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Storage - How Can I Store Data In Ethereum Blockchain - Ethereum Stack Exchange

Storage - How Can I Store Data In Ethereum Blockchain - Ethereum Stack Exchange

How can I store data in ethereum blockchain I want to store pdf hash in blockchainI already read this post What are some proposed ways of storing data in Ethereum? But I'm beginner in this domain and I don't understand... Is it possible to store data (hash in my case) in Ethereum? How many cost to store data in Ethereum? And how can I do this with python or an other language? In a special place on the blockchain reserved for contract data In a special place on the blockchain reserved for transaction input data To store your data in a special place 1 you'll need to create a contract and deploy it on the blockchain. To store your data in a special place 2 you'll need to send someone a transaction and include your data in it. Before you you can interact with the blockchain you will need to get access to the web3 object. There are multiple ways of doing so. I'd suggest you installing MetaMask plugin for Chrome browser. After you install it, you will have access to web3 object. The ways of interacting with web3 object can be found here (web3 api documentation) Now that you've installed MetaMask plugin. Choose Morden testnet in the configs. Now you can use solidity browser compiler . Try to compile and deploy a simple contract there: You will need some ether in your account(MetaMask provided account) to deploy contracts. Go to and get 5 testnet ether for free. And after I install web3, could I store data in a special place 1? wxcvbn Aug 9 '16 at 12:15 @wxcvbn, I updated my response, check it out, feel free to ask Eugene Epifanov Aug 9 '16 at 12:26 Thank a lot for your answer! Can I insert several hash in one contract? Or is it possible to open an existing contract and add a hash? I need some ether for each contract created or for each data insert in contract? wxcvbn Aug 9 '1 Continue reading >>

What Is Ethereum? - Coindesk Guides

What Is Ethereum? - Coindesk Guides

Before you can understand ethereum, it helps to first understand the internet. Today, our personal data, passwords and financial information are all largely stored on other people's computers in clouds and servers owned by companies like Amazon, Facebook or Google. Even this CoinDesk article is stored on a server controlled by a company that charges to hold this data should it be called upon. This setup has a number of conveniences, as these companies deploy teams of specialists to help store and secure this data, and remove the costs that come with hosting and uptime. But with this convenience, there is also vulnerability. As we've learned, a hacker or a government can gain unwelcome access to your files without your knowledge, by influencing or attacking a third-party service meaning they can steal, leak or change important information. Brian Behlendorf, creator of the Apache Web Server, has gone so far as to label this centralizeddesign the "original sin" of the Internet. Some like Behlendorf argue the Internet was always meant to be decentralized, and a splintered movement has sprung up around using newtools, including blockchain technology, to help achieve this goal. Ethereum is one of the newest technologies to join this movement. While bitcoin aims to disrupt PayPal and online banking, ethereum has the goal of using a blockchain to replace internet third parties those that store data, transfer mortgages and keep track of complex financial instruments. In short, ethereum wants to be a 'World Computer' that would decentralize and some would argue, democratize the existing client-server model. With ethereum, servers and clouds are replaced by thousands of so-called "nodes" run by volunteers from across the globe (thus forming a "world computer"). The vision is that Continue reading >>

My Personal Experience: How Does The Ethereum Blockchain Work?

My Personal Experience: How Does The Ethereum Blockchain Work?

My Personal Experience: How Does The Ethereum Blockchain Work? The Ethereums blockchain is a complex topic that requires programming knowledge to fully understand it. Because the majority of us dont have that level of knowledge, Ill explain it in basic terms without going too deep into the details, from my experience as an Ethereum developer with more than 4 projects completed and 6+ months working on Smart Contracts: First Ill explain you the purpose of the Ethereums blockchain to understand why it exists and what problem it solves. Then well go to into specific use cases of whats possible. Traditionally, when 2 people want to buy something or perform a transaction of some kind in the online world, they have to trust an intermediary that will move the money from an account to the other. So for example, if Mary who lives in Australia wants to buy a backpack from Joe who lives in China using Joes Backpacks Shop, shell have to pay for the product using an intermediary like Paypal or her bank. Then that intermediary will move the money from Marys account to Joes account. On one hand, the bank usually takes a few days because it must carefully verify that it was a secure transaction. This is slow and risky. On the other hand, Paypal is fast but they take an important fee for every transaction. What if the bank goes bankrupt and loses everybodys money? What if the bank decides that Mary cant send money to Joe because they live in different countries? Why do we have to trust some middleman to take care of a personal transaction and lose time and money paying random fees? Fortunately, theres a better solution using the Ethereums blockchain. The blockchain is a public database where all the transactions are store and anybody can see them. That database stores new information o Continue reading >>

Deploy Your First Ethereum Smart Contract On A Blockchain!

Deploy Your First Ethereum Smart Contract On A Blockchain!

Deploy Your First Ethereum Smart Contract on a Blockchain! Understanding the concepts behind a blockchain is not as hard as one could imagine. Of course some specific concepts of a blockchain environment are harder to understand (e.g. mining) but I will try first to give you a simple introduction to the most important concept of blockchain. Then we will write a first smart contract inside a blockchain. That will be the first step before trying to build a decentralized web application implementing smart contracts! Basically a blockchain is a chain of block, more precisely a linked chain of blocks. A block is one element of a blockchain and each block has a common structure. The security of a blockchain is assured by its decentralized nature. Unlike a classic database, a copy of the blockchain is stored in each node of its peer-to-peer network. In the case where the local version of a blockchain in a networks node were corrupted, all the other nodes of the P2P network would still be able to agree on the actual value of the blockchain: thats the consensus. In order to add a fraudulous transaction to a blockchain, one should be able to hack half of the user of the network. Furthermore, it is also very hard to alter even only a local version of a blockchain because of a block structure. What is interesting in the concept of blockchain is that we can store any kind of data with very high security. Data is stored inside a block that contains several elements: An index (number of the block in the chain) A nonce (an integer that will be used during the mining process) If you are not familiar with the concept of hash, the important things to know are: From a very large departure set (typically infinite and very diverse), a hash function gives back a string of fixed length Given Continue reading >>

Everything You Wanted To Know About Blockchainsafter You Read That Other Great Article About Blockchains

Everything You Wanted To Know About Blockchainsafter You Read That Other Great Article About Blockchains

What is a blockchain? How do they work? The first of a two-part series. Read it? Cool. In that article we learned about hashes, their properties and how they can help us add security and verifiability to our data structures, in the form a a blockchain. We also stepped through a worked example of a blockchain's resilience to tampering with my good self playing the part of a villainous digital thief. This time, we'll build on that slightly contrived example and look at how blockchains can and do provide very real security and accountability, not just in financial transactions but in more generalised digital dealings. This'll take us through the grand-daddy of blockchains, Bitcoin, all the way to Ethereum, the blockchain that's currently doing its best to shake up governance and investments worldwide. It's a wild ride, but as always you've got this. Relax, learn, and by the time we're finished you'll be a font of delicious blockchainy knowledge. We're going to jump right in and learn about Bitcoin, since I know that's half the reason you're here. Before I can really define Bitcoin for you, though, we need to learn about a couple of concepts. Cast your mind back to the example at the end of the previous article. The setup was this: a bank stores its transaction information in a blockchain, and I (a thief) managed to get access to one of the blocks, perhaps on file somewhere. I modified that block to forge a new transaction that gave me lots and lots of money, but I didn't get away with it thanks to the blockchain's hash mechanism ensuring data integrity. However, if you thought to yourself "this doesn't seem like a particularly realistic situation", you weren't wrong. Let's try to flesh this out into a more believable context. We'll call it XYZCoin, with the symbol "XYZ" - Continue reading >>

Where And How Application Data Is Stored In Ethereum?

Where And How Application Data Is Stored In Ethereum?

Where and how application data is stored in Ethereum? Ethereum can host decentralized applications, DAPPs. These applications exist through small programs that live on the Blockchain: Smart Contracts. But when I write a Smart Contract, where is my application data Stored? We want to understand how data storage works before working on this platform. Code execution, servers and programming language are rarely critical to the design of an application. But the Data, its structure, and its security will constrain most of our design. Lets imagine we are porting apps to Ethereum: For a Facebook-like, where are the publications and comments data? For a Dropbox-like, where are my private files? Or for a Slack-like chat app, where do we store discussion channels? What about Private Messages? Were going to forget about the Blockchain for a minute: we already know its a machine that generates Consensus . We can forget the Blockchain and assume that Ethereum is a big, slow, reliable, computer. Were looking at the Ethereum System from a higher level of abstraction: the Software part. Ethereum holds a set of accounts. Every account has an owner and a balance (some Ether). If I prove my identity, I can transfer Ether from my account to another. The money will flow from one account to the other. Its an atomic operation called a Transaction. The Ethereum Software is a Transaction Processing System: 1. We have a state: the set of all accounts and their balance, 3. We get a new state: an updated set of accounts and their balances. Today we look into the ability to execute code and programs within a transaction. Thats where Smart Contracts come into play. Every account has an owner and a balance. But some of these accounts are special; they own themselves. At creation time, we give them a Continue reading >>

How Ethereum Works - Coindesk

How Ethereum Works - Coindesk

CoinDesk Launches 2017 Year in Review Opinion and Analysis Series Now that we've covered what ethereum is, let's dive deeper into how the platform functions under the hood. Consider the online notebook application described in " What is Ethereum? " Using ethereum, the appdoesn't require one entityto store and control its data. To accomplish this, ethereum borrows heavily from bitcoin's protocol and its blockchain design, but tweaks it to support applications beyond money. Ethereum aims to abstract away bitcoin's design, however, so that developers can create applications or agreements that have additional steps, new rules of ownership, alternative transaction formats or different ways to transfer state. The goal of ethereum's 'Turing-complete' programming language is to allow developers to write more programs in which blockchain transactions could govern and automate specific outcomes. This flexibility is perhaps ethereum's primary innovation, as explained in the guide " How Ethereum Smart Contracts Work ". The structure of the ethereum blockchain is very similar to bitcoin's, in that it is a shared record of the entire transaction history. Every node on the network stores a copy of this history. The big difference withethereum is that its nodes store the most recent state of each smart contract, in addition to all of the ether transactions. (This is much more complicated than described, but the text below should help you get your feet wet.) For each ethereum application, the network needs to keep track of the 'state', or the current information of all of these applications, including each user's balance, all the smart contract code and where it's all stored. Bitcoin uses unspent transaction outputs to track who has how muchbitcoin. While it sounds more complex, the id Continue reading >>

Calculating Costs In Ethereum Contracts

Calculating Costs In Ethereum Contracts

Thinking, coding, and explaining Ethereum and blockchain technologies. GAS PRICE PSA (20170823): The median gas price at the time of writing this article was 28 Gwei, and continues to be in the realm of 20 Gwei. This is far greater than the typical average and safe-low found on EthGasStation (4 and 0.5 Gwei respectively). The median is so high because of bad gas-price defaults found in many wallets. I highly recommend using EthGasStations average gas-price or lower in order to not pay high fees and to help drive down the market rate for gas-price. UPDATE (2017096): I ported the Google Spreadsheet of OPCODES to a github repo . This repo will be maintained and updated as the yellow paper evolves. What are users storing when they hold Ether? In one sense, they are storing the ability to perform computation on the Ethereum network. This computation is done in a decentralized fashion: A miner executes the computation associated with each transaction being included in a block, resulting in an updated state. Upon successfully mining a block, a miner broadcasts the block to the network. Each of the other miners and non-mining nodes verify the validity of the transactional computation and resulting state change before accepting the block as valid, incorporating the block into their copy of the blockchain, and moving on to the next block. You may have noticed that there is incredible amount of redundancy for every bit of computation on the network. Namely, each node verifies the results of each transaction read: every node runs all of the computation. Ive been researching Ethereum and other blockchain application platforms for a long time now, and rarely, if ever, do people outright say this. Once you get into the more technical side of things, it becomes an obvious feature of t Continue reading >>

Create A Hello World Contract In Ethereum

Create A Hello World Contract In Ethereum

Building a smart contract using the command line This page will help you build a Hello, World contract on the ethereum command line. If you don't know how to use the command line we recommend you skip this tutorial and instead build a Custom token using the graphical user interface . Smart contracts are account holding objects on the ethereum blockchain. They contain code functions and can interact with other contracts, make decisions, store data, and send ether to others. Contracts are defined by their creators, but their execution, and by extension the services they offer, is provided by the ethereum network itself. They will exist and be executable as long as the whole network exists, and will only disappear if they were programmed to self destruct. What can you do with contracts? Well, you can do almost anything really, but for our getting started guide let's do some simple things: To start you will create a classic "Hello World" contract, then you can build your own crypto token to send to whomever you like. Once you've mastered that then you will raise funds through a crowdfunding that, if successful, will supply a radically transparent and democratic organization that will only obey its own citizens, will never swerve away from its constitution and cannot be censored or shut down. And all that in less than 300 lines of code. Before you begin: Install the Ethereum CLI Learn more about contracts Please confirm that the GUI is closed before entering the geth console.Run geth to begin the sync process (this may take a while on the first run). Now that youve mastered the basics of Ethereum, lets move into your first serious contract. The Frontier is a big open territory and sometimes you might feel lonely, so our first order of business will be to create a little aut Continue reading >>

How To Learn Solidity: The Ultimate Ethereum Coding Guide

How To Learn Solidity: The Ultimate Ethereum Coding Guide

How To Learn Solidity: The Ultimate Ethereum Coding Guide Angel Investors, Startups & Blockchain developers... This Guide will walk you step -by-step in learning Solidity. The Ethereum Foundation has been shaking up the world of blockchain since the early days of the project, around late 2013 and early 2014. Ethereum really kickstarted the Bitcoin 2.0 and what we think of as the blockchain movement, after the first big Bitcoin bubble up past $1000 USD on the markets got everyones attention. Ethereum is a blockchain project with a cryptocurrency, Ether, similar to Bitcoin, but Ethereum has the added feature of a (nearly) Turing- complete virtual machine language and processing capability embedded into the node implementation. The Ethereum Virtual Machine (EVM) allows Ethereum nodes to actually store and process data in exchange for payment, responding to real-world events and allowing a lot of new opportunities to support on-chain applications that were never before available to developers and real-world users. I had the luck to actually be in Switzerland in early 2014, and to get to visit an Ethereum holon and hang out with some of the Ethereum founders before the Ether token sale, back when they were self-funded. I asked Mihai Alisie what an Ethereum smart contract is, and he explained: Smart-contracts are a way for people all across the globe to do business with each other even if they dont speak the same language or use the same currency. So thats really the perspective I begin with, the idea that we can define programmatically the rules of a business contract, in a simple machine language, to bring people together and allow them to conduct business in a trustable, secure, and automated fashion. Solidity Language itself is a tool that we use to generate machine-leve Continue reading >>

How Can Blockchain Be Used As A Database To Store Data?

How Can Blockchain Be Used As A Database To Store Data?

How can blockchain be used as a database to store data? Currently decentralized blockchain applications have few options to store data. Decentralized storage options are: Decentralized cloud file storages, such as Storj, Sia, Ethereum Swarm, etc. Distributed Databases, such as Apache Cassandra, Rethink DB, etc. Storing everything in blockchain itself: Storing everything in blockchain is the simplest solution. Currently most of the simple decentralized applications work exactly this way. However, this approach has significant drawbacks. First of all transactions to blockchain are slow to confirm. It may seem to be fast for money transfer (anyone can wait a minute), but it is extremely slow for a rich application data flow. Rich application may require many thousands transactions per second. Secondly, it is immutable. The immutability is the strength of blockchain that gives it high robustness but it is a weakness for a data storage. User may change their profile or replace their photo, still all the previous data will sit in blockchain forever and can be seen by anyone. The immutability results in one more drawback - the capacity. If all the applications would keep their data in blockchain, the blockchain size will grow rapidly, exceeding publicly available hard drive capacity. Full nodes can require special hardware. It may result in dangerous centralization of blockchain. Thats why storing data in blockchain only is not a good option for a rich decentralized application. Peer to peer file system, such as InterPlanetary File System. IPFS allows to share files on client computers and unites them in the global file system. The technology is based on BitTorrent protocol and Distributed Hash Table. There are several good moments. It is really peer to peer - to share anythi Continue reading >>

How Can I Retrieve The Data From Block In Ethereum Blockchain?

How Can I Retrieve The Data From Block In Ethereum Blockchain?

I did one small event registration smart contract (By using solidity()) in that I purchased a ticket for an event by giving the details of my email id and no.of tickets I want. Finally, I want to know how can I get back what are the details I was given. I am using testrpc, truffle, and private net.After clicking on purchase I got these details in tetrpc terminal Transaction: 0x35e92857102b0dbacd43234d1ea57790405eb9bef956b245c6b7737bc23d011b Gas usage: 106532 Block Number: 5 Block Time: Sat Feb 03 2018 12:05:57 GMT+0530 (IST) [email protected]:~/EventRegistration-POC/EventRegistration$ truffle consoletruffle(development)> web3.eth.getTransaction('0x35e92857102b0dbacd43234d1ea57790405eb9bef956b245c6b7737bc23d011b'){ hash: '0x35e92857102b0dbacd43234d1ea57790405eb9bef956b245c6b7737bc23d011b', nonce: 4, blockHash: '0x7c790dae57babfe40d68d8aad94913c2b748501c5734aec86cc3fcf0afc4f154', blockNumber: 5, transactionIndex: 0, from: '0x031e060414a0d2573f5b10bc75c0894d72288292', to: '0xa88a366e888bbccfb78092957ffc7760bc7c6db1', value: BigNumber { s: 1, e: 18, c: [ 60000 ] }, gas: 200000, gasPrice: BigNumber { s: 1, e: 0, c: [ 1 ] }, input: '0xa28f161c00000000000000000000000000000000000000000000000000000000000000400000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000000b6d40676d61696c2e636f6d000000000000000000000000000000000000000000' }truffle(development)> but I didn't get the details I was given while purchasing. Please tell me how can I do this? web3.eth.getTransaction(txHash) will returns transaction details like blockHash, transactionIndex, from, to, etc. It will take some time to miner to mine block and add to blockchain. So its not instant. If you want to know any storage value is added/modified in blockchain Continue reading >>

Create Your Own Marriage Contract

Create Your Own Marriage Contract

New to Ethereum? Try visiting this guide before moving forward. The online Solidity compiler has the ability to connect to running instances of your geth node through RPC and IPC. Below are the flags you need to add when you start geth in order to allow your node to communicate with the website. geth --unlock 0 --rpc --rpcport "8545" --ipcapi "admin,db,eth,debug,miner,net,shh,txpool,personal,web3" --rpcapi "db,eth,net,web3" --rpccorsdomain "console If you'd like to have access to the geth console in a second command prompt window, open another console window and enter geth attach to attach that console window to your geth instance. You may want to make a script so you can easily open your geth console. I accomplished this on my Windows system by creating a file called geth_unlocked.cmd which opens my geth console. Back at the Solidity Compiler website, we want to connect to our geth node over either RPC or IPC. Most people will want to connect over RPC. Click the Cube icon. Change the address and port in the "Web3 provider input" box to match the flags you set to launch geth. If you used the previous step to launch geth your address and port should be A dialog box may pop up warning you if you want to connect. Click "OK". Create Your Contract and Call Your Contract Functions Click the red "Create" button on below your node connection settings. Your transaction will soon be mined (normally within 30 seconds) and your public variables (in blue) and your functions (in red) will appear below. Add information to the function calls to create your marriage on the blockchain. Note that Ethereum doesn't always understand the difference between a string and a hex value, so this online compiler differentiates the two by using quotes. If you want to submit a string, surround that Continue reading >>

Accessing Contracts And Transactions

Accessing Contracts And Transactions

In previous sections we have seen how contracts can be written, deployed and interacted with. Now its time to dive in the details of communicatingwith the Ethereum network and smart contracts. An Ethereum node offers a RPC interface. This interface gives apps access to the Ethereumblockchain and functionality that the node provides, such as compiling smart contract code. It uses a subset of the JSON-RPC 2.0 specification (no support for notifications or named parameters) as serialisation protocol andis available over HTTP and IPC (unix domain sockets on linux/OSX and named pipes on Windows). If you are not interested in the details but are looking for an easy to use javascript library you can skip the following sections and continue with Using Web3 . The RPC interface uses a couple of conventions that are not part of the JSON-RPC 2.0 specification: Numbers are hex encoded. This decision was made because some languages have no or limited support for working with extremly large numbers. To preventthese type of errors numbers are hex encoded and it is up to the deverloper to parse these numbers and handle them appropriately. See the hex encoding section on the wiki for examples. Default block number, several RPC methods accept a block number. In some cases its not possible to give a block number or not very convenient. Forthese cases the default block number can be one of these strings [earliest, latest, pending]. See the wiki page for a list of RPC methods that use the default block parameters. We will go through the different steps to deploy the following contract using only the RPC interface. contract Multiply7 { event Print(uint); function multiply(uint input) returns (uint) { Print(input * 7); return input * 7; }} The first thing to do is make sure the HTTP RPC inter Continue reading >>

Ethereum Overview | Truffle Suite

Ethereum Overview | Truffle Suite

You may have heard the terms "blockchain" and "smart contract" floating around, but what do they actually mean? In this tutorial, we'll demystify the jargon, show you practical blockchain solutions, and give you direction on how to create an application that takes advantage of the blockchain. Blockchains are used when multiple parties, perhaps located across the world, need to share data and transfer value without trusting each other. The financial world describes this trust as the counterparty risk: the risk that the other party won't hold up their end of the bargain. Blockchains completely remove the counterparty risk through a revolutionary system of mathematics, cryptography, and peer-to-peer networking. Before we go into those details, let's first look at some history and how the need for blockchains arose. In the 1960's the first computerized databases emerged. With hardware occupying multiple rooms and the Internet decades away, data naturally existed in central, physical locations. This is a centralized approach, meaning the location and accessing of data is controlled by a central authority. Centralized systems can be manipulated, from inside or outside, so we have to trust the owners of these systems to have sufficient will and resources to keep their data secure and with integrity. Centralized databases are still the most common today, powering most of our online and offline applications. A self-hosted blog is a common example of a centralized database. The owner could potentially edit posts in hindsight or censor users without recourse. Alternately, a hacker could infiltrate the server and commit malicious acts. If there is no database backup, reversing the damage might be impossible. Graphically represented, each arrow crossing a boundary of the main serve Continue reading >>

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