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 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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2answers
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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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1answer
40 views

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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0answers
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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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1answer
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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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1answer
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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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1answer
60 views

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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2answers
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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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1answer
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Could not find a declaration file for module 'solc''

I have installed solc without any errors or warning, but when i am trying to run node compile.js command in cmd then i am getting following error On checking the code, i found that "const solc = ...
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Any email signIn based blockchain wallet APIs for integrating into web dapps & native dapps (Android, iOS)?

I'm looking for an email SignUp / SignIn based blockchain wallet which provides API for integration into web dapps and native mobile dapps (Android & iOS). During payment routine in dapps, this ...
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1answer
47 views

Blockhash: Register the block number

I am reading the following article from a website: bad randomness In the context of Blockhash the author says: For instance, a good protocol (formulating a random trial as a “bet”) is the following: ...
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Ethereum Logs since Beginning of Time

I can subscribe to all events in ethereum network (logs, pendingTransaction etc) so I can get only newly generated events (while I am subscribed). For my analysis I need to retrieve all logs from ...
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1answer
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DApp examples containing complete source code

can someone provide me some high quality ethereum dapp codebase examples? This should comprise of not only the smart contract codebase but also the app codebase , complete with the front end UI (...
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What is meant by on-chain randomness? What is the difference between on-chain and off-chain operations in the context of randomness?

I want to understand on-chain and off-chain operations in the context of randomness. Kindly provide me an example so that its clear to me. I got one post here: What are offchain and onchain ...
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1answer
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Maximum totalSupply of an ERC-20 token? And is it different for any other ERC specifictiond?

uint256 This storage implies that it should give us a max totalSupply of 2^256 - 1. A HUGE number. Note: I only need to store integers, not fractional values for my application. Is this true? Is ...
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Why does Ethereum use JSON-RPC and not gRPC?

I am fairly new to networking protocols especially JSON-RPC and gRPC as they are not nearly as common in web development as REST. I was reading around and seems like gRPC generally performs better. So ...
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1answer
54 views

How to send an array of structs from web3js to solidity contract?

I am getting an error when passing (javascript array of objects) from web3js, To solidity function that takes (array of structs) as a parameter. could you help me? below is the code and the error /...
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How would a miner include my tokens merged mining function in blocks they mine?

So I have a merged mining token. How would a miner include my function in the blocks they mine? pragma version: v0.4.26+commit.4563c3fc.js Merged mining code: function mineTokenReward() { ...
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Accessing modifier of another smart contract - Role Based Access Control

I am trying to create a simple role based access control system for the contracts I have created. I have two smart contracts, one named Users that stores all of the users details as well as the type ...
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1answer
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How can I implement a custom blockchain?

I am doing a research project which requires me to implement a blockchain with pBFT consensus algorithm. The blockchain would be very simple - A client should be able to send 2 values, the validators ...
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1answer
29 views

Couldn't get any accounts!, Ethereum client is not configured correctly

I'm running testrpc on the default port 7545. I run truffle console and test with: web3.eth.getAccounts().then( function (result) { return result[0] }); This works fine. According to docs the ...
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1answer
101 views

Verifying ERC20 Contract that uses OpenZeppelin's library contracts

I deployed an ERC-20 Token contract and would like to now verify it on etherscan.io My contract utilizes Open-Zeppelin's library of contracts - which means it's importing one of their contracts into ...
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1answer
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How Blockchain system maintenance is done without downtime in real world?

I have a question regarding the maintenance of blockchain system. Whenever any new release comes up then how are the changes made in blockchain without downtime in real world? or is downtime there? I ...
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How to schedule a transaction to a Contract? [duplicate]

I have a simple getter-setter contract. I want to schedule transactions for a method of my contract on a particular date and time. Do we have a function to schedule transactions to a contract in ...
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1answer
18 views

Current State concept in Blockchain

Anybody explains what does this statement means, 'Blockchain is not a snapshot of current state'.
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1answer
24 views

What is the difference between IPDB and Blockchain Databases?

I wanted to know what are the differences between IPFS, interplanetary file system and a block chain database like IPDB and BigChainDB
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1answer
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Isn't the blockchain size going to be a huge problem in the future? [duplicate]

At the moment the blockchain is already quite large. And since the main idea behind the blockchain technology is to get away from services that provide the information and rather have the information ...
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Geth server syncs itself very slow on SSD storage

This is the second time I've lunched a Geth server with full mode on a server with the resources below: 4Core CPU 16GB RAM 400GB SSD But server keeps staying arount half of highestBlock and its ...
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1answer
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Is it possible to initiate Geth server from a specific block instead of genesis block?

I tried setting up Geth servers in full node different times, and all of them are always behind half of total max block. So, they cannot be synced easily even after weeks. I would like to know can I ...
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1answer
25 views

Integer underflow/overflow

What is integer overflow and underflow and how it can be possible? I saw its example that coders avoid this bug by require(balanceOf(_to) +_value >= balanceOf(_to)) where _value is an unsigned ...
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1answer
54 views

API Call in solidity: gas required exceeds allowance (8000029) or always failing transaction

I'm trying to make an API call in solidity. pragma solidity ^0.6.0; import "github.com/smartcontractkit/chainlink/evm-contracts/src/v0.6/ChainlinkClient.sol"; contract GetData is ChainlinkClient { ...
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2answers
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Building a mobile DApp without a full node?

I'm new to blockchain and Ethereum and have a few questions: Does Apple's App Store allow mobile DApps other than wallets and browsers? Is it possible to build a mobile DApp that runs on your mobile ...
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1answer
43 views

Transaction malleability

I read about transaction malleability and have some questions regarding that, please help: It states, for transaction malleability a person changes the signature such that the transaction remains ...
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1answer
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How to structure a contract for future upgrades

Imagine I have a contract I have implemented and deployed like this: pragma solidity ^0.6.0; import "@openzeppelin/contracts/token/ERC721/ERC721.sol"; import "@openzeppelin/contracts/utils/Counters....
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1answer
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Type Error: send and transfer are only available for objects of type “address payable ” not address

pragma solidity ^0.6.0; contract Campaign { Request[] public requests; address public manager; uint public minimumConstribution; mapping(address => bool ) public approvers; ...
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How to duplicate a Geth server?

I have a Geth server which is fully synced, but the second server I have lunched cannot being synced after 2 weeks! I don't know why is this happening, but I decided to test another way. I setup a new ...

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