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.

Filter by
Sorted by
Tagged with
0
votes
1answer
16 views

Gas required exceeds allowance truffle migrate

Hi i am trying to work truffle migrate and firstly it start to Migration.sol and then Election.sol. When start to deploy ELection.sol it throws following error. What should i write gas:270000 instead ...
3
votes
1answer
55 views

MetaMask blocks Web3 requests

I just set up a Block Explorer to interact with my private blockchain. The private Blockchain runs in a VM. The host system connects to the Block explorer (also on VM). When I have meta mask ...
4
votes
1answer
411 views

Storing private data off-chain with a sharing feature upon request

My question is not very technical from an implementation point of view, but I am looking for advice to achieve a specific use case using blockchain tech. I would greatly appreciate any insights or ...
0
votes
2answers
1k views

What are the popular API to get current exchange rates for Ethereum to USD

Can you please list all the API providers for cryptocurrency to USD Thanks in advance.
1
vote
0answers
26 views

Returned value arent valid did it run out of gas?

After migration command line (truffle migrate --reset --network rinkeby), it is deploy. However i couldnt see at etherscan website when i enter the contract address. Should i see? Whatever then i ...
0
votes
1answer
36 views

Load Smartcontract in Nodejs

I created the server based on golang. This server can load smart contract that is deployed using its address. It works on my local machine, but it does not work on EC2 instance. So I decided to ...
13
votes
8answers
716 views

Would it be profitable enough to do a Master's degree in blockchain technologies (focused on ethereum above all)?

The end of my university studies is getting closer and closer. I'm sure I want to do a Masters degree, but I have some doubts. About a month ago my university released a Masters degree completely on ...
4
votes
1answer
678 views

Call write function, which doesn't change contract value

I'm new in smart contracts and faced with one problem. After deploying contract to my test local blockchain network, i try to set new value via setter, after that I call get method of contract and it ...
0
votes
1answer
18 views

Truffle migration takes too much time and dont migrate

0 Hi i am trying to migrate contract by using getch on oracle virtual box ubuntu. Although 1_initial_migration.js deploying it shows Block: 0 Seconds:16743 and it is not completed to deploy and also ...
0
votes
1answer
22 views

Are the timestamps of blocks for Ethereum only accepted when they are monotonically increasing?

Are the timestamps of blocks for Ethereum only accepted when they are monotonically increasing? If yes, why? And why other blockchains like Bitcoin and other blockchains with shorter block time can ...
0
votes
1answer
56 views

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 ...
3
votes
1answer
819 views

web3.min.js is missing in ./node_modules/web3/dist

I am following the below tutorial to create implement blockchain using web3. https://medium.com/coinmonks/interacting-with-ethereum-smart-contracts-through-web3-js-e0efad17977 When I am using npm ...
0
votes
2answers
63 views

Contract's transaction count in a certain period

I want to determine the number of transactions of a contract in a certain period. My question is that in the transaction receipt, if we want to say that contract A has x number of transactions will ...
0
votes
0answers
8 views

How can I find the block where a user enacted a certain event on a contract?

I'm trying to build a web3.py program to take in a given user's address, and return the amount of ETH traded since they added liquidity to a Uniswap exchange. Uniswap is a smart contract on the ...
2
votes
1answer
18 views

Etherescan Unique Address Growth Chart - How is it computed?

how does Etherscan get this information from the blockchain? Is it possible via using a web3 module? Any insight? https://etherscan.io/chart/address
0
votes
1answer
778 views

Ethereum Pending Transaction

I am trying to send 2 transactions. eth.sendTransaction({from: eth.accounts[0], to: eth.accounts[1], value: web3.toWei(5, "ether")}) eth.sendTransaction({from: eth.accounts[0], to: eth....
23
votes
3answers
11k views

Is it possible to cancel a transaction?

Is it possible to cancel a transaction broadcast to the blockchain? Suppose I broadcast a transaction and want to cancel it before it has been mined. Is this possible? This could be useful on ...
0
votes
2answers
393 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 ...
0
votes
2answers
22 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 ...
0
votes
1answer
18 views

can't get struct in return

I am trying to execute unit tests for a solidity smart contract: I have: mapping (bytes16=>Device) public Device_Table struct Device { bytes16 UUID; bytes16 hardware_UUID; string ...
0
votes
1answer
18 views

Why am I getting a Parse Error in my smart contract after the constructor?

I'm writing a token sale smart contract & my original error was my function had the same name as the contract and I changed it to a constructor because the contract cant have the same name as the ...
0
votes
1answer
27 views

Is there any website for provide APIs for making transaction to different blockchain such as Ethereum, Litecoin, BTC, Neo etc

I want build a wallet which manages multiple coins and I'm looking for a website which provides APIs for transacting to different blockchains.
0
votes
1answer
321 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 ...
41
votes
4answers
19k views

What exactly is an Ethereum client and what clients are there?

Ethereum.org's introductory Command Line Interface tutorial mentions these clients: eth - a C++ client suitable for mining, IoT and contract development geth - a security audited Go client for use ...
0
votes
1answer
20 views

Code:const web3 = new Web3(window.web3.currentProvider) Error: window.web3 is undefined

I am going to connect my contract with the website.However,there was something wrong with the web3? I'm not sure. import Web3 from "web3"; const web3 = new Web3(window.web3.currentProvider); const ...
1
vote
1answer
36 views

Is there any way that smart contract can access xacml policies?

I am trying to implement role based access control model using blockchain. How do i store these policies? Later my smartcontract should be able to allow or deny the rquest of user based on policie. ...
0
votes
1answer
40 views

How can Ethereum be used to prevent fake art sales?

According to this article, some very expensive art pieces are going to be auctioned, and "the auction will be conducted on the Ethereum blockchain. A smart contract will determine the final price for ...
3
votes
2answers
1k views

Error: gas required exceeds allowance or always failing transaction upon function execution

Problem The transaction fails because the transaction ran out of gas instead of it failing because the require condition was not met. It works fine before the solidity update to version 0.4.24. It ...
1
vote
1answer
260 views

Access to a private blockchain controlled by one entity

How can I be the unique authority that can grant access to my private blockchain to only my users and forbid that users to grant access to others?
1
vote
2answers
44 views

accessing unpredictable numbers

I see that this has been a widely discussed topic in the past but I still don't understand why the future block hashes shouldn't be used for lottery-type games. As long as the incentive for a miner to ...
0
votes
2answers
20 views

Why is a failed transaction included in the blockchain as a “failed transaction”

According to this highest upvoted answer, "but still include it in the blockchain as a "failed transaction"... What is meant by the term "gas"?
0
votes
1answer
11 views

Which Protocol is suitable if I want a validated person to authenticate the block?

I want to create a system in which Every user will have some specific authorities. Like Examination will validate the block containnig Student Marks. Finance should have authority to add block ...
1
vote
1answer
20 views

How to do the Smart Contract Storage Migration using Quorum?

I wrote one smart contract without upgradable logic, now I want to update the same smart contract with some changes. Is it possible to copy the data from old contract storage to a new one?
0
votes
1answer
45 views

totalSupply doesn't pass test

I'm starting programming. I wanted to do my first contract and I assigned totalSupply to 1000000. pragma solidity ^0.5.8; /** * The DappToken contract Constructor Set the total number of tokens ...
2
votes
1answer
43 views

node cannot be made up in private blockchain by using command line

I have created the genesis.json The genesis json content is { "config": { "chainId": 46860, "homesteadBlock": 1, "eip150Block": 2, "eip150Hash": "...
1
vote
0answers
15 views

How to Read Construction information?? (from blockchain develpment with go)

pragma solidity ^0.5.10; contract Simple{ uint256 data; string male; string name; string id; function getdata() view public returns(uint256) { return data; } ...
1
vote
2answers
39 views

Can anybody Point out the Difference between Web3.eth.sendTransaction and web3.eth.signTransaction?

Do we need to sign the transaction by web3.eth.signTransaction after initiating transaction via web3.eth.sendTransaction. for example: when I do: web3.eth.sendTransaction({ from: accs[0], ...
0
votes
3answers
105 views

how to store some private data on ethereum blockchain?

The idea is to create decentralized system that stores network data privately with random algorithm on the blockchain . This means only smart contract have access to view data and encrypt it ...
1
vote
1answer
18 views

“The bigger the block size, the greater the computational power needed to mine a block” Does this make sense?

I was going through one of the papers and the authors in the paper mentioned this statement. I am not able to find the correlation as such. I do understand that Larger blocks may propagate slower ...
0
votes
1answer
22 views

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 ...
4
votes
1answer
285 views

Why does geth -light start importing block headers from 3297471

I've been using geth to download the blockchain (on full) and one of the requirements for my research involves the use of light clients. I used 2 computers to download the blockchain on the -light ...
0
votes
1answer
29 views

Create multiple tokens for a unique property

here is the idea: we assign a set of unique tokens to a company and then we allow people to buy some tokens and get partial ownership of that company. How can I achieve this? I was thinking of ...
0
votes
1answer
239 views

Ethereum mist wallet not synchronising, not showing Ethereum and folder

I am a beginner at setting this up and I used a youtube tutorial to download Mist. The problem is it's not syncing the blockchains. I've tried to debug this by going to users/appdata and inside the ...
0
votes
2answers
35 views

How smart contract different than programs-package?

I was reading about the smart contract and I'm able to create the smart contract but I didn't know why the smart contract is used? When I did search on google about this, I understood following - ...
0
votes
1answer
52 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[...
0
votes
0answers
20 views

Error: Keystore: Must include seedPhrase in createVault inputs. How to fix?

i'm studying blockchain development, and i'm trying to create wallet with seed words using eth-lightwallet and vuejs. But i receive this error: Keystore: Must include seedPhrase in createVault inputs, ...
0
votes
0answers
22 views

How to copy the data from a running private network to another

I have two seperately running private ethereum networks,i want to copy the data from the first private network to the second one without stopping.I have tried multiple ways but was not successful.I ...
3
votes
1answer
185 views

Uncle blocks in Parity PoA blockchain

As I know that there is no competition for mining new blocks in POA blockchain as each node mines new block at its given time slot. I have a parity PoA blockchain setup with 5 nodes. While examining ...
0
votes
2answers
32 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 ...
0
votes
1answer
38 views

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 ...