What The Heck Is Utxo Peeking Into The Bitcoin Transaction

As you can see from the tables, with P2SH the complex script that details the conditions for spending the output is not presented in the locking script. Instead, only a hash of it is in the locking script and the redeem script itself is presented later, as part of the unlocking script when the output is spent. This shifts the burden in fees and complexity from the sender to the recipient of the transaction. Every bitcoin client will validate transactions by executing the locking and unlocking scripts together. For each input in the transaction, the validation software will first retrieve the UTXO referenced by the input. That UTXO contains a locking script defining the conditions required to spend it. The validation software will then take the unlocking script contained in the input that is attempting to spend this UTXO and execute the two scripts. Whenever you spend your bitcoins, the public key behind the bitcoin address from which the bitcoins are sent is revealed. Fortunately, for all practical purposes it is currently not possible for anyone to calculate a private key from a public key. The reason being that a public key is calculated from the private key using elliptic curve multiplication, which is a mathematical formula that can only be calculated in one direction.

unspent transaction output

The proof of work used in Bitcoin takes advantage of the apparently random nature of cryptographic hashes. A good cryptographic hash algorithm converts arbitrary data into a seemingly random number. If the data is modified in any way and the hash re-run, a new seemingly random number is produced, so there is no way to modify the data to make the hash number predictable. Outputs are tied to transaction identifiers , which are the hashes of signed transactions.


While you may see a single balance in your crypto wallet, it is actually made up of ‘change’ from other transactions. First, transactions conducted on a blockchain also require the payment of transaction fees, which are deducted from the amount of change you get in return – unlike when paying in cash. These outputs, whilst ‘unspent’, are not included in the UTXO set, as they are provably unspendable and will never be needed to validate a future transaction. Prior to the Genesis upgrade in February 2020, one form of these outputs start with the OP_RETURN opcode in the ScriptPubKey field of a transaction. Prior to this upgrade, The OP_RETURN opcode ended the script execution and returned a failure. After the Genesis upgrade, this provably unspendable output will be unlocking scripts beginning with the opcodes OP_FALSE OP_RETURN. When a node receives a new transaction, one of the checks on the transaction is if the input is spending a UTXO in the set.

unspent transaction output

Depending upon the semantics of these structures the data within them are interpreted by the protocol. A bitcoin on-chain metric has increased to three-year highs, suggesting a potential supply shortage and low odds of significant price pullback. While there are conflicting interpretations about this latest signal, many market observers are taking it to be positive for the cryptocurrency. The UTXO set is the comprehensive set of all UTXOs existing at a given point in time. The sum of all UTXOs will yield the precise current supply of Bitcoin. Before going further into how a UTXO works, we have to understand first how bitcoin transactions are designed. The first ever block recorded on its respective blockchain network, also referred to as Block 0 or Block 1.

Node Storage Solutions

If it still fails, the transaction will the Failed to broadcast status. Note that if the recalculated fees were higher than ETH 0.005, the transaction would have been broadcasted with that amount. The available balance is calculated differently depending on the crypto asset. CryptoDefinitions is one of the most comprehensive blockchain and cryptocurrency dictionaries on the web.

Operators push or pop one or more parameters from the stack, act on them, and might push a result onto the stack. For example, OP_ADD will pop two items from the stack, add them, and push the resulting sum onto the stack. If you forget to add a change output in a manually constructed transaction, you will be paying the change as a transaction fee. Transaction fees serve as an incentive to include a transaction into the next block and also as a disincentive against “spam” transactions or any kind of abuse of the system, by imposing a small cost on every transaction. Transaction fees are collected by the miner who mines the block that records the transaction on the blockchain. A script that fulfills the conditions of the UTXO locking script. Strictly speaking, outputs come first because coinbase transactions, which generate new bitcoin, have no inputs and create outputs from nothing. As it stands today, the fact to keep all your UTXOs in a single bitcoin address does not heighten security risks.

Besides, the market mood is bullish, and holders are unlikely to book profits anytime soon. The existence of satoshis make Bitcoin divisible, a necessary trait for deflationary money. unspent transaction outputs or UTXOs serve as globally-accessible evidence that you have Bitcoin in your digital wallet. A seed phrase or menmonic seed is a collection of words that can be used to access your cryptocurrency wallet. The pseudonym of the creator or creators of the bitcoin protocol and whitepaper. Her only option here is to break up the 0.4 BTC unit and to send 0.3 BTC to Bob, and 0.1 BTC back to herself. She would normally reclaim less than 0.1 BTC due to mining fees, but let’s simplify and leave the miner out.

Therefore, the fact that your public key is exposed during a bitcoin transaction, does not heighten the risk of your private key being discovered in the future. It follows that the remaining UTXOs in that same bitcoin address remain as secure as before the public key was exposed. It follows from the above that bitcoin transactions do not refer to an account or someone’s identity. The output of the bitcoin transaction, are newly created locked UTXOs registered to the receiving bitcoin address. Double-spend attack A double-spend attack is often considered the primary attack vector against blockchain based cryptocurrencies.

This mainly happens due to the protocol rules which Satoshi Nakamoto had defined in Bitcoin to prevent double spending. Also, there is no way in the bitcoin world to spend partial amounts while completing a transaction. The transaction logic is simplified as each UTXO can only be consumed once and as a whole. Because the logic is simpler, transaction verifications can be made parallel. Different schemes of privacy-enhancing techniques can be developed using the UTXO model, like coin-join, etc. UTXO model is inherently unintuitive thus most of the wallets had to abstract away the UTXOs and simulate normal account like UI for users. UTXOs are limited in terms of more exotic smart contracts that executes based on the user’s total account balance.

unspent transaction output

It should feel a little bizarre to think about this obscured concept of UTXO in a digital payment system. UTXO feels inherently similar to physical cash, whereas, in digital payment platforms, we deal with accounts. The account model is simply, where users have one or multiple accounts, the amounts can be anything, and there is no concept of change back. As we have already mentioned, UTXOs are bitcoins, and they are represented in different ways by different wallets for user information. When you query a wallet for your bitcoin balance, the wallet in the backend unspent transaction output gathers up all the UTXOs that you own, and show you the sum of the value of these UTXOs. These calculations happen in the background and are abstracted away from users. Transaction graph historyFor example, in TX4 above, the input0 points back to output0 of TX2. The Outputs at the last transactions namely TX6 and TX3, the one with 10K and 20K values are the UTXOs. Because they have not yet been referred to by a transaction input. Once an input points at them and provides the correct key to open them, they are spent and are not considered UTXO anymore.

The parent Ethereum account must be credited to allow paying the gas fees of ERC20 transactions. You can consolidate up to 100 UTXOs at a time by creating a transaction to yourself. However, UTXOs which value falls below 546 satoshis are too small to be consolidated and will be ignored. It’s possible to create multiple transaction requests in an account. Transactions are broadcasted only when all approvals have been collected from the necessary Operators. If there were any changes, you can return to the previous simple transaction screen by clicking on the “Arrow” button as shown in the image below. ) rely on looking at UTXOs to determine certain patterns in economic activity on-chain. Despite these complexities, Glassnode is pioneering the process of applying UTXO-focused metrics to account-based chains.

Which of these fields is present in a Bitcoin block summary?

Description. Each block contains, among other things, the current time, a record of some or all recent transactions, and a reference to the block that came immediately before it. It also contains an answer to a difficult-to-solve mathematical puzzle – the answer to which is unique to each block.

Imagine a shopper buying a $1.50 beverage, reaching into her wallet and trying to find a combination of coins and bank notes to cover the $1.50 cost. The shopper will choose exact change if available , or a combination of smaller denominations , or if necessary, a larger unit such as a five dollar bank note. If she hands too much money, say $5, to the shop owner, she will expect $3.50 change, which she will return to her wallet and have available for future transactions. Once a bitcoin transaction is sent to any node connected to the bitcoin network, the transaction will be validated by that node.


For example, a purchase worth 1 bitcoin may retrieve 0.6 BTC from one byte and 0.4 BTC from another. Change from each of these fractions is then sent to the UTXO database to be spent at a later date. If the transaction gathers all of the required signatures, but the preceding conditions do not hold, the transaction’s outputs will not be valid and will not be accepted as inputs to subsequent transactions. When creating a new transaction, the output states that the transaction proposes do not exist yet, and must therefore be created by the proposer or proposers of the transaction. However, the input states already exist as the outputs of previous transactions. We therefore include them in the proposed transaction by reference. In the field of cryptocurrency trading, an Unspent Transaction Output pertains to the abstraction of electronic money. What each UTXO represents is a chain of ownership that is released and enacted as a chain of Digital Signatures.

This model was inspired from the bank’s record keeping of accounts, owner of accounts, and balance in those accounts. Each transaction has a number of transaction inputs, that is, a source of funds, and also has a number of transaction outputs, that is, where the funds go. Generally speaking, every transaction spends an input and generates an output, and the output it generates is the “unspent transaction output”, which is UTXO. A model comprising of inputs and outputs that determine how transactions are executed on the Bitcoin network. Another important part of the P2SH feature is the ability to encode a script hash as an address, as defined in BIP0013. P2SH addresses are Base58Check encodings of the 20-byte hash of a script, just like bitcoin addresses are Base58Check encodings of the 20-byte hash of a public key. P2SH addresses use the version prefix “5”, which results in Base58Check-encoded addresses that start with a “3”. For example, Mohammed’s complex script, hashed and Base58Check-encoded as a P2SH address becomes 39RF6JqABiHdYHkfChV6USGMe6Nsr66Gzw. Now, Mohammed can give this “address” to his customers and they can use almost any bitcoin wallet to make a simple payment, as if it were a bitcoin address. The 3 prefix gives them a hint that this is a special type of address, one corresponding to a script instead of a public key, but otherwise it works in exactly the same way as a payment to a bitcoin address.


This allows nodes to independently verify whether a given transaction and the bitcoin it is attempting to spend are valid. A UTXO database is used to store change from cryptocurrency transactions. As transactions multiply, the database becomes populated with change records from various transactions. When a transaction is completed and there are outputs that aren’t spent, they are deposited back into a database as inputs that can be used at a later date for a new transaction. Cryptocurrency transactions—such as those used for bitcoins—are similar to cashier checks. You cannot exchange them for custom amounts and must spend the entire amount stored in that data byte. The UTXO of a coinbase transaction has the special condition that it cannot be spent for at least 100 blocks. This temporarily prevents a miner from spending the transaction fees and block reward from a block that may later be determined to be stale after a block chain fork. A single transaction can create multiple outputs, as would be the case when sending to multiple addresses, but each output of a particular transaction can only be used as an input once in the block chain.

  • Real World payment with UTXOsIn the real-world, the UTXOs are almost similar to physical cash/coins.
  • The UTXO model is a design common to many cryptocurrencies, most notably Bitcoin.
  • The larger the database becomes the more expensive it is to run a full node.
  • This is true because, as the name suggests, it is the unspent output of a transaction.

The bitcoin network is designed to propagate transactions and blocks to all nodes in an efficient and resilient manner that is resistant to attacks. To prevent spamming, denial-of-service attacks, or other nuisance attacks against the bitcoin system, every node independently validates every transaction before propagating it further. The rules by which transactions are validated are explained in more detail in Independent Verification of Transactions. Once a transaction has been created, it is signed by the owner of the source funds. If it is properly formed and signed, the signed transaction is now valid and contains all the information needed to execute the transfer of funds. Finally, the valid transaction has to reach the bitcoin network so that it can be propagated until it reaches a miner for inclusion in the pubic ledger . If you want to send a smaller quantity of KMD to a different address, your wallet must send at least one whole UTXO to complete the transaction. Just as you can’t pay for a $5 item by tearing a $10 bill in half and handing one piece to the cashier, you cannot send half of a UTXO to complete a crypto trade. An input is only valid if the ScriptPubKey in its refer- enced output evaluates to true with the input’s ScriptSig. A user’s balance is, therefore, the sum of UTXOs for which the user can supply ScriptSig that would evaluate to true.


JENIKIM is a General Blogger & writer who has been extensively writing in the technology field for a few years. He has written several articles which have provided exciting and knowledgeable information. He is a web content writer, and guest blogger, who offers unique and professional content writing services to online business entrepreneurs.

Recommended Articles

Leave a Reply

Your email address will not be published. Required fields are marked *