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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In Ethereum, is it possible for a malicious client to duplicate a coin by double executing a transaction?

Is it possible a scenario in which a malicious client executes two transactions with the same nonce of a specific account and copies and sends coins? Suppose users A, B, and C have the following ...
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Conceptual Question: What is the point of making an auction decentralized?

I understand how a blockchain works, I know the pro/cons between a centralized vs decentralized system. My question is specifically tied to auctions (eg: ascending auctions): what advantages would be ...
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Why is no block created for this function? [duplicate]

I have this contract and I've deployed it to ganache pragma solidity >= 0.5.0; contract HelloWorld { string public payload; function setPayload(string memory content) public { ...
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Deploying Smart Contract to Rinkeby

I'm getting the following error when I try to deploy my smart contract to Rinkeby using Truffle: Error: Unknown arguments format passed to new HDWalletProvider. Please check your configuration and try ...
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Storing Struct inside an array. Help Please

I am designing an EHR System that will store patient records (with a unique ID) and separated by the date and Hospital entered. I am able to enter data in Hospital struct mapping to the Record struct, ...
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Can I have some feedback for my blockchain festival idea? Please [closed]

I came up with this idea for a blockchain style festival which runs on Ethereum. I know there are already blockchain festivals but I wanted to know what you think of my idea and if you have any tips ...
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how to get list of transactions history about specific contract address using web3?

I really don't know how to get a list of transactions history about specific contract address using web3.py and I use Infura HTTPProvider I just have only one 'contract address'. Can i get information ...
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How do two parties verify a transaction initially?

Sorry for the beginner question. Im trying to understand how a blockchain transaction is initially verified by both parties. I think I understand the process of externally verifying a transaction but ...
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where is receipt tree stored?

Simple question. I know that state trie is stored in each node's drive. but they are not stored on actual state. Question 1) What about receipt tree ? do they get stored separately too from the chain ...
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in which currency does state trie's balance is stored?

My question is very simple and I couldn't find the answer for it. There's a state trie in ethereum. Each state trie has address as key and value as an object which has balance as one of the keys. I am ...
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How do you handle a chain re-org with contract events?

Given that events are fired whenever a transaction is included in a newly mined block, how do you handle the situation when the mined block containing the transaction gets orphaned? Say I have a ...
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Broadcast transactions to specific miners?

Is it possible to broadcast transactions specific or a small number of miners? I believe there is a concept of private transactions, as used to mitigate front running to rescue vulnerable funds for ...
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Only see the last item of struct using for loop in web3.js

I don't understand what mistake I did in my code. I created a folder before and I was successfully see the correct result of smart contract. For more clarify , Actually I want to see the struct result ...
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What are the required platform to make mobile app that has dapp features?

I recently went over dapp with ethereum block chain but most of the coureses and documentation follows example in webApps. I want to know what are the possible frameworks/library, technology/ ...
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Free transaction on a private ethereum blockchain

I have developed a Dapp powered by Ethereum with truffle. And I want to deploy it on a private blockchain. But I have one question to ask before that. My question is: can I make in sort that my Dapp ...
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Docker unable to connect [closed]

My test-network is unable to connect to the docker files where as I've properly installed the docker and the docker-compose files. Docker version - 19.03.13, build 4484c46d9d Docker-compose version - ...
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Transaction Error. Exception thrown in contract code. REVERT

I keep getting an error when trying to call function "setTokenAddress(address input)" Here's my contract code: pragma solidity 0.6.12; library SafeMath { function add(uint256 a, ...
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Updating ERC-721 Token's Metadata after it was Minted

Is it possible to somehow update an existing ERC-721 Token's MetaData after it was already minted? Let's say we've created a Knight character for a game - by minting an NFT for it, and 3 months later ...
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how does casper help with finality?

My question is very simple... I've watched some videos and read articles, but couldn't figure this. It's said that on the internet If the block has been finalized, it can't be reverted/changed in ...
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Problem In Getting Rinkeby Test Ethers

I tried to get rinkeby ethers from https://faucet.rinkeby.io/ by creating a tweet but the website shows "insufficient funds for gas * price + value” error. I also tried the website faucets....
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Fail with error 'TransferHelper: TRANSFER_FROM_FAILED' By calling UniswapV2Router02 swapExactTokensForETH

I am trying to call UniswapV2Router02 swapExactTokensForETH function on my Solidity Contract. I got Fail with error 'TransferHelper: TRANSFER_FROM_FAILED' on etherscan. this is transaction url : ...
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How to represent specific validated transactional data [closed]

I will use an analogy to express my question: Let's assume some kid is willing to do some chores in his neighbourhood against a certain amount of ETH. He found neighbours willing to engage in such a ...
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How to see the miner account that earned gas? Or how to know the account where gas goes?

I made a transaction to another account on rinkeby and then saw the record on Etherscan. There is Txn fee as gas. But how can I know where the gas went. I mean the account that gas was paid to. I ...
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Cryptographic hash of the entire Ethereum database

I need a cryptographic hash of the entire Ethereum database (of the information in all blocks up to a certain block number). Is there a service that calculates this hash?
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ERC-2309 Minting Multiple ERC-721 Tokens in one Transaction

Anyone know how to work with ERC-2309? It's an extension to the ERC-721 Token standard and it's supposed to make it possible to mint a large number of ERC-721 tokens (meaning 100's or even 1000's of ...
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Is Ethereum blockchain really temper proof or immutable?

Suppose there is a user A which transfers some ethers to user B through a proper transaction. So is it possible to alter the transaction. Something like going back to the block which contains the ...
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It's 2020 September. How big is the Ethereum blockchain when download a full node?

If I want to support ethereum with a full node. How much space do I need to host a full node as of today 2020 September?
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how miners within a mining pool execute transactions and verify blocks?

I know that solo miners have to select & execute transactions in a block and also verify the recipint block and its transactions, all by themself. However, I am not sure how this works in a mining ...
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Blockchain without cryptocurrency

I am new to blockchain and am having certain doubts. Can we substitute cryptocurrency to carry out blockchain operations in any way ? Actually what i feel is that the volatility in cryptocurrencies ...
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solidity equivalent for new thread

I want to create a contract, which has a deposit function. But I also want, in the constructor, to start a "thread" that polls an external data source (via oraclize/chainlink or similar) at ...
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What is the best practice to receive ether from external accounts?

I want to create a smart contract that receive ether from external accounts and pay them some profits monthly. I need to receive ether from them. What is the best practice in this regard? Whether the ...
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How to implement recurrent smart contract without third-party libraries? [closed]

I want to implement an investment service based on ethereum smart contracts in which customers receive dividends four times in a month. For example, a customer receives dividends on 8th, 16th, 21th, ...
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Can I stop geth when it is halfway done and restart it without loosing all the first half of data?

I have started geth (fresh install) using this command: geth --datadir "my/path" I'm halfway done with sync and would like to restart my PC. Will I loose all the data accumulated so far or ...
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How to show token balance from a ETH address in my Android App?

I have an Android App and I want to show the balance of an especific token of the user wallet Address IE: show how many CHAINLINK are holding the user on his wallet Thanks in advance
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Ethereum geth mainnet blocked on “Looking for peers”

I installed Geth for setup a ethereum node on my linux server and use it on my RPC API. The problem is, Geth is posting "Looking for peers" forever, I don't really understand why. This is ...
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Decentralized Identifier - DID method Registration

I am trying to register a new DID method like 'DID:mymethod' for my specific use cases. I am planning to register this new method under the Ethereum Blockchain. But, I am not sure who do I approach ...
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Does more miners mean lower gas prices?

I hope the question is self explanatory but, basically I wonder if the Ethereum code is made in a way that id there is more miners, would that in turn allow for lower gas prices or transactions to be ...
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What is difference between “network hash rate” and “individual hash rate”

suppose for example if nonce is 32 bit then the total possibility of hashing attempts is 2^32 ( 4,294,967,296 ) times only, but why it is mentioned in every article as PH/s or EH/s (1,000,000,000,000,...
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openethereum node disk usage

Using openethereum to sync the eth blockchain, after synced and now the disk space keeps growing 20G per day. The .log file in the db folder keeps growing. After restarting the node, the space will be ...
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truffle init function is showing an error on my Ubuntu 18.04 system

When I execute the truffle init command on my command line(Ubuntu 18.04) it's showing me the following error. ubuntu@ubuntu-vbox:~/block_chain/Ballot1$ truffle init Downloading... Error: Truffle Box ...
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Gas estimation failed error:Can someone help me to resolve this error,Many thanks

I'am facing this error:gas estimation failed:"gas estimation errored with a following message .the transaction execution will likely fail.do u want to force sending?gas required exceeds allowance(...
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How many parallel read/write request single contract can handle each second

I need this reply for a large user base prospective, where each second too many request going to that particular contract , so the question is what is write per second limit and what is read per ...
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blockchain sync failed and stuck

My machine was crashed and rebooted, but after rebooting, geth sync repeatedly failed at a block, I checked the block number, hash is right though, what should I do? INFO [08-08|09:54:23.184] ...
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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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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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