain to store the hash of the data ...
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1answer
38 views

how execute smart contract step by step?

I have a few problems understanding the step of execution of transaction in smart contract. 1-When a user send a transaction to smart contract, this smart contract is not executed immediately instead ...
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43 views

How to decode SHA256 hash value and retrieve data in Solidity

I am working on a project in solidity where i am encode a string to SHA256 hash value, and now i want to decode SHA256 hash value and retrieve the actual data. please help hoe to do it. Below is the ...
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19 views

Store data on ethereum blockchain from a text file

I have a simple smart contract running over a local Ethereum node. It has two functions: one for sending data and another for retrieving it back. I have a text file and want to send data from it to ...
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1answer
20 views

How to store and encrypt Keys?

I am developing chrome extension like metamask for the private Chain. I have generated the keys and using localStorage to store the Keys. But I am not sure whether I am going correct or not for ...
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1answer
14 views

Getting error in Deposit function in smart contract : The constructor should be payable if you send value

I am getting the error while deposit the amount in remix. Following is my code pragma solidity ^0.4.19; contract Savings { address owner; uint256 deadline; modifier onlyOwner() { require(...
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1answer
19 views

Truffle migrations - UNABLE TO MIGRATE (Error: Deployment Failed)

The compilations goes well on the Rinkeby testnet using the command geth --rinkeby --rpc --rpcapi="personal,eth,network,web3,net" --ipcpath "~/Library/Ethereum/geth.ipc" --syncmode light --cache 64 --...
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1answer
27 views

How to connect Trust Wallet in Javascript?

I want to use TrustWallet for payments in my project for mobile users. I saw the documents related to TrustWallet web3 API but not getting how to use it in javascript. Can anybody help me with the ...
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1answer
12 views

How to redirect to Etherscan website when transaction completes?

In my project, I am doing a transaction by using ethereum.send({ }) method from web3 in javascript using metamask. After the transaction completes I want to display the link to the user in label ...
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22 views

How can I create an Ethereum blockchain fully with the change of the name geth wallet? [on hold]

How can I create an Ethereum blockchain fully with the change of the name of geth wallet? I have already created a private blockchain, but I don’t know what to do next, in order to own a full-fledged ...
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2answers
27 views

Mapping primary key of each struct in array to them-self

pragma solidity ^0.4.17; contract Campaign{ struct Transaction { address Creditor; uint Amount; } Transaction[] public Transactionss; mapping(address => Transaction) ...
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1answer
21 views

Where to store data when creating a blockchain based solution?

I have a question regarding the storage of data when creating a Dapp. For example i create a real estate website on ethereum blockchain where people will buy or sell properties on the basis of tokens ...
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1answer
20 views

Calling a function from another contract is not working. But calling the function from deployed contract is working

I have a problem with calling a function from another contract. I don't know why it is not working. Contract DateTime(https://github.com/pipermerriam/ethereum-datetime) is a util for converting ...
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3answers
19 views

How can i send data to Contract's function with sendTransaction?

i hava contract like this pragma solidity ^0.5.0; contract Sample { string public name = "sample"; function set(string memory _name) public { name = _name; } function get() ...
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1answer
31 views

How does Ethereum calculate balance for a new transaction if there are already unconfirmed transactions in the mempool?

Whenever a new transaction is made, it is added to the mempool and a miner will take these transactions from the pool and try to generate a block which contains this transaction. However, before ...
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1answer
26 views

Static difficulty in 1.8.27 for local network

I am having trouble getting geth 1.8.27 to have a static difficulty on a private network. I followed the instructions from here. But when I test it, the difficulty still increases. I tried again, ...
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26 views

How to auto-execute smart contract's function by Aion or other method in the private chain?

I was a little bit confused about Aion scheduling system, because I want to do it on the private chain, in the example https://github.com/ETH-Pantheon/Aion, they have both smart contract Aion and ...
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1answer
19 views

How to connect with Metamask and Smart contract?

I am ready with my frontend design. I have only 3 files HTML, CSS, and JAVASCRIPT. So, I didn't create any project or DAPP to have other files. Now next step is to connect with metamask and smart ...
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1answer
42 views

My Solidity files are not compiling and I am getting constant error

I'm new to blockchain and I'm following a tutorial. However, I'm getting problem compiling my first contract on Truffle. Here's my code : pragma solidity ^ 0.5.2; contract ApprovalContract { ...
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I am sending some ether from account[0] to account[1] using geth console. But the amount is not getting added to the receiving account

I tried to mine the transaction using miner.start() command, still account balance remains the same > miner.start(8) I0428 16:27:15.927553 miner/miner.go:136] Starting mining operation (CPU=8 TOT=...
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43 views

How can I display the data returned from the solidity function?

Here is a js file that will try to get the list of departments entered into the system. I wanted to display all the department's name in a html page. But nothing is displaying. Below code is the js ...
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1answer
39 views

Access deployed smart contract using web3.js

I am new to Etherium smart contracts. I have created a smart contract and deployed it on https://kovan.etherscan.io. Now I am trying to access this contract from node js. below is my code but I am not ...
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25 views

Parity syncing in archive mode stuck at block 4839206

I am running Parity inside docker in pod in Kubernets on Google Cloud. The pod is using disk with 2700 GB for storing Ethereum blockchain, and currently disk has about 2100 GB free. Unfortunately for ...
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1answer
23 views

How to show the time when the blockchain contract called? [duplicate]

I want to show the time when blockchain contract called. I am currently saving the time in the blockchain using a method like this function userCheckIn(uint placeid) public { userCount++; ...
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2answers
64 views

How can the smart contract auto execute the function in the private chain?

I know currently, we can use the Ethereum Alarm Clock and Aion scheduling system to execute the function automatically, but according to what I know, it only can work in Main Net and Test Net(Rposten)....
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1answer
31 views

ganache-cli: how to persist new created accounts

I start my service by: ganache-cli -d --gasPrice 0 -q --db=./db This persists my 10 defaults created accounts, but when I create new accounts using Web3: web3.eth.personal.newAccount('password') ...
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1answer
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Can anyone with part of the chain (e.g. a light node) read unencrypted transaction data?

I need clarification on the fact that "the blockchain is public and anyone can read it". Given a node which is storing only, say, 1 block from the blockchain, can that node read the transaction data ...
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1answer
25 views

Can Qorum Blockchain supports partail transaction encryption?

My use case is that we need to protect sensitive data in the transaction in blockchain. But we want to open other data in the same transaction to the public, Can Quorum support the above mentioned ...