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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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28 views

Automatic sign of Transaction

Is there any secure solution(without exposing a Private key of the user) to automatically sign transactions, which are requested from a DApp, so that user doesn't have to sign each of them manually? I ...
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27 views

Check when a block is mined

Is it possible to know when a block is mined? Is there any timestamp or event/subscription?
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64 views

Parity node is slow in syncing ethereum Ropsten net

I'm using a parity node for the purpose of checking transactions, address balances and generate new addresses via the RPC interface. I noticed lately that the balance of the addresses are not updated ...
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1answer
20 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. ...
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28 views

Whats a good ETH notary service since BTC based OP_RETRUN txns are taboo?

I want to notarize a SHA256 hash of a document I have. Before ETH I would have used a BTC OP_RETURN transaction service. Since BTC is trying to reduce notary spam, what would be a good ETH notary ...
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7 views

Truffle Console detecting a single key press as multiple key presses

So I have installed truffle using: npm install truffle -g, now when running the truffle console some of the key presses are being detected as two key presses for example, pressing up to load the last ...
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27 views

Is the following scenario doable by a smart contract?

I have 2 persons ( say A or B). They want to have the following agreement. Person ‘A’ specify a deposit (x coins ) for user ‘B’ under a certain condition with a future time lock ‘t’. If user ‘B’ ...
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1answer
18 views

Is it possible to put tax lien certificates on the blockchain?

Tax lien certificates are investment vehicles issued by a county taxing authority secured by unpaid tax liens on property. Is it possible to put these assets onto the blockchain so they can be traded ...
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1answer
24 views

How network hashrate is being calculated? [duplicate]

Hashrate The number of attempts that miner makes per second is known as the hash rate or hash power. Network's hashrate It is the most important data point in blockchain tech. ... Essentially, the ...
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How to pass the function of a parsed ABI to MetaMask?

I am developing a dApp that is parsing an ABI and then it shows the functions of it and fields that is for every function's variable and i want to send the function with its variables to MetaMask to ...
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31 views

How Merkle trees are implemented in a database exactly

I have just checked out these resources: What is a Merkle Tree? Beginner’s Guide to this Blockchain Component Using Merkle trees to detect inconsistencies in data Exploring the use of Hash Trees for ...
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1answer
24 views

How to store and access large amount of data in block chain?

I am trying to implement Role based access control mechanism using block chain. My model consists of two tables(user assignment and role assignment) which contains 500 entries each.So, I can't enter ...
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113 views

How can i implement deadlines in smartContract?

Suppose I am running a gallery and ask participants to submit there paintings before a specific date. After passing that date participant should not be able to submit their entry. How can I implement ...
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66 views

How does the network validate a block in PoS

In general PoS, the forgers stake their coins and then a validator chosen in a pseudorandom fashion gets the chance to validate a block. But how do the whole network validate it? In PoW, for example, ...
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1answer
28 views

ERC223 and ERC827 can receive erc20 tokens and call a function immediately?

As the title says, is that possible? For example on my ico contract, I accept USDT erc20 token and when I receive each transaction, call a function for that and send that address my tokens or eth.
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1answer
33 views

get bytecode in smartcontract ? possible?

is it possbile to get bytecode of already deployed contract on another contract? example : get bytecode of contract A using contract B (using solidity )
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Web3 Contract Constructor Error

Currently getting this error in my Browser's Console: My current set up is as follows: Truffle v5.0.3 (core: 5.0.3) Solidity - 0.5.0 (solc-js) Node v8.9.4 Here's my code - and note that I'm using ....
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2answers
724 views

About contract kill and forensic investigation

Let’s say that I created a contract and, using that, I and other people, made many transactions which meaning is undoubtably proven reading the contract. At a certain point someone kills the contract ...
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33 views

when and who executes the ethereum transaction

Although this question is asked and answered several times, I'm still confused about who executes the ethereum transaction and when? I want to know the right answer (if possible with proof from the ...
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1answer
31 views

How to deploy a dapp which uses multiple blockchain

I am a newbie and started learning dapp on ethereum. Up till now, I wrote smart contracts; created frontend with html, css and js; deployed smart dapp on either private network(geth, ganache) or ...
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25 views

Zero Knowledge Range Proofs

I am new to the world of Zero Knowledge Range Proofs. I read the following on GitHub: https://github.com/ing-bank/zkproofs The Zero Knowledge Range Proof allows the blockchain network to validate ...
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2answers
42 views

Ethereum Enterprise Blockchain

I am starting a project that I need to build a solution to track products (ex: from farm until it gets to the supermarket) Basically, I need to set up a blockchain structure for my company(private) ...
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35 views

Failed to register user “user1”: Error: Calling register endpoint failed with error

i'm going to register a user to hyperledger fabric in linux according to this tutorial but after this command : node registerUser.js i got this error : Failed to register user "user1": Error: ...
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1answer
13 views

What is the authorization for any technical central action in Ethereum system?

When, after fully reviewing, pull requests management and a detailed discussions on github and so on, it arrives the moment in which someone must take into his hands the technical intervention on the ...
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46 views

ERC20 Crowdsale Contract Deployed - but Fails to Sell Tokens

I successfully deployed both an ERC20 Token as well as a Crowdsale Contract to the Ropsten Testnet. -I used code from OpenZeppelin's library for both contracts -While the deployments work and I'm ...
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1answer
15 views

Ethereum Smart Contract with Custom Fee and Percentage of the collected Fee Distrusted token holder

I wanted to know is there a possibility to create a smart contract for a token wherein the transaction fee could be overridden with the network fee and the fee collected on the transaction can be ...
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3answers
64 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 ...
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29 views

IoT solution for blockchain

I would like to experiment with an integration with Iot and blockchain. My idea is to save a pair of keys (privKey, pubKey) inside an IoT device in order to sign the transactions and send them to a ...
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1answer
213 views

Why does solidity check only the first 4 bytes of the calldata to determine the method?

I was doing research on EVM and solidity and I came across this fact that the calldata/input data is created using RLP encoding and stuff. I know the process and I don't want to elaborate on that. My ...
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1answer
35 views

timed commitment using ethereum blockchain

I read this paper: https://eprint.iacr.org/2013/784.pdf that introduces the idea of Bitcoin-based time commitment scheme. In which if the commiter does not open his commitment before a specific time ...
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1answer
33 views

Transferring funds from a contract to an account using adresses

I had been trying for a long to transfer the complete fund with one of my contracts to a specific account. But nothing seems to be working. pragma solidity >= 0.4.22; contract reg{ address ...
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1answer
40 views

Execute smart contract only if the wallet contains some tokens [closed]

i created an erc20 token and i'm trying to create a smart contract that stores some informations in a blockchain just if the wallet contain my tokens. How can i do this? Have i to work on the token ...
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1answer
39 views

How do we extract the content of a hash manifest generated by swarm after a download?

As far I know, whenever we upload a file or a directory using: swarm up File we get back a hash that is the manifest containing the uploaded file. However, I am not sure I do understand how to ...
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1answer
28 views

How Ethereum stores its data in the blockchain [duplicate]

I am new to ethereum and the blockchain, but I am wondering about blockchain databases. Mainly I am wondering how exactly the database data and the blockchain merge. For instance, in a database you ...
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1answer
46 views

The geth account new and web3.eth.accounts.create

The geth account new and web3.eth.accounts.create. That both function/command are same are different.To create new account.
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1answer
21 views

Is there multiple chains of block in ethereum network?

Since blockchain is a chain of blocks, In ethereum, 1. is there only one chain of blocks 2. are there multiple chains of blocks.
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1answer
20 views

How does number of miners impact in processing the business logic(smart contract) in Blockchains

Does a number of validating devices/miners have an impact on processing business logic? If I understand correctly, as the number of validating devices increases, the time it takes to reach the ...
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2answers
34 views

Saving the actual data vs. hash of the data - which one is better?

I am new to etheruem, I would like to create a smart contract for keeping document data. From 2 designs below, can I know the pro and con of each one, please? put the array of raw JSON data to the ...
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What filesystem should I use for geth and leveldb?

I used old LGA775 machine for running geth node. Its mobo has older sata 3gb/s (benchmark showed that ssd bottlenecked there) and only 4gb of DDR2, with windows installed. So syncing is a real pain ...
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1answer
13 views

Is it possible to provide some manual data to create private key for the ethereum account?

We were trying to provide some manual data to create the private key if I want to create a new ethereum account using this private key.
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3answers
112 views

How to store private data on blockchain to be readable from a contract?

I'm writting DApp on Ethereum (Solidity) and I need to find a solution how to store a private data on blockchain, when I also need to proceed them somehow. If it is only about storing, I can use some ...
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1answer
26 views

Questions about blockchain

I am a newbie with blockchain and I have a few questions please, I've already googled but I have misunderstood some points: How data is stored in the block in blockchain? in bit format, text or other?...
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1answer
51 views

How to return the struct data

How to return the struct data struct Transaction { address from; address payable to; uint amount; } I am returning like this function transactionDetails() external view returns(...
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1answer
76 views

Does the ethereum ecosystem exist out of one or multiple blockchains?

Most of my knowledge is based on BTC which doesn't have the concept of (ERC-20) 'Tokens' so I have a question related to that: Does the Ethereum 'ecosystem' with its hundreds or even thousands of ...
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1answer
36 views

How an Ethereum Node stores data?

How an Ethereum client stores the blockchain data in the disk? I know two of the major Ethereum clients is go-ethereum and parity, so I'm also asking if they store data in a different way or if there ...
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1answer
23 views

Can anyone please help me how can I start with blockchain testing,Deploy application and testing app [closed]

I am completely new to blockchain testing.Can someone please help me with how can I start with blockchain testing and procedure from where I should start and material for the same if possible.
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1answer
116 views

How secured are private data stored on blockchain?

I'm quite new in Ethereum world and I'm still little bit confused about this: If I store any data on blockchain, is it readable from anyone? Let's say I have this is Solidity: ... string private ...
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1answer
24 views

is data structures necessary for a blockchain developer?

I want to know if i had to study data structures and algorithms for being a blockchain developer or a smart contract developer
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42 views

Transaction submitted through Infura, but not from local node

So, I have a Rinkeby fast sync on my server. When I try to interact with my contract and transfer something, geth says "Submitted transaction", but then I can't find it using its hash on etherscan. ...
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1answer
19 views

part of private blockchain disapear

I have a private blockchain, mined by one ec2 instance. When I restart the instance, significant part of the chain disappear with all transaction and contracts on it. How can I prevent this?