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 authenticate user details in smart contract?

I am building a login system in my dapp for which i have to check the details with already registered users .I tried it by getting user details in frontend and then authenticate it but i think it is ...
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What would be good result measures in Ethereum

I'm thinking of a way to present relevant results measures for my blockchain. I can see how for hyperledger is interesting to present (transactions per second x block size) or (latency x block size). ...
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block syncing current is smaller than starting why?

I'm sync the chain after a power cycle, so current is behind highest for sure, but I also saw that current is falling behind starting block number, how is this possible? starting is the highest on ...
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Creating a system with multiple blockchains where they can interact with one another?

I'm currently trying to create a sort of proof of concept where I would like to create a system of blockchains for individual accounts to track their balances. The idea is to have a snapshot of their ...
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Ethereum Smartcontracts with YottaChain

I am very much curious about this new storage system YottaChain. Can someone point me good articles/videos/sources as a reference to go through and understand its implementation with ethereum smart-...
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What is the best way to store data/information while writing smartcontract?

Smart contracts are immutable. Unless we're 100% sure that our smart-contract is fully functional without any exception we never want to push that in the main net. That's why we have public test net. ...
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How can I make an API that can receive a transaction hash and return the transaction result?

I have a simple gaming contract where users play dice and bet on the result giving the range (1-100) in which the two dice rolls might result to. It has a payable function called call_bet( ) which ...
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Success transaction of Ethereum not reflecting in my coinbase wallet

I transferred ethereum of 0.074 to my coinbase wallet. it is showing success transaction but it is not reflecting in my coinbase wallet, why?
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cannot transfer token from EOA account to a contract from function

i was making a contract for staking where user transfer its token to a contract and i will give him interest but i got stuck to this problem i have been searching for 3-4 days but for it is not ...
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What is the proper way to store timestamp in blockchain?

I am trying to store the timestamp in the blockchain using block.timestamp or now. But that keeps throwing warning as Use of "block.timestamp": "block.timestamp" can be influenced ...
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How can I get a list of all rinkeby nodes? [duplicate]

I'm running a rinkeby node and also want to see other nodes' information. I saw there is a list on https://www.rinkeby.io/#stats for nodes. Is there any other list where I can also have a look at all ...
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How to make this interact with metamask

I've been trying to make my contract be callable by metamask (so a popup will occur telling the user to confirm) but it does not seem to work, heres what I have come up with so far. Can anyone give me ...
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Is it feasible to write a DApp that targets multiple blockchains

This question does not target Ethereum specifically, but I hope you can help me out! If my questions are too specific, I apologize in advance. I'm trying to utilize Blockchain's immutable + provable ...
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Alternative to ganache

can someone please tell me an alternative to Ganache? Tried installing ganache on my laptop and it's not supported. Ganache works on 64 bit computers and mine is 32bit. Is there a way I can go round ...
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Web3 IPC provider connect?

I am using Infura web3 provider to connect etherum but I want to use IPC provider(more secure), How to use IPC provider in ethereum web3.
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Insufficient funds for gas * price + value in Ropsten

I write API for smart contract but its shown error "Insufficient funds for gas * price + value"? My try I have increased my address balance but it's showing the same error. I have changed my ...
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Could not Able to start my genesis block “Fatal: Account unlock with HTTP access is forbidden!”

I am getting some problem while i am trying to mine for my genesis block on my Geth command prompt "Fatal: Account unlock with HTTP access is forbidden!" could anyone please provide me help ...
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Which method is efficient to log data in blockchain? Send an event via smart contract or send data in a transaction without value?

I want to log data in Ethereum block-chain. It is obvious that we can create a smart contract that emits events and retrieve data from it. But is sending a transaction with data but no ETH value (just ...
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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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Insert data whithout overwriting the already stored whit the same address

i'm new to solidity and i'm developing an easy app. This is the contract i'm working on. It's all functioning but i need to: do some sort of function that return me all the array value whit the same ...
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When MetaMask removes the Cancel button for a transaction?

When I start a transaction, MetaMask shows it with Cancel button. When does this Cancel button disappear? Maybe after one confirmation? After N (what is N?) confirmations?
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How do I get the available reserve size for a given token on Kyber and Uniswap(V2)

I am doing arbitration with some measure of success; but I suspect I am running into edge cases where the available reserve size is less than what I am trying to buy or sell. Something like this: ...
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how create address for each ethereum user [duplicate]

I have a group of Ethereum users how do I create an address for each user to send their data on the network?? I want a way to create addresses for each user??
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Blockchain interoperability

i hope that you are doing well! I wanna build an Blockchain interoperability approach based on side chain and i don't know how to start, so if someone can help me please don't hesitate to text me i ...
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Web3- Sending data to Ganache and then loading a new page to retrieve the same data back

JAVASCRIPT const address = '0x2537155193458a51c99d840e3dBc1f60E004aA85'; var contract = new web3.eth.Contract(abi,address); console.log(contract); $('#invoice-btn').click(function(){ contract.methods....
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How to create a multisg account on Geth server?

As you know, multisig wallets are more secure approach in financial cryptocurrency businesses. In my researches, I found out how can I create a multisig wallet in Bitcoin blockchain using this link. ...
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Weird exchange rate when buying DAI with Ether

I wrote code to buy DAI using ETH on Uniswap V2 as follows: function buyCryptoOnUniswap(uint256 etherCost , address cryptoToken) public payable returns(uint256){ //address cryptoToken = ...
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Finality in blockchain consensus

Is Absolute/ Immediate Finality a goal in blockchain consensus or does some areas work better under probabilistic finality such as Ethereum's Pow and to be PoS? (I know that some networks using BFT ...
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How does chainlink solve the oracle problem? [closed]

I've heard a lot about Chainlink recently -- how Synthetix, Aave and other top Defipulse projects are using them. How exactly does Chainlink solve the oracle problem from a technical perspective?
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Why do I need decentralized oracles?

I've been reading a lot about how smart contracts work, and I'm a little new to the area, but why do we need decentralized oracles? It feels like I can just make an API call from wherever and it's OK?
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Is a Hash Function really useful in a Smart Contract Election?

Noob here. Was reading this: https://karl.tech/learning-solidity-part-2-voting/ From my basic understanding, a hash function: Receives an input (like x) and spits some result (like y) y is ...
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BlockNumber stuck on 0 while a private network node is looking for peers

I'm extremely new to Blockchain and mining, and I've followed this tutorial to create my first private blockchain. I am stuck when it comes to mining and I'm afraid I'm quite lost. Afte I've started ...
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how to connect ethereum local provider https://localhost:8545? [closed]

I am using infura web3 provider in ethereum but I don't want to use third party providers in my project so I want to use localhost:8545? how to use this provider? Is it connect to the ethereum node? ...
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Store encrypted data on-chain VS on cloud

So, I am currently doing research for a project and an interesting question was born. If I have data that I want to store encrypted, why to choose blockchain instead of a cloud provider? Since the ...
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Blockchain Consenus Protocols Comparison [closed]

Good day community, I do not know if this is the best place to ask as this is the Ethereum Stack Exchange, if not, please let me know. Thank you. I am currently busy with a Master's Project and really ...
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Hashes of all previous blocks are known but why the hash of block.number-1 is vulnerable and not the remaining 255 blocks?

I have read at different places that blackhash(block.number-1) is vulnerable (to miner's blockhash(block.number-1) vulnerability) because the hash is available but what about the other previous 255 ...
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How can i create my own version of Metamask? (Wallet, provider and a signer)

I have done a lot of research regarding the working of web3 and the new library called ether.js, Also how the seed phase work in the creation of wallet and addresses and the Hierarchical Deterministic ...
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What is the difference between coinbase address and normal address?

i am unable to find the difference between these two addresses. Do coinbase address also change after each transaction?
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What are the odds of getting same address or private-key or 12/24 set of mnemonic to 2 different people

Questions!! What are the chances that 2 people get the same set of those 12 or 24-word mnemonic?? In web3.js, there is a function ' web3.eth.accounts.wallet '... It spits out a set of accounts and ...
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Solidity function calls from javascript work locally but fail on ropsten,kovan etc with Error: Returned values aren't valid, did it run Out of Gas?

I have a smart contract whose function calls works fine when called locally using javascript and ganache. But when I deploy to ropsten and others, the calls to its functions fail with Error: Returned ...
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Proof that a variable is truly random [duplicate]

I have thinking of the wonder that an application could offer if it could prove that some of its data are truly random and so not controlled. Can the ethereum blockchain offer such a service and how ...
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How to speed up ethreum transaction after initiating

Is there any possibility to speed up transaction after creating transaction receipt. My project need to similar functionality we have with metamask is there a way we can accomplish this using any ...
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We need separate hyperledger stack exchange! [closed]

What do you guys say? I think we need a new community so that we don't mix hyperledger and ethereum questions.
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How does NONCE prevent a replay attack in case of knowing NONCE value?

I have a question about a nonce in the Ethereum network. I understand that a nonce helps to prevent a replay attack, but there is one particular part that I don't understand. I have applied my ...
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State only node

Is it possible for the network clients to just keep the latest network state (without keeping track of the past transactions) while not harming the network security? That is, is it really needed to ...
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ParserError: Expected primary expression - address payable - payable()

I'm trying to get myself familiarized with ethereum. So I was going through a repo, and tried to rum the code : function transferFundOnResolve(uint cid) private { // Could also be used: ...
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Any good recommendations on online courses for learning how to build decentralized apps?

There's one called DappUniversity, but wondering if there are any other courses. And where did you learn how to build dapps? Thank you!
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is “newBlockHeaders” in web3 emits a legit block?

I'm using web3.eth.subscribe('newBlockHeaders') to track transaction I sent to the blockchain. My question is that is the block emitted from "newBlockHeaders" legit or in other words, the block has ...
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How can we write the geth cache data on to the disk?

Recently we ran into an issue where all the nodes of our ethereum consortium network are crashed at once, as all are in same data center. In this crash, we lost the cached data of geth and so as a ...
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Which operations can change ethereum address balance?

I am writing a program that would monitor changes in balance of a set of ethereum addresses. I did the same for UTXO based coins, and the logic was pretty simple. All of the changes were directly ...

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