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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Passing a hash value to function
I'm trying to authenticate users by comparing the hashes created by backend server and contract. Seems like "byte32" values cannot be coerced into strings. So, instead I'm converting it into ...
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I have a Transaction Hash, how to get the readable Input Data?
i have a Transaction Hash:
0x9f46760404dd3075533e8360fe4beb0ba7210423af1f4a95a5c80defffe824b5, for
how do i decode the "input data" easily?
for example:
https://www.blockchain.com/eth/tx/...
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Detecting dropped and replaced transactions web3.py
I am using web3.py. Given a transaction hash, is there any way to determine if a transaction was dropped and replaced by another transaction with the same nonce? Currently i am looping w3.eth....
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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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1answer
24 views
web3 eth return returns a nonexistent transaction hash
I'm trying to create transactions something like this:
var sender = meth.eth.accounts.privateKeyToAccount(data.fromPrivate)
meth.sendTransaction({
sender,
to: data.to,
amount: data.value,
}, cb)
...
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1answer
28 views
Data validation using Ethereum
I'm pretty new to the BC and specifically Ethereum world and I'm just starting to scratch the surface of the potential applications of this powerful technology.
As I'm approaching to build my first ...
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1answer
36 views
Mapping didn't storing unique values
I wrote this piece of code with the goal to store unique documents hash. Used mapping to accomplished that.
pragma solidity ^0.5.16;
contract DocumentHash{
string public documentHash;
...
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1answer
21 views
Blockhash Minus-256 Problem [duplicate]
What is meant by Blockhash Minus-256 Problem?
I am reading an article at:
Bad Randomness
It talks about Blockhash Minus-256 problem but does not explain much about it. As a result I can’t ...
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1answer
42 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:
...
2
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1answer
30 views
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
21 views
transfer hash verification on contract side
I want to verify if message-hash has a particular contract method.
Like below web3 code generates a rawTransaction having,messageHash,v, r, s, rawTransaction
let rawTransaction = {
'from': ...
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Advantage of Chainlink's VRF over commitment scheme chain
News
Chainlink announced a randomness oracle via VRF: https://blog.chain.link/verifiable-random-functions-vrf-random-number-generation-rng-feature/.
Question
What is the advantage of an VRF over a ...
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Geth returns tx hash but blockchain
I have a Geth server on light mode, and implemented sending transactions based on web3.php project. Everything works well, except sending transactions.
The code I am using sends from, to, and value ...
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1answer
28 views
web3.eth.getBlock isn't triggered
Basically, i want get the callback result of first method to get each index value in pass it to the second method to scan this value, in this case is an ethereum transaction to get the input value. ...
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1answer
19 views
Sha256 and abi.encode of number
If I calculate the following in Solidity 0.6.3:
bytes memory secretSalt = "abc";
hashedSecret = sha256(abi.encodePacked(secretSalt))
I get the result "...
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1answer
17 views
Is there any other signature mechanism like ECDSA to verify the signed message if its tampered or not?
I would like to know if there are other signature verification methods other than ECDSA, to verify the message (eg., string, number) signed by a signer.
Actually if there are alternative algorithms ...
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Geth returns txhash of sendTransaction() but nothing is broadcasted on Ethereum blockchain
I have a strange issue with Geth. The code I've written is based on web3.php and worked well up to now. Currently, I'm testing sending ETH via sendTransaction() method. The operation finishs and I ...
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1answer
32 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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1answer
24 views
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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2answers
77 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 ...
0
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1answer
28 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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95 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
52 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 ...
0
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0answers
20 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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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
210 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) ) ...
0
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1answer
51 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-...
2
votes
1answer
146 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 = '...
asked Aug 22 '19 at 10:24
Juan Ignacio Pérez Sacristán
2,7633 gold badges27 silver badges60 bronze badges
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2answers
532 views
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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1answer
162 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
57 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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3answers
280 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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1answer
95 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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1answer
65 views
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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1answer
60 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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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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1answer
246 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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3answers
381 views
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
212 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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0answers
21 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
66 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 ...
2
votes
1answer
99 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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vote
1answer
55 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 ...
0
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1answer
59 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
627 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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134 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
680 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 ...
1
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1answer
278 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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1answer
542 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 ...
3
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1answer
67 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 ...
