Questions tagged [blockchain]

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The contract is supposed to be private but every node can access the ledger

I am trying to follow this tutorial https://truffleframework.com/tutorials/building-dapps-for-quorum-private-enterprise-blockchains. I configured 2_deploy_simplestorage.js at is mentionned and the command deployer.deploy(SimpleStorage, 42, {privateFor: ['ROAZBWtSacxXQrOe3FGAqJDyJjFePR5ce4TSIzmJ0Bc...
MS B
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2

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383

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Cross-ledger communication between Hyperledger Fabric and Hyperledger Indy

Is it possible to have a cross-ledger identity management between hyperledger fabric and indy? Is it possible to communicate between Hyperledger Fabric and Hyperledger Indy? Can I read the data from Fabric and store it in Indy and vice-versa? My idea is to use Indy to authenticate identities and us...
Abhinay B
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Is the Proof of Elapsed Time consensus mechanism in blockchains Byzantine Fault Tolerant?

I was looking at consensus mechanisms other than the common PoW and PoS, and found a scheme known as proof of elapsed time. I am struggling to find any research or proofs to show that this is in fact a Byzantine Fault Tolerant algorithm.
BOB
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How to convert uint to string in solidity?

In Solidity, is there a way I can convert my int to string ? Example: pragma solidity ^0.4.4; contract someContract { uint i; function test() pure returns (string) { return 'Here and Now is Happiness!'; } function love() pure returns(string) { i = i +1; return 'I love ' + functionname(i) + ' person...
Bob Zheng
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2

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Single organization Hyperledger fabric n/w

What are the implications, If I use hyperledger fabric's blockchain for a distributed ledger for myself. I mean I 'm not having anything to do with any other Org. So this becomes my tamper proof database for certain applications or records. Will it have trust issues? I need the consensus to be amon...
Ashish Mishra
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Sawtooth Transaction error: “Tried to set unauthorized address”

I am trying to write my custom Transaction processor. I am writing for simple Account class class Account: def __init__(self, name, ac_number, balance): self.name = name self.ac_number = ac_number self.balance = balance My TP is working fine for a single account. Now I want to improve it for mult...
Harun-Ur-Rashid
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put and get json in ledger using go

I am quite new to Go programming. I am trying to insert a json into blockchain ledger and read it back using golang. My json looks like below: var jsonBytes = []byte(`[{'FLD1':10,'Fld2':'ABC'}, {'FLD1':100,'Fld2':'0.26'}]`) Ultimately, this json will be used as a look up table in my blockchain code....
user1456110
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Fatal error: runtime:out of memory during install of geth

# make geth build/env.sh go run build/ci.go install ./cmd/geth >>>/usr/lib/golang/bin/go install -ldflags -X main.gitCommit= -v github.com/ethereum/go-ethereum/dashboard # github.com/ethereum/go-ethereum/dashboard fatal error: runtime: out of memory runtime stack: util.go:45: exit status 2 exit s...
Jerry Hu
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149

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Cryptic Babel error in React web app when using Stellar SDK

Im developing a web app using React JS(Using Create React App) which will run on Stellar and Im using the official JS Stellar SDK. However, after integrating the Stellar SDK, I get a Babel error due to the Stellar SDK. Has anyone faced this issue before? The error is as follows : ./node_modules/js-x...
SeaWarrior404
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In a PoW(Proof-of-Work) blockchain of length N, how difficult is to modify the (N-2)th block?

So I was going through a few resources(link) on how to implement a PoW Blockchain, and reaod this: If the data in block 44 is changed from “DESERT” to “STREET”, all hashes of the consecutive blocks must be changed. This is because the hash of the block depends on the value of the previousHas...
Ayush Gupta
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Hyperledger installation issue with docker

This is a first time i am testing hyperkedger bloackchain framework but I am facing some issues. I am trying to install hyperledger on ubuntu image, everything were fine as per the instructions mentioned in this site https://hyperledger.github.io/composer/installing/development-tools.html . But afte...
wolvorinePk
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Ethereum Error: Transaction was not mined within 50 blocks

info: Error: Transaction was not mined within 50 blocks, please make sure your transaction was properly send. Be aware that it might still be mined! at /opt/bkzcoin_project/bkzcoin-backend/node_modules/web3-core-method/src/index.js:375:45 at tryCatcher (/opt/bkzcoin_project/bkzcoin-backend/node_mod...
Elisabeth Shevtsova
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2

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368

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Querying the ledger in Hyper Ledger Fabric Network

I have refereed below link for Querying into the ledger in Hyper-ledger Fabric Network : http://hyperledger-fabric.readthedocs.io/en/release/write_first_app.html In above link, they have given git-hub link in which I have done all the steps like, - start the network - run the node scripts for queryi...
Riya Soni
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2

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788

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How to generate Ethereum wallets(private/public keys) for users using PHP/JS?

I need to generate Ethereum wallets for each user of my site. I need to get private and public keys. How to do it using PHP or Javascript? For Ethereum I found web3.js library which I can use for getting access to an ethereum nodes, but I see examples only for checking balances or sending transactio...
Valentine Murnik
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Can Merkle tree tell if more than one copy of the object exist in it?

With Merkle root hash, and Merkle path, one can verify if a given object (i.e a transaction) exist in a Merkle tree. But is it possible to tell there is no other duplication of the object in the tree. For example, if I have the Merkle root of a list of transactions and the Merkle path of one transac...
Leo Zhang
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Sett up multuihost Hyperledger-Fabric environment with Hyperledger-Celllo

My current setup is I already have VMs in azure cloud running with ubuntu on it I need to setup multihost Hyperledger fabric network on that I am trying that with cello project I have created runhosts.tpl in cello/src/agent/ansible/run/ with details of public IP and private IP when I try to run ansi...
Darshu Bc
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Is it possible to build network map cluster on Corda?

Is it possible to build a network map cluster to allow high availability and to prevent single point of failure from using a single node?
BenNad
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Hyperledger Composer Playground Business Logic relationship

I'm tasked with learning about HyperLedger Fabric, and I'm supposed to build a business network that has many companies (participants), each company has many Outboxes (also Participants?). Each Outbox can write Messages(Assets) to the Blockchain. However, only the company to which the Outbox belongs...
wurstbrot
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3

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4.8k

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How to label x-Axis in Chart.js by days?

I'm currently trying to fetch data from blockchain.info and to display it on a Chart.js in a simple JavaScript file. It works just fine if my xAxes type is 'linear', but in that case the labels on the x-Axis are displayed with the numeric unix timestamp. xAxes: [{ type: 'linear', time: { unit: 'day...
Pascal S
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349

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Cannot install EncCC chaincode

I am trying to test Fabric chaincode encryption capabilities introduced in version 1.1 with EncCC chaincode. The tutorial on github starts from the moment when it is assumed that chaincode is already installed. I manage to install the chaincode by importing bcssp and ext/entities but instantiation f...
99hardforks
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What parts of Hyperledger Fabric effect the scalability?

So from my understanding, kafka based ordering is what would be used in a production environment. Within a Kafka based ordering environment we have: Zookeeper nodes Kafka nodes Orderer Nodes Peer Nodes Within this environment which of these would effect scalability most or at all? I am currently w...
zonked
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Using blockchain info from wallet in code

I have a crypto wallet that is synced with the network that has the current block height the amount of coins difficulty, status(locked, unlocked) etc information I need. I would like to program a batch file that looks at the current block height and executes commands to the wallet if that height mat...
Tanner Russell
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How does it the geth ethereum platform to automatically connect to the nodes that are in the main network of Ethereum?

I have tried to make connection between several nodes in my private network, but I do it with a direction enode, but Ethereum network does it without knowing my address enode, I want to know what kind of p2p communication protocols used so that all nodes are communicate with each other, and if that...
Astrid Villanueva
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Error while Fetching Hash value for a block chain

I am working on a sample blockchain implementation with dummy data. I have One method is createGenesisBlock() for creating first block and other method is Makeblock() for blockchain. The code is written in python 3.6 I am facing issue with Makeblock when retrieving the Hash Value created in Genesis...
Dhiraj Kumar
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51

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UnsupportedOperation: not writabl, in python while counting coins in chainsaw

What I'm trying to do is to print ot the total number of coins in blockchain. I'm working with the examples from the Chainscan manual Here is my code so far: from chainscan import iter_blocks total_btc = 0 for block in iter_blocks(show_progressbar = True): coinbase_tx = next(iter(block.txs)) # th...
Jürgen K.
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260

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hyperledger fabric - stuck at creating cli

I was building the network at fabric level. Following this tutorial http://hyperledger-fabric.readthedocs.io/en/latest/build_network.html I have made changes in the following files and added 2 more peers in organisation1 only. configtx.yaml crypto-config.yaml docker-compose-cli.yaml docker-compose-c...
PKB
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230

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What contract is used in Istanbul consensus mechanism in JP Morgan Quorum?

In '7nodes' installation example from JPMorgan Quorum github is used such a genesis file ('istanbul-genesus.json'): { 'alloc': { '0x0000000000000000000000000000000000000020': { 'code': '0x606060405236156100c45760e060020a60003504631290948581146100c9578063284d163c146100f957806342169e481461013057806348...
Nick Kernel
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182

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Blockchain wallet send api not working

I am trying to send the btc by using blockchain wallet. Check Balance, create address all are working fine. But when i am trying to send the btc to address. It gives me the error below:- {'error':'Unexpected error, please try again'} This is what i am calling for sending btc:- http://localhost:3000/...
Deepak Rana
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1

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586

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Truffle contract works with Ganache but not on Testnet

I was able to create and deploy a contract locally to Ganache using Truffle. I could set and get a value successfully as well. I deployed this contract to both Rinkeby and Ropsten and was able to call the get function, but the set function failed with the error: Error: Invalid JSON RPC response: ''...
Seth Sacher
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1

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571

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How to create participant , there identities via rest api that generated by composer rest server without importing cards via /importwallets?

I have created bna and deployed in composer rest server by enabling passport and multi-user, How to create participant, their identities via rest API that generated by composer rest server without importing cards via import wallets? and there is no proper documentation for this.
user3739891
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400

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Ethereum private blockchain empty blocks mining

I have set up a private block chain with 2 nodes 1 being a miner node . However we are seeing lots of empty blocks being mined . i tried the solution suggested at this link https://ethereum.stackexchange.com/questions/3151/how-to-make-miner-to-mine-only-when-there-are-pending-transactions . But stil...
redeemed
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How to create raw transaction using web3swift?

I'm working on a project related to blockchain and need to figure out how raw transaction can be possible. I got no reference for this as of now. I have tried matterinc/web3swift but unable to get exact thing.
Abhishek Thapliyal
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96

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blockchain.info API key Error “ Request already present”

I am trying to make API key in my localhost to test API to connect to Wallet. by using this url: https://api.blockchain.info/customer/signup when i entered url (http://localhost) i got this error: Error ' Request already present' How can i get API key to use it in my localhost? also,when i tried to...
Mohamed Amin
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50

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Are DAG-based crypto currencies as secure as proof-of-work based blockchains?

A key feature of blockchain based cryptocurrencies is that they provide inherently secure systems that don't rely on trusted third parties. The newer DAG-based cryptos like Byteball are being touted as superior to blockchains because they have faster transaction times and eliminate the need for mine...
Mike Collins
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62

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Unable to add password field in balance transfer example in hyperledger fabric

Actually i want to add password field in balance transfer example but i am getting unhandled rejection error in json. please anyone resolve the issue. curl -s -X POST \ http://localhost:4000/users \ -H 'content-type: application/x-www-form-urlencoded' \ -d 'username=Jim&orgName=org1&password=S...
Subramanyam
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Gas required exceeds limit: 3000000.

pragma solidity ^0.4.16; contract createNewToken { uint256 total_ether_to_send; address private owner; //constructor function createNewToken() public{ owner = msg.sender; } // client request for tokens by sending ether. function requestForToken() public payable{ address sender = msg.sender; uint val...
Harsh
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209

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Unable to Query Chain Code

I have a simple Invoke function that calls 2 methods depending upon arguments as shown below: func (t *SimpleChaincode) Invoke(stub shim.ChaincodeStubInterface) pb.Response { fmt.Println('chaincode_custom Invoke') function, args := stub.GetFunctionAndParameters() if function == 'addProduct'{ retur...
Atif
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57

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How to get the total amount sent to an Etherum address

I'm a noob at Ethereum and need to make statistics from blockchain data. I have a full node up and running with RPC ready, but can't find a clue in the doc on how to query : Total number of transactions in/out for a contract/address Total number of ether sent/received for a contract/address The onl...
simon
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167

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Hyperledger fabric - Migrate a channel from one network to another network.

Suppose I 'm running a two fabric networks for my Org, which is hosting few different channels. Network A is having channel 1, 2 and 3. Network B is having channel 4, 5 and 6. Now say channel 3 has many transactions and it's growing at an exponential rate so I decided to separate that channel on a...
Ashish Mishra
1

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1

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94

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Why do you need an browser extension like MetaMask to make transactions on Ethereum?

What is stopping web apps from accessing and making transactions directly on the blockchain?
Ali Abdelhadi

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