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Java Validate Ethereum Address

How To Send Ethereum Transactions With Java

How To Send Ethereum Transactions With Java

How to Send Ethereum Transactions With Java How to Send Ethereum Transactions With Java If you're Java developer dipping into the Ethereum blockchain, here's what you need to know about the ins and outs of sending transactions. Aug. 11, 17 Java Zone Build vs Buy a Data Quality Solution: Which is Best for You? Gain insights on a hybrid approach. Download white paper now! After Ive expressed my concerns about the blockchain technology , lets get a bit more practical with the blockchain. In particular, with Ethereum. I needed to send a transaction with Java, so I looked at EthereumJ . You have three options: Full node you enable syncing, which means the whole blockchain gets downloaded. It takes a lot of time, so I abandoned that approach Light node you disable syncing, so you just become part of the network, but dont fetch any parts of the chain. Not entirely sure, but I think this corresponds to the light mode of geth (the Ethereum CLI). You are able to send messages (e.g. transaction messages) to other peers to process and store on the blockchain, but you yourself do not have the blockchain. Offline (no node) just create and sign the transaction, compute its raw representation (in the Ethereum RLP format) and push it to the blockchain via a centralized API, e.g. the etherscan.io API . Etherscan is itself a node on the network and it can perform all of the operations (so it serves as a proxy) Before going further, maybe its worth pointing out a few general properties of the blockchain (the Ethereum one and popular cryptocurrencies at least) it is a distributed database, relying on a peer-to-peer (overlay) network, formed by whoever has a client software running (wallet or otherwise). Transactions are in the form of I (private key owner) want to send this amount to that Continue reading >>

A Hacker Stole $31m Of Etherhow It Happened, And What It Means Forethereum

A Hacker Stole $31m Of Etherhow It Happened, And What It Means Forethereum

A hacker stole $31M of Ether how it happened, and what it means forEthereum Yesterday, a hacker pulled off the second biggest heist in the history of digital currencies. Around 12:00 PST, an unknown attacker exploited a critical flaw in the Parity multi-signature wallet on the Ethereum network, draining three massive wallets of over $31,000,000 worth of Ether in a matter of minutes. Given a couple more hours, the hacker couldve made off with over $180,000,000 from vulnerable wallets. Having sounded the alarm bells, a group of benevolent white-hat hackers from the Ethereum community rapidly organized. They analyzed the attack and realized that there was no way to reverse the thefts, yet many more wallets were vulnerable. Time was of the essence, so they saw only one available option: hack the remaining wallets before the attacker did. By exploiting the same vulnerability, the white-hats hacked all of the remaining at-risk wallets and drained their accounts, effectively preventing the attacker from reaching any of the remaining $150,000,000. To prevent the hacker from robbing any more banks, the white-hats wrote software to rob all of the remaining banks in the world. Once the money was safely stolen, they began the process of returning the funds to their respective account holders. The people who had their money saved by this heroic feat are now in the process of retrieving their funds. Its an extraordinary story, and it has significant implications for the world of cryptocurrencies. Its important to understand that this exploit was not a vulnerability in Ethereum or in Parity itself. Rather, it was a vulnerability in the default smart contract code that the Parity client gives the user for deploying multi-signature wallets. This is all pretty complicated, so to make th Continue reading >>

Web3j Milestone V1.0 Release

Web3j Milestone V1.0 Release

Today web3j has hit the milestone 1.0 release, providing a number of key pieces of functionality for integrating Java applications with Ethereum: Complete implementation of Ethereum's JSON-RPC client API Auto-generation of Java smart contract wrappers to create, deploy, transact with and call smart contracts from native Java code Support for Parity's Personal, and Geth's Personal client APIs Support for Infura, so you don't have to run an Ethereum client yourself Comprehensive documentation and integration tests web3j started off as a simple Java library for Java applications to communicate with Ethereum clients over JSON-RPC. However, it rapidly morphed into a fully featured library for working with Ethereum clients. The integration with JSON-RPC was only one of the challenges faced by applications wishing to work with Ethereum. I found that there were a number of additional obstacles that developers needed to overcome to effectively work with the client JSON-RPC API. The 1.0 release addresses these: Conversion to and from Solidity's primitive types which differ from those used in Java - for instance, its native numeric type is 256 bits Encoding/de-decoding of these Ethereum types into Ethereum's Application Binary Interface (ABI), and Recursive Length Prefix (RLP) formats for transmission over JSON-RPC Secure transaction signing using Elliptic Curve Digital Signature Algorithms Secure creation of and management of Ethereum wallet files, and associated public/private keys Identification of unique transaction identifiers (nonces) prior to sending new transactions No direct integration existing for working with smart contracts written in Solidity from Java code The lack of a single source of comprehensive documentation for working with the platform for Java developers I Continue reading >>

Connecting To The Network

Connecting To The Network

Distribution of client implementations on the current live network - Realtime stats on EtherChain. Public, private, and consortium blockchains Most Ethereum projects today rely on Ethereum as a public blockchain, which grants access to a larger audience of users, network nodes, currency, and markets. However, there are often reasons to prefer a private blockchain or consortium blockchain (among a group of trusted participants). For example, a number of companies in verticals, like banking, are looking to Ethereum as a platform for their own private blockchains. Below is an excerpt from the blog post On Public and Private Blockchains that explains the difference between the three types of blockchains based on permissioning: Public blockchains: a public blockchain is a blockchain that anyone in the world can read, anyone in the world can send transactions to and expect to see them included if they are valid, and anyone in the world can participate in the consensus process the process for determining what blocks get added to the chain and what the current state is. As a substitute for centralized or quasi-centralized trust, public blockchains are secured by cryptoeconomics the combination of economic incentives and cryptographic verification using mechanisms such as proof of work or proof of stake, following a general principle that the degree to which someone can have an influence in the consensus process is proportional to the quantity of economic resources that they can bring to bear. These blockchains are generally considered to be fully decentralized. Consortium blockchains: a consortium blockchain is a blockchain where the consensus process is controlled by a pre-selected set of nodes; for example, one might imagine a consortium of 15 financial institutions, each of Continue reading >>

Listing Accounts And Checking Balances

Listing Accounts And Checking Balances

From the command line, call the CLI with: $ geth account listAccount #0: {d1ade25ccd3d550a7eb532ac759cac7be09c2719}Account #1: {da65665fc30803cb1fb7e6d86691e20b1826dee0}Account #2: {e470b1a7d2c9c5c6f03bbaa8fa20db6d404a0c32}Account #3: {f4dd5c3794f1fd0cdc0327a83aa472609c806e99} to list your accounts in order of creation. Note:This order can change if you copy keyfiles from other nodes, so make sure you either do not rely on indexes or make sure if you copy keys you check and update your account indexes in your scripts. # Request$ curl -X POST --data '{"jsonrpc":"2.0","method":"eth_accounts","params":[],"id":1} Result{ "id":1, "jsonrpc": "2.0", "result": ["0x407d73d8a49eeb85d32cf465507dd71d507100c1"]} If you want to use an account non-interactively, you need to unlock it. You can do this on the command line with the --unlock option which takes a whitespace separated list of accounts (in hex or index) as argument so you can unlock the accounts programmatically for one session. This is useful if you want to use your account from Dapps via RPC. --unlock will unlock the first account. This is useful when you created your account programmatically, you do not need to know the actual account to unlock it. geth --password <(echo this is not secret!) account new geth --password <(echo this is not secret!) --unlock primary --rpccorsdomain localhost --verbosity 6 2>> geth.log Instead of the account address, you can use integer indexes which refers to the address position in the account listing (and corresponds to order of creation) The command line allows you to unlock multiple accounts. In this case the argument to unlock is a whitespace delimited list of accounts addresses or indexes. geth --unlock "0x407d73d8a49eeb85d32cf465507dd71d507100c1 0 5 e470b1a7d2c9c5c6f03bbaa8fa20db6d40 Continue reading >>

Interfacing With Ethereum Smart Contracts Injava

Interfacing With Ethereum Smart Contracts Injava

Interfacing with Ethereum Smart Contracts inJava Since quite a lot of business applications are written in Java, or make use of the JVM for that matter, I believe a primer on how to interface with an Ethereum Smart Contract in Java will prove helpful to the reader. This post requires knowledge of what a Smart Contract is and how to deploy one. To learn why we will probably use a library for interfacing with the Smart Contract a basic understanding of the usage of JSON-RPC in Ethereum is necessary. Lets unveil the supposed magic behind what almost all Ethereum libraries do to interact with the blockchain. Suppose we need to know the gasLimit (maximum amount of computational effort the transactions in a block are allowed to have) of the latest block. Using curl and piping its result to a JSON parser such as jq would, considering we run an Ethereum node on localhost port 8545, look as follows curl --silent -X POST -H "Content-Type: application/json"\ --data '{"jsonrpc":"2.0","method":"eth_getBlockByNumber","params":["latest", true],"id":1}' localhost:8545 | jq .result.gasLimit The above will yield 0x4c4b3c, which is hex-encoded . Since we probably want to read it as a decimal we can add another pipe and the final command becomes curl --silent -X POST -H "Content-Type: application/json" --data '{"jsonrpc":"2.0","method":"eth_getBlockByNumber","params":["latest", true],"id":1}' localhost:8545\ Leading to the readable result of 4999996. These steps involved are a good showcase on why to introduce an abstraction. Almost all libraries will provide convenient interfaces for these RPC calls. Using the library web3j the command above will translate to web3j.ethGetBlockByNumber(DefaultBlockParameter.valueOf("latest"), Still a lot of steps, and from a software-engineering perspecti Continue reading >>

Create A Democracy Contract In Ethereum

Create A Democracy Contract In Ethereum

"On the Blockchain, no one knows you're a fridge" So far, all contracts we listed were owned and executed by other accounts probably held by humans. But there is no discrimination against robots or humans in the Ethereum ecosystem and contracts can create arbitrary actions like any other account would. Contracts can own tokens, participate in crowdsales, and even be voting members of other contracts. In this section we are going to build a decentralized and democratic organization that exists solely on the blockchain, but that can do anything that a simple account would be able to. The organization has a central manager that decides who are the members and the voting rules, but as we'll see, this can also be changed. The way this particular democracy works is that it has an Owner which works like an administrator, CEO or a President. The Owner can add (or remove) voting members to the organization. Any member can make a proposal, which is in the form of an ethereum transaction to either send ether or execute some contract, and other members can vote in support or against the proposal. Once a predetermined amount of time and a certain number of members has voted, the proposal can be executed: the contract counts the votes and if there are enough votes it will execute the given transaction. pragma solidity ^0.4.16;contract owned { address public owner; function owned() public { owner = msg.sender; } modifier onlyOwner { require(msg.sender == owner); _; } function transferOwnership(address newOwner) onlyOwner public { owner = newOwner; }}contract tokenRecipient { event receivedEther(address sender, uint amount); event receivedTokens(address _from, uint256 _value, address _token, bytes _extraData); function receiveApproval(address _from, uint256 _value, address _token, byt Continue reading >>

Transactions Web3j 3.3.1 Documentation

Transactions Web3j 3.3.1 Documentation

Mining it yourself in a private environment, or the public test environment (testnet) is verystraight forwards. However, in the main live environment (mainnet) it requires significantdedicated GPU time which is not likely to be feasible unless you already have a gaming PC withmultiple dedicated GPUs. If you wish to use a private environment, there is some guidance on the Homestead documentation . To purchase Ether you will need to go via an exchange. As different regions have differentexchanges, you will need to research the best location for this yourself. The Homestead documentation contains a number of exchanges which is a good place to start. There are a number of dedicated test networks in Ethereum, which are supported by various clients. For development, its recommended you use the Rinkeby or Kovan test networks. This is because theyuse a Proof of Authority (PoA) consensus mechanism, ensuring transactions and blocks are created ina consistent and timely manner. The Ropsten testnet, although closest to the Mainnet as it usesProof of Work (PoW) consensus, has been subject to attacks in the past and tends to be moreproblematic for developers. You can request Ether for the Rinkeby testnet via the Rinkeby Crypto Faucet, available at . Details of how to request Ether for the Kovan testnet are available here . If you need some Ether on the Ropsten testnet to get started, please post a message with yourwallet address to the web3j Gitter channel and you will besent some. In the Ethereum test environment (testnet), the mining difficulty is set lower then the mainenvironment (mainnet). This means that you can mine new Ether with a regular CPU, such as yourlaptop. What youll need to do is run an Ethereum client such as Geth or Parity to start buildingup reserves. Further ins Continue reading >>

How To Send Ethereum Transactions With Java

How To Send Ethereum Transactions With Java

After Ive expressed my concerns about the blockchain technology , lets get a bit more practical with the blockchain. In particular, with Ethereum. I needed to send a transaction with Java, so I looked at EthereumJ . You have three options: Full node you enable syncing, which means the whole blockchain gets downloaded. It takes a lot of time, so I abandoned that approach Light node you disable syncing, so you just become part of the network, but dont fetch any parts of the chain. Not entirely sure, but I think this corresponds to the light mode of geth (the ethereum CLI). You are able to send messages (e.g. transaction messages) to other peers to process and store on the blockchain, but you yourself do not have the blockchain. Offline (no node) just create and sign the transaction, compute its raw representation (in the ethereum RLP format) and push it to the blockchain via a centralized API, e.g. the etherscan.io API . Etherscan is itself a node on the network and it can perform all of the operations (so it serves as a proxy) Before going further, maybe its worth pointing out a few general properties of the blockchain (the ethereum one and popular cryptocurrencies at least) it is a distributed database, relying on a peer-to-peer (overlay) network, formed by whoever has a client software running (wallet or otherwise). Transactions are in the form of I (private key owner) want to send this amount to that address. Transactions can have additional data stored inside them, e.g. representing what they are about. Transactions then get verified by peers (currently using a Proof-of-work based consensus) and get stored on the blockchain, which means every connected peer gets the newly created blocks (each block consisting of multiple transactions). Thats the blockchain in short, Continue reading >>

Integrating The Ethereum Blockchain Into Java Apps

Integrating The Ethereum Blockchain Into Java Apps

Integrating the Ethereum Blockchain into Java Apps How to access a distributed ledger technology blockchain from a Java application using web3j. The Ethereum blockchain is a decentralized platform that is the backbone of a secure, decentralized internet and is driven by the eponymous cryptocurrency Ether. Conor Svensson authored web3j, a lightweight Java library for building Java applications on the Ethereum blockchain. In a first article , which appeared in the Java Magazine, Conor Svensson gives the background of the Ethereum blockchain technology and explains how to create a blockchain that is connected to a Java application. Web3j, a wrapper of client remote procedure calls using JSON, manages the transaction interactions with Ethereum clients. In a second article , he details how to use web3j to query the Ethereum blockchain via its reactive-functional API. He explains how to use RxJavas Observables to add reactive functionality to theblockchain. An Ethereum client like Geth or Parity is the first step to getting you started. Clients will synchronize the Ethereum blockchain with one another and provide a gateway to interact with the blockchain. Ethereum takes care of Ether cryptocurrency payment transactions via the network. With just a few lines of code, you can hook up to the Ethereum blockchain and be notified of new blocks being added to the blockchain and start pulling information out of the blockchain in real time. For code and step by step examples, read the full article here for more information, please visit: web3j project and Conor's blog Continue reading >>

Ethereum In Practice - Quick Start Guide

Ethereum In Practice - Quick Start Guide

Ive found Ethereum documentation to be very thorough. And yet,Ive found it hard to understand how to approach Ethereum in practice - connect to the network, developand debug of a contract, deploy it and actually use it. This is what this post / guide / tutorial, and few coming posts, are about.Straight and to the point. This post certainly doesnt cover the theory which is already well explained in the official documentation, butrather focuses on how to get one up and running in, really, few minutes; because it is really that simple when you know how. And also when you know some theory as well. So, if you didnt read the official documentation, please, do so. Thispost assumes that at the very least one knows what Ethereum is and how it works and what an account, an EOA, a contract, gas and transactions are ,and finally would like to put it all to practice. There is a bare minimum of basic theory below otherwise. Here, in this post, following subject are covered: Run a private network, create a contract and deploy it to Homestad Ethereum network is decentralized. It means that there is no central server and what is called ethereumclient (like eth or geth for example) is really a part of the network when it is online. The network is allclients altogether. You know BitTorrent, right? So this is kind of the same, but better. So, step #1 - install the client. Again, there is no single client, there are multiple to chose from. Ethereum isdescribed in a specification, and multiple clients exist all implementing it. But really, as of the time of thiswriting, the most popular is geth, which is my choice as well, and which is the one used throughout this post in theexamples. Install instructions depend on the OS, so Im just pointing to geth GitHub repository . If you see the geth Continue reading >>

Coinbase Digital Currency Api

Coinbase Digital Currency Api

Coinbase provides a simple and powerful REST API to integrate bitcoin, bitcoin cash, litecoin and ethereum payments into your business or application. This API reference provides information on available endpoints and how to interact with it. To read more about the API, visit our API documentation . Note: If youre still using legacy Coinbase API (v1), you should access relevant API reference , Wallet API and Merchant API documentation. This API supports two modes of authentication: API key - Useful to access your own account OAuth2 (Coinbase Connect) - Used to build applications for Coinbase users curl \ -H "Authorization: Bearer abd90df5f27a7b170cd775abf89d632b350b7c1c9d53e08b340cd9832ce52c2c" OAuth2 is recommended when youre creating an application for others on top of Coinbase platform. This authentication provides a secure and easy to use authentication flow for users. OAuth2 requests must be authenticated with a valid access token passed as bearer token. To use the bearer token, construct a normal HTTPS request and include an Authorization header with the value of Bearer. Signing is not required. API key is recommend if you only need to access your own account. All API key requests must be signed and contain the following headers: CB-ACCESS-SIGN The user generated message signature (see below) CB-ACCESS-TIMESTAMP A timestamp for your request All request bodies should have content type application/json and be valid JSON. The CB-ACCESS-SIGN header is generated by creating a sha256 HMAC using the secret key on the prehash string timestamp + method + requestPath + body (where + represents string concatenation). The timestamp value is the same as the CB-ACCESS-TIMESTAMP header. The body is the request body string or omitted if there is no request body (typically for GE Continue reading >>

Ether - How Can I Check If An Ethereum Address Is Valid? - Ethereum Stack Exchange

Ether - How Can I Check If An Ethereum Address Is Valid? - Ethereum Stack Exchange

How can I check if an Ethereum address is valid? I've read many times that you should never input an address by hand unless you want to accidentally send Ether into no-mans-land. I'd like to know what those checksums might be. Is there a way to tell a typo is occurred? how, and what are the formatting rules to it? Im asking so I can potentially create a wrapper function that checks for these things before submitting to the network. Updated May 2016: EIP 55 added a "capitals-based checksum" and has been implemented by Geth.Here's Javascript code from Geth: /** * Checks if the given string is an address * * @method isAddress * @param {String} address the given HEX adress * @return {Boolean}*/var isAddress = function (address) { if (!/^(0x)?[0-9a-f]{40}$/i.test(address)) { // check if it has the basic requirements of an address return false; } else if (/^(0x)?[0-9a-f]{40}$/.test(address) || /^(0x)?[0-9A-F]{40}$/.test(address)) { // If it's all small caps or all all caps, return true return true; } else { // Otherwise check each case return isChecksumAddress(address); }};/** * Checks if the given string is a checksummed address * * @method isChecksumAddress * @param {String} address the given HEX adress * @return {Boolean}*/var isChecksumAddress = function (address) { // Check each case address = address.replace('0x',''); var addressHash = sha3(address.toLowerCase()); for (var i = 0; i < 40; i++ ) { // the nth letter should be uppercase if the nth digit of casemap is 1 if ((parseInt(addressHash[i], 16) > 7 && address[i].toUpperCase() !== address[i]) || (parseInt(addressHash[i], 16) <= 7 && address[i].toLowerCase() !== address[i])) { return false; } } return true;}; ICAP has a checksum which can be verified. You can review Geth's icap.go and here's a snippet from it: // val Continue reading >>

Innovating With Bolos : Building An Ethereum Hardware Wallet

Innovating With Bolos : Building An Ethereum Hardware Wallet

Innovating with BOLOS : building an Ethereum Hardware Wallet We might have started the wrong app.Oopsie. In our previous article we introduced BOLOS: a platform to innovate around the edges of Personal Security Devices, making sure that your private data stays protected when using embedded third party applications. Well have a look today at an interesting example from the point of view of an Hardware Wallet designer: how to enhance the security of a significantly different blockchain, Ethereum. This is of course in no way an investment advice just a nice use case which is complex enough to make it hard to implement on a legacy Hardware Wallet, yet simple enough to use it as a BOLOS API training. Also were still large Ethereum newbies, so expect gross oversimplifications and a few mistakes. The cryptographic and protocol parts should make sense though. An Ethereum primer for Bitcoin Hardware Wallet developers On the easy side, Ethereum user accounts (Externally Owned Accounts) rely on transactions that are more simple than Bitcoin transactions (as the system maintains a state and balance, no inputs are involved) and use the same secp256k1 ECDSA signature scheme than Bitcoin. However the hash algorithm and transaction encoding used are slightly different. Ethereum also handles contract accounts which are managed directly by code and therefore out of scope of Hardware Wallet security as the state of the network guarantees that their execution is consistent. The hash algorithm used is the pre-release version of SHA-3, Keccak-256 this can be a bit confusing for newcomers as SHA-3 is released now, and it is quite important to use the right version of the algorithm as it is also used to generate Ethereum addresses, which have no checksum. It is fairly easy to add if your comp Continue reading >>

Ether Transfer From One Account To Another Account Using Web3j And Java

Ether Transfer From One Account To Another Account Using Web3j And Java

Ether transfer from one account to another account using Web3j and Java Posted by Sudhakar Pandey | Last Updated: 28-Sep-17 from one account to another account. We need to do following steps for ether transfer- You need to add web3j dependency in maven as Create Web3j object to connect ethereum server. Web3j web3j = Web3j.build(new HttpService("Ethereum server ip with port")); After that you need to calculate transaction fee which is essential for doing transaction. Transaction fee will be equal to gas * gas price, i.e. minimum gas required for transation is 21000. After that we need to create credenials object as Credentials credentials = WalletUtils.loadCredentials( "Password of sender account", "Ethereum server blockchain keystore path" + "/" + "Sender account wallet file name"); Then we need to validate amount which we want to transfer in another amount either this amount is exists in sender amount or not. After that used below function for transfer public Map transferEtherAccountToAccount(BigDecimal balance) throws IOException { Map result = new HashMap<>(); try { Web3j web3j = Web3j.build(new HttpService(envConfiguration.getTestnetServerIp())); LOGGER.info("--------------Enter into transferEtherAccountToAccount function"); // Find the wallet from database which is used as sender address UserWallet wallet = userWalletRepository.findByAddress(address); BigInteger amount = web3j.ethGetBalance(wallet.getAddress(), DefaultBlockParameterName.fromString("latest")).send() .getBalance(); LOGGER.info("Creating Parity..."); LOGGER.info("Getting wallet ..." + wallet.getAddress() + " and balance is " + web3j.ethGetBalance(wallet.getAddress(), DefaultBlockParameterName.fromString("latest")).send() .getBalance()); // Minimum gas is 21000 used for transaction BigInteger gas = Bi Continue reading >>

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