Questions tagged [hash]

A hash function is an algorithm that transfers data input of any size into a fixed size data which acts as a kind of "signature" for the data provided.

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25 views

How can I convert an element of a byte32 array to number?

The array contains an SHA256 hash. I want to add up 2 hexadecimal values, and later multiply them by 1.125 (only keeping integer). The resulted number would represent an alphanumerical character, it ...
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How keccak hashing and for loop happening in pure function?

I put a keccak hashing inside pure function, it works and return me the result.It also works in a for loop. I studied that hashing the data and loop consumes consider amount of gas. Do we need to ...
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32 views

Get hash transaction by your encode input data

In my application i must follow the use case: I need to record any document hash on the Ropsten (eth testnet) blockchain. The hash is unique and i'm using a mapping in my smart contract to accomplish ...
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19 views

Integrity of old blocks in the blockchain

I am learning Ethereum using Geth, and I am testing PoA-Clique networks. Now I have a conceptual doubt about old blocks integrity. Suppose I have a private blockchain network of only one miner node ...
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34 views

Efficient way to save and retrieve hash in blockchain

I am learning Ethereum using Geth. I have a private blockchain and I am saving hashes through a REST API (python web service). I have readed I can save hash values using maps (mapping data type) and ...
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2answers
38 views

From ENS Name to hash AND print in console

I'm just studying about Ethereum, ENS and and and.. Actually I try to compute an ENS .eth Name to a hash. In https://app.ens.domains/name I baught a ENS .eth Name with the Ropsten Testnetwork. Now I ...
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17 views

Blackjack - keep dealer second card hidden

I am working on a multiplayer blackjack implementation with an array of 52 cards as the deck that have a flag if they're selected or not. I'm implementing a random number generator to choose a random ...
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30 views

Can you verify transaction data by matching it to the transaction hash

TlDr; Can you use the transaction hash to confirm the integrity of the data components of a transaction (post data, addresses, nonce, etc). In my application, I have a connection to the Ethereum ...
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2answers
120 views

Gas cost of a sha256 hash

I'm confused about the cost of the sha256 function, because my understanding of the cost from the yellow paper ( https://ethereum.github.io/yellowpaper/paper.pdf (Appendix E. Precompiled Contracts) ) ...
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1answer
40 views

How to parse ecrecover parameters?

I am looking into getting the public key from ANY ethereum address (not owned by me) that has sent a transaction at least once. It seems that the most viable solution here would be to use ethereumjs-...
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1answer
94 views

Different outputs for Keccak256(), which one is right?

To get a value from contract storage I used this geth code succesfully: var contractAddress = '0x88e726de6cbadc47159c6ccd4f7868ae7a037730' var index = '...
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How to cancel pending transaction of ethereum from exchange wallet? [duplicate]

How to cancel pending transaction of ethereum from exchange wallet? It is pending for around 36 hours now. There is no available tx hash.
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118 views

Solidity: extract data from signed message?

In an effort to reduce gas costs for users, I'm looking for a way to delegate certain transactions to a contract owner so that the owner makes a transactions that would have been otherwise sent by the ...
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1answer
53 views

Off-chain authorization system

I'm working on a dapp and am running into a dilemma regarding how to balance trustlessness with the cost of transactions for users. In order to reduce gas usage by users, I want to be able to able to ...
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199 views

How to generate the full list of function selectors for a contract?

A contract has many functions and how to automatically generate the full selector list, including inherited functions, for the whole contract? Preferred solution shouldn’t require more than a web ...
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68 views

How to find the value of erc20 token sent out using transaction hash

How can i find the value of erc20 token in a transaction using the hash generated? I can't seem to find answers anywhere. Edit:I found that it is possible to use w.eth.getTransactionReceipt('...
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is it possible to use IPFS Hash to ensure file integrity?

My question is if i can use the IPFS Reference/Hash to ensure file integrity. In other words if i have a file can i use a specific Hashfunction to ensure that the generated Hash of that file is equal ...
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37 views

What is the best way to store a hexadecimal value in an array in Solidity?

I am attempting to store a hash (web3.sha3) into an array in a smart contract. What is the best way to do that?
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1answer
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Am I hashing the data in the file itself, or just the reference?

I am attempting to create an app where I upload a file to a website and then I submit a hash of that file onto Ethereum. I am unsure whether I am hashing the actual file below or just the reference to ...
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189 views

How to hash multiple values including array keccak256 Solidity v5.0.x and web3 'Autodetection of array types is not supported.'

How can I receive the same hash in solidity and web3? Multiple values where one is a multi dimensional array. Solidity v0.5.x: pragma solidity 0.5.6; pragma experimental ABIEncoderV2; contract Hash{...
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web3.eth.sendSignedTransaction executed successfully but never any ETH transferred actually

as you see in below, i the raw transaction has been set by the gas simplify value, the returned value is an implemented transaction hashcode, but never assumed result by this transaction figure out ...
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1answer
147 views

Getting the transaction hash on function call

I am new to Solidity, Web3, and Ethereum. I am trying to build a web application through which users can upload a file to IPFS, then store the IPFS hash in the blockchain. I am using the React truffle ...
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19 views

Parity synced at not existing block 4839212

I have problem with parity, cant get synchronization in archive mode to end, anything, changing arguments, max-, min-, snapshot-peers, parity verisions do not help. I have blockchain in archive mode ...
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1answer
55 views

Hash bytes32 and uint32 in Soldiity 0.5.8

How can we efficiently calculate a hash value for a combination of bytes32 and integer value? Like in JavaScript "someString" + someInt. I tried: function fx(bytes32 _left, uint32 _right) public ...
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1answer
60 views

How to retrieve transaction hash value from the Promise object using web3js?

I'm trying to retrieve the transaction hash value after I call my smart contract method. My Promise object looks like below. returnPromise: Promise { "pending" } ​ <state>: "...
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1answer
50 views

How to encode function call in C

I understand web3 can be basically used for every existing task, however, is there anything we can use for C? My C program is communicating with the RPC server using the curl library, by posting JSON ...
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1answer
53 views

Costs/efficiency of locating stored data on Ethereum

Based on the answer to this question, storing IPFS hashes on Ethereum could be done in 3 ways: Store it as a string Store it as a struct Store it in event log Ordered from most expensive to least ...
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1answer
471 views

Ideal way to store hash on the ethereum blockchain

I would like to store a certificate on the blockchain. I only need to store its hash and if its been verified by both parties or not. Should I create a struct that is made up of bytes32 for the hash, ...
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120 views

How does a message signed in Remix IDE?

What is signing method that is used in remix IDE and how is the hash value calculated from the message that is being signed?
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1answer
548 views

Block header hash calculation [duplicate]

What inputs go into the RLP and Keccak function to calculate the block header hash? I looked up the header struct. Which of those values are fed into the RLP, Keccak? Were nonce and mixed hash left ...
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1answer
231 views

block hash from block-header rlp [duplicate]

Given the RLP of a block header, how do i get the block hash? https://github.com/ethereum/go-ethereum/blob/master/core/types/block.go#L99 The above link says: Hash returns the block hash of the ...
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455 views

block-header hash verification

As part of a validation service I am working on, I need to be able to verify that the blockHeader hash was created correctly. Based on my understanding following are the steps to regenerate the header ...
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1answer
55 views

How to create and compare a 32 byte hash of a string in solidity 0.5

I simply want to create a 32 byte hash of a string and compare equality to another one, but this is proving almost impossible for some reason. E.g: hash("a") == hash("b") My compiler throws errors ...
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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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i want to get data from the transaction hash i tried many codes at last i am getting boxes in the output

1) First, I got the input console.log(web3.eth.getTransaction('0x725fc75264726f409793164e336e7d5ed35df8d2be469a0cc1a3a8cc4756b9b9').then((i) => console.log(i) )); 2) I manually pasted the input ...
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1answer
99 views

Match web3py hashing function to solidity hashing function

If I am using web3py to hash some data, like so, msgHash = w3.soliditySha3(['bytes32','bytes32'], [dataBytes, saltBytes]); What would be the correct way to hash inside of a Solidity contract and ...
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34 views

For Recipient how do I store Sender's account address and Password of Recipient's own account in hashed from?

How to check following things using Solidity: Password matching (hash formed) if password matches then transfer take place
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81 views

Can I use an address value in such a hash function

I have a method which updates 3 mappings in my contract. To save data I use some items properties and message sender address, which allows easily to get users data. mapping(bytes32 => uint256) ...
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1answer
157 views

How do I use SoliditySha3 in Nethereum?

According to this, web3 should contain the function soliditySha3. It can take an object (JSON), serialize it, and use the result as input to Keccak256. According to the documentation, the arguments ...
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1answer
128 views

Hash functions soldity to python

In Solidity, I run the following code: function hashTest() public returns(bytes32,bytes32,bytes32) { bytes32 _solution = 0xbc756c25d68ea2f260ea5f15e1e1c734c019cbc014270dd386eacca4699f60f6; bytes32 v ...
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1answer
40 views

How will Proof of Stake affect blockhash generation

When (and if) Ethereum switches to proof of stake, how will the hash of blocks (most likely) be set?
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Does web3 soliditySha3 work with json object?

The above hash data is generated by web3 soliditySha3 with the objects below. It seems the function generates hashes as I wanted; each object has different hash value. But I am not sure if it's ...
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85 views

Can we use Ethereum Swarm to store normal data other than blockchain or dapp data.

I want some basic data to be stored like name and city phone no etc.So just want to ask can I use ethereum swarm just to store file and make several node to create decentralized storage.
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813 views

Encrypt data using public key

I have three data fields in a form which will return a string. I would like to hash the value of these three strings and store it in the blockchain. However the data in these three strings is ...
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1answer
201 views

get same output as solidity SHA256 in JS

Is there a js function/library which gives same output as sha256 in solidity? I am saving a hash in a mapping and can access it via cli (truffle console) and see what the hash is but I would like to ...
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1answer
142 views

Is data inputted as a parameter for a smart contract function visible?

Let's say I have something like this: bytes32 person; function registerPerson(address _person) public { bytes32 x; x = sha256(abi.encodePacked(_person)); person = x; } For privacy reasons, ...
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69 views

Hashing header “offline” python

I am trying to prove that the TransactionsRoot and the ReceiptsRoot do belong to a specific block. So that I can verify without web3 that all the transactions and receipts actually belong to this ...
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1answer
35 views

How to get two points (x, y) from an encoded pubkey?

this gives a valid address from two points; address(uint256(keccak256(abi.encodePacked(point[0], point[1]))) & 0x00FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF); but does that mean that if you are ...
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546 views

Creating hash of a struct in Solidity and JavaScript

I have created a message hash in JavaScript using: let message = { 'message': 'Receiver closing signature', 'sender': sender, 'balance': value }; message = web3.utils.toHex(...
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1answer
31 views

Creating an Ethereum id Hash

I'm trying to understand how to convert my transaction data into the id hash before signing the transaction. Let's say I have this data: transaction = { 'to': to_address, 'from': ...