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What Is A Nonce In Ethereum?

Neat Ethereum Tricks. The Transaction Nonce.

Neat Ethereum Tricks. The Transaction Nonce.

Neat Ethereum tricks. The transaction nonce. Neat Ethereum tricks. The transaction nonce. Whenever a user deploys a new contract to the Ethereum blockchain, that contract receives its own Ethereum address. User 0x0a Deploying contract Reclaim > contract address 0x0a1 As it turns out, these contract addresses ARE NOT a random address. The address of every contract well deploy depends on two parameters: The Ethereum address from which the contract is being deployed. The nonce of the transaction! Not to be confused with the nonce used in the mining process. In Ethereum, every transaction have a nonce associated with it. The nonce is one of the tools that helps to index and process transactions in the right order. The nonce itself IS NOT a random value. It grows by scalar one with every transaction we transmit to the blockchain. For the Ethereum test-net, the nonce begins with 0x100000 (1048576). The new contract address can be computed in the following way: def mk_contract_address(sender, nonce): return sha3(rlp.encode([normalize_address(sender), nonce]))[12:] sha3 and rlp and encryption functions. The only two variables are the address of the sender and the nonce (basically the transaction number for that particular address). Ive installed the pyethereum library on ubuntu 16.04. and changed dir to directory cd /pyethereum/ethereum . There I launched python 2.7.12 and imported the utils. $ cd/pyethereum/ethereum$ python>> import utils Than I used the functionutils.mk_contract_address(sender address, nonce) to get the addresses of my future contracts. For the sender address: 0x43CCFE27708381164Fd079556C7Ef158A6d409DcI can check for what the address of the next deployed contract will be. nonce1 =1048576 =>; 0x7930935a32ee489bd102002c2598602ff79c24fdnonce2 =1048577 =>; 0x0d7 Continue reading >>

What Does Each Genesis.json Parameter Mean?

What Does Each Genesis.json Parameter Mean?

nonce A 64-bit hash, which proves, combined with the mix-hash, that a sufficient amount of computation has been carried out on this block: the Proof-of-Work (PoW). The combination of nonce and mixhash must satisfy a mathematical condition described in the Yellowpaper, 4.3.4. Block Header Validity, (44), and allows to verify that the Block has really been cryptographically mined and thus, from this aspect, is valid. The nonce is the cryptographically secure mining proof-of-work that proves beyond reasonable doubt that a particular amount of computation has been expended in the determination of this token value. (Yellowpager, 11.5. Mining Proof-of-Work). timestamp A scalar value equal to the reasonable output of Unix time() function at this block inception. This mechanism enforces a homeostasis in terms of the time between blocks. A smaller period between the last two blocks results in an increase in the difficulty level and thus additional computation required to find the next valid block. If the period is too large, the difficulty, and expected time to the next block, is reduced. The timestamp also allows verifying the order of block within the chain (Yellowpaper, 4.3.4. (43)). mixhash A 256-bit hash which proves, combined with the nonce, that a sufficient amount of computation has been carried out on this block: the Proof-of-Work (PoW). The combination of nonce and mixhash must satisfy a mathematical condition described in the Yellowpaper, 4.3.4. Block Header Validity, (44). It allows to verify that the Block has really been cryptographically mined, thus, from this aspect, is valid. difficulty A scalar value corresponding to the difficulty level applied during the nonce discovering of this block. It defines the mining Target, which can be calculated from the previous Continue reading >>

Creating Offline Ethereum Transactions In Javascript

Creating Offline Ethereum Transactions In Javascript

Creating offline Ethereum transactions in JavaScript By Mikko Ohtamaa a year ago. Tagged under ethereum , javascript , web3 , etherscan . In this blog post we show how to create Ethereum blockchain transactions programmatically in JavaScript and offline. This is the second part of tutorial blog posts continuing the earlier Ethereum JavaScript tutorial left. We bend the meaning of the word offline here a bit. We still communicate with Ethereum network to get the gas cost and the next transaction nonce. However, the private key never leaves the computer. This blog post serves mostly as an example. Advanced users can use the script presented here for doing Ether cold wallet and offline transactions. Target address, either a contract or an Ethereum account. Nonce, incremented once per transaction per account, to prevent double spend attacks. Value, how many Ethers are transferred. Can be 0 for contract calls, but you still need to pay for the gas. The maximum gas the transaction is allowed pull from the sending account. The gas price if the transaction needs a preferential treatment. Optional data payload that would include any function call and arguments encoded. Transaction is signed with the private key of the sending account address. Based on these arguments you can create a raw transaction, as a hex string, that can be pushed to the network. Pushing can happen either through EtherScan.io service or through web3.eth.sendRawTransaction API. Furthermore in this particular example we also need EtherScan.io API key - we use their API to communicate with the network The example script is available on TokenMarket Github repository . Install dependencies with NPM - see previous blog post Please note that this command line monster will go away in the future when Node.js starts Continue reading >>

Glossary Ethereum/wiki Wiki Github

Glossary Ethereum/wiki Wiki Github

See also: Computational infeasibility: a process is computationally infeasible if it would take an impracticably long time (eg. billions of years) to do it for anyone who might conceivably have an interest in carrying it out. Generally, 280 computational steps is considered the lower bound for computational infeasibility. Hash: a hash function (or hash algorithm) is a process by which a piece of data of arbitrary size (could be anything; a piece of text, a picture, or even a list of other hashes) is processed into a small piece of data (usually 32 bytes) which looks completely random, and from which no meaningful data can be recovered about the document, but which has the important property that the result of hashing one particular document is always the same. Additionally, it is crucially important that it is computationally infeasible to find two documents that have the same hash. Generally, changing even one letter in a document will completely randomize the hash; for example, the SHA3 hash of "Saturday" is c38bbc8e93c09f6ed3fe39b5135da91ad1a99d397ef16948606cdcbd14929f9d, whereas the SHA3 hash of Caturday is b4013c0eed56d5a0b448b02ec1d10dd18c1b3832068fbbdc65b98fa9b14b6dbf. Hashes are usually used as a way of creating a globally agreed-upon identifier for a particular document that cannot be forged. Encryption: encryption is a process by which a document (plaintext) is combined with a shorter string of data, called a key (eg. c85ef7d79691fe79573b1a7064c19c1a9819ebdbd1faaab1a8ec92344438aaf4), to produce an output (ciphertext) which can be "decrypted" back into the original plaintext by someone else who has the key, but which is incomprehensible and computationally infeasible to decrypt for anyone who does not have the key. Public key encryption: a special kind of encr Continue reading >>

Ethereum Blockchain Transaction. How?

Ethereum Blockchain Transaction. How?

The focus of this post is primarily on signing transaction offline and on making Ethereum contract calls, but in the process I would make a one liners onunderstanding of Blockchain in general and what is Ethereum? Blockchain is a simple ledger accessible by anyone, it is immutable(unchangeable). What else we need to know. Oh ya...lots of crypto stuff going on. Thats all I know...don't judge me! What is Ethereum and What makes it different? Ethereum is again a blockchain(You already knew that...din't you?). Anyways, Ethereum has something named "contract". Don't get scared, it is another piece of code which will be executed every time you will make acall to "contract"(Yes, We are getting to the point in a moment). What is contract and How Would I Make A Contract? Oh Boy, You will need to know that. As far as what a contract is?, below statement can explain a bit. "contract is a piece of code which controls the execution of transactions on the blockchain facilitating the functionalities of your application." and how to write one? you can find it here . If you are done reading the above link then it's awesome or else you can do it whenever you want. a simple contract would look something like this. Contracts in ethereum are written in solidity. contract myContract(){ uint256 public balance = 100; function addBalance(unit _value){ balance += _value; return balance; }} I am taking an example of a static value, which is called balance. As you can see, the balance variable has has a public keyword and an initial value of 100(arbitrary value) , which means who ever has your contract address(Which is obtained when you deploy your contract to the ethereum blockchain) would be able to access your public balance. So how would you access your balance. It's very simple, you can just Continue reading >>

How Is A Block Hash Created?

How Is A Block Hash Created?

A Bitcoin hash is created by running the SHA-256 algorithm on six pieces of data. 3. The Merkle Root of all the transactions selected to be in that block. 1. The Bitcoin version number is simply a n umber to track software and protocol upgrades . 2. The previous block hash is the hash of the parent block in the blockchain . i.e. block 23s hash if this is block 24. 3. The Merkle Root or essentially a binary hashing of all the transactions in the block . 4. The timestamp is the time that hashing took place. 5. The difficulty target is the Bitcoin Network targeted number of zeroes. 6. The Nonce is a 32Bit number that the miners vary from 0 to try and find the hash solution. As the Bitcoin mining network has advanced from Mega hashes to Giga Hashes to Peta hashes the nonce, or the number that the miner varies can be run through in less than a second, which has 4 billion attempts has become easily exceeded resulting in miners having to use an extra nonce factor. They got around this by adding data into the coinbase transaction (generation transaction) which then means, after recalculating, the normal nonce numbers can be run through again, and if run through in a second before the timestamp changes, the Merkle root is recalculated and run through again. Continue reading >>

Ethereum's Memory Hardness Explained, And The Road To Mining It With Custom Hardware

Ethereum's Memory Hardness Explained, And The Road To Mining It With Custom Hardware

Ethereum's Memory Hardness Explained, and the Road to Mining It with Custom Hardware Ethereum's Memory Hardness Explained, and the Road to Mining It with Custom Hardware As crypto-currencies increase in value, so does the payout from mining them. This creates a substantial economic incentive to not only deploy more mining hardware, but to also develop faster, more efficient mining hardware. We saw this with bitcoin: Mining migrated from CPUs, to GPUs, to FPGAs, and now to ASICs [1] . Today, Ethereum GPU mining is the norm, but the miners havent made the jump to running the ethereum mining/hashing algorithm, ethash, on specialized hardware solutions (e.g. FPGAs and ASICs). Plenty of articles and forums attribute this to ethash being memory hard (a.k.a. memory bound ). Here, Ill walk through where Ethereum minings memory hardness comes from, and what the next generation of custom ethereum mining hardware might look like. For this article, Im assuming readers have a general understanding of standard computer technologies and crypto-currency blockchains, but dont need to be programming or mining experts. For a more technical, programmer-oriented explanation of Ethereums mining algorithm, called ethash, please refer to the ethash page on the ethereum wiki . For a less technical introduction to blockchains, visit the blockgeeks blockchain guide here . In proof-of-work mining, miners are tasked with generating a short binary blob (called a nonce), which, when hashed, produces an output value less than a pre-specified target threshold. Due to the cryptographic nature of each currencys hash function, there is no way to reverse-engineer or back-compute a nonce that satisfies the target threshold limit. Instead, miners must guess-and-check hashes as fast as possible, and hope the Continue reading >>

What You Should Know About Nonces And Difficulty

What You Should Know About Nonces And Difficulty

This is the sixth in a series of posts where we discuss the core concepts behind the Blockchain, Bitcoin and Ethereum. At Verify, were building a reputation protocol on the Ethereum blockchain and are sharing these posts in an effort to share our knowledge with the wider crypto community. In Ethereum ABC , we introduced the accounts fields. We mentioned the nonce field, but never explained it. This post will dive into that. Every transaction in Ethereum has what is called a nonce. We first saw the word nonce in our talk about Bitcoins mining , used to find proof of work; is it the same nonce in Ethereum transactions? Let us look into this question. In Ethereum there is a nonce for the block, which is similar to what we have been introduced to in Bitcoin. There is also a noncefor every transaction (in external accounts). It is the number of transactions made or sent from a given address. Whenever you send a transaction the nonce is incremented by one. The reason for a nonce in a transaction is to ensure: You may have already guessed why this is important. Well, you guessed right: it is to prevent double-spends. Consider an example where: you send out a transaction with normal GASPRICE, when it is waiting to be added by some miner you send out another transaction with high GASPRICE to have the second mined before the first, making the first transaction invalid. That is why you have a nonce in Ethereum transactions, double-spends can never happen. A transaction of nonce 2 can never be mined before a transaction of nonce 1. Also note that a nonce cant be skipped. Meaning if you sent out a transaction with nonce 3 without sending nonce 2 that cant work. Nonces need to be sequential and in order, no skips. What about contracts? They are a type of account so they too have a n Continue reading >>

Making Sense Of Ethereum Nonce(sense)

Making Sense Of Ethereum Nonce(sense)

Experienced Software Engineer. Senior Android Engineer @ Kik We expect users to send multiple Kin transactions in a row. Were not expecting users to understand blockchain and monitor their transactions manually. When testing our Kin wallet SDK ( Android and iOS ), we witnessed a problem sending multiple transactions one after the other. In a specific period of time, all of our transactions got stuck we couldnt see that they were pending, and eventually they were cancelled. As it turns out, transactions had the same nonce for multiple transactions. Proof of work nonce: A meaningless value in a block that can be adjusted in order to try to satisfy the proof of work condition. This is the essence of mining. This value makes satisfying proof of work hard computational work that depends on luck. Account nonce: A transaction counter in each account that prevents replay attacks . For example, a transaction sending 20 coins from A to B can be repeated over and over by B to continually drain As balance. Our problem is related to the latter nonce the transaction counter. When making a transaction in Ethereum, a consecutive number should be attached to each transaction on the same account. Each node will process transactions from a specific account in a strict order according to the value of its nonce. Therefore, failing to increment this value correctly can result in different kinds of errors. For instance, lets say the latest transaction nonce was 121: Reusing nonce: if we send a new transaction for the same account with a nonce of either 121 or below, the node will reject it. Gaps: if we send a new transaction with a nonce of either 123 or higher, the transaction will not be processed until this gap is closed, i.e. until a transaction with nonce 122 has been processed. As ment Continue reading >>

Cancel Pending Transactions On Ethereum

Cancel Pending Transactions On Ethereum

Oct 9, 2017 00:23 695 words 4 minutes read ethereum pending transaction geth Ethereum transactions model is vastly different from Bitcoin. Instead of using UTXO (unspent transaction outputs)transaction uniqueness and order are achieved using transaction nonce. It is an integer (uint256) counter whichis incremented for each transaction of an account. Its value is effectively the number of transactions sent from a given address andits value must be included in every transaction. transactions must be processed in order (transaction with a nonce of 1 must be processed before the transaction with a nonce of 2) no skipping (transaction with a nonce of 4 cannot be included in a block until transactions with nonces of 1, 2, 3 are processed) This way the network is able to identify duplicates of transactions and enforce their order (which is essential for smart contracts). Each transaction must set gas price which directly affects transaction fees.Miners optimize their profits by including transactions with a high gas price first. If gas price is low the transaction will wait for a long time until it is mined.Eventually, it will be mined (sometimes many hours later) or dropped (miners have limited resources to queue pending transactions).However, even if the transaction is dropped by miners it may still await in pendingTransaction list of your client and artificially increaseyour nonce. You can explore the list of pending transactions on Etherscan . When a transaction is waiting for being mined all subsequent transactions are blocked. They cannot be included in a blockuntil the previous one is included (it is determined by mentioned nonce value). Even if subsequent transactions havea very high gas price they cannot be processed as it would break the order of transactions and pr Continue reading >>

Transactions - What Is Nonce In Ethereum? How Does It Prevent Double Spending? - Ethereum Stack Exchange

Transactions - What Is Nonce In Ethereum? How Does It Prevent Double Spending? - Ethereum Stack Exchange

What is nonce in Ethereum? How does it prevent double spending? recently I got fascinated by blockchain, and started learning Ethereum. I came across Concept of the nonce in Ethereum. After researching I found out that nonce is used for two purposes a. To keep transaction related to an account in order. i.e if there is a transaction with nonce 3 related to some account in the txpool and some transaction will nonce 4 arrived then that transaction won't be mined until and unless transaction with nonce 3 is mined. But I have some question that I am not able to find? i) nonce value is related to an address, right? So two address can have same nonce at the same time i.e. account with Address A can have the latest nonce 2 similarly account with address B can also have latest nonce 2. ii) Do all nodes in the network will have same latest nonce value for all accounts available in the network? That is, if there are three accounts and 2 miners then and nonce value for three accounts are 1,2,3 respectively, then both miner will have the same nonce. b) how is nonce used to prevent a double spend? If you refer the Glossary at Github Wiki , there are two types of nonce used in Ethereum. Account nonce - It's simply the transaction count of an account Proof of work nonce - The random value in a block that was used get the proof of work satisfied (depending on the difficulty at the time). Here you are referring to the account nonce, which is the transaction count from that account. i)Nounce value is related to an address right?So two address can have same nounce at the same time i.e account with Address A can have latest nounce 2 similarly account with address B can also have latest nounce 2. Yes as explained above, it's the transaction count and hence it's related to the account. And 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 >>

The Question Of Mining

The Question Of Mining

There are a lot of interesting changes to the Ethereum protocol that are in the works, which will hopefully improve the power of the system, add further features such as light-client friendliness and a higher degree of extensibility, and make Ethereum contracts easier to code. Theoretically, none of these changes are necessary; the Ethereum protocol is fine as it stands today, and can theoretically be released as is once the clients are further built up somewhat; rather, the changes are there to make Ethereum better. However, there is one design objective of Ethereum where the light at the end of the tunnel is a bit further: mining decentralization. Although we always have the backup option of simply sticking with Dagger, Slasher or SHA3, it is entirely unclear that any of those algorithms can truly remain decentralized and mining pool and ASIC-resistant in the long term (Slasher is guaranteed to be decentralized because its proof of stake, but has its own moderately problematic flaws). The basic idea behind the mining algorithm that we want to use is essentially in place; however, as in many cases, the devil is in the details. This version of the Ethereum mining algorithm is a Hashcash-based implementation, similar to Bitcoins SHA256 and Litecoins scrypt; the idea is for the miner to repeatedly compute a pseudorandom function on a block and a nonce, trying a different nonce each time, until eventually some nonce produces a result which starts with a large number of zeroes. The only room to innovate in this kind of implementation is changing the function; in Ethereums case, the rough outline of the function, taking the blockchain state (defined as the header, the current state tree, and all the data of the last 16 blocks), is as follows: Let h[i] = sha3(sha3(block_head Continue reading >>

Ethereum Transaction : What Is Nonce ?

Ethereum Transaction : What Is Nonce ?

In Ethereum, every transaction has a nonce. The nonce is the order of transactions sent from a given address. Each time you send a transaction, the nonce increases by 1. There are rules about what transactions are valid transactions and the nonce is used to enforce some of these rules. Specifically: Transactions must be in Order: You cannot have a transaction with a nonce of 1 mined before one with a nonce of 0. No Skipping! You cannot have a transaction with a nonce of 2 mined if you have not already sent transactions with a nonce of 1 and 0. This field prevents double-spends as the nonce is the order the transactions go in. In order for a double-spend to be "successful", you typically... Collect something in return from this first transaction Quickly send another transaction with a high gas price Have this second transaction mined first, therefore invalidating the first transaction. This is why exchanges wait for you to have a certain number of confirmations before allowing you to trade freshly-deposited funds. In Ethereum, this method of "double-spending" is not possible because each transaction has a nonce included with it. Even if you attempt to do the above, it will not work as the second transaction (nonce of 3) cannot be mined before the first transaction (nonce of 2). Continue reading >>

Ethereum Quirks And Vulns

Ethereum Quirks And Vulns

Ive continued diving deep into the mechanics of Ethereum, previously finding vulnerabilities in python client and the Go and C++ clients as well as insecure contracts . Lately, Ive come across a few interesting quirks as well as some more vulnerabilities. There are two types of accounts within Ethereum; normal accounts and contract accounts. Contracts are created by sending transactions with empty to-fields, and contain some data which is executed (ala constructor) and, hopefully, returns some code which gets placed on the blockchain. The contracts are, naturally, part of the same address space as the normal accounts; and the address of a contract is determined thus : address = sha3(rlp_encode(creator_account, creator_account_nonce))[12:] This is fully deterministic; for a given account, say, accountA is 0x6ac7ea33f8831ea9dcc53393aaa88b25a785dbf0, the addresses that it will create are the following: nonce0= "0xcd234a471b72ba2f1ccf0a70fcaba648a5eecd8d"nonce1= "0x343c43a37d37dff08ae8c4a11544c718abb4fcf8"nonce2= "0xf778b86fa74e846c4f0a1fbd1335fe81c00a0c91"nonce3= "0xfffd933a0bc612844eaf0c6fe3e5b8e9b6c1d19c" This is a bit interesting; it means that these can be used to hide money. From accountA, we can send ether to e.g. the nonce1-address. At this address, the ether will be unrecoverable, until we first make a transaction (increasing accountA nonce to 1) and then create a contract which lands on nonce1 and thus becomes the owner of the money; and can send it back again. Furthermore, it would be possible to not just hide money in vertical mode via nonce, but also horizontally by deeper levels of contracts: nonce+3 --> contract3 nonce+2 nonce+1 nonce+2 --> contract1 --> contract2 : nonce nonce+1`accountA` : nonce The operation above could be expressed as up,up, in, in, up,u Continue reading >>

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