<p>Bitcoin does not have freely defined input fields of the sort that you describe. In Bitcoin, each input must reference a specific UTXO that is spent, and satisfy the locking conditions that were specified when the output was created. There is one exception which is the coinbase field in the transaction that pays out the block reward, however, this transaction type can only appear once per block and is authored by the miner that found a block.</p>
<p>There is however the &quot;<a href="https://developer.bitcoin.org/devguide/transactions.html#null-data" rel="nofollow noreferrer">null data</a>&quot; (<code>OP_RETURN</code>) <em>output</em> type that allows a sender to attach one output with up to 83 bytes of data. Null data outputs for example find use to anchor timestamps and by colored coin-style networks such as the Omni Layer.</p>

CC BY-SA 4.0
2021-09-02T15:03:36.830Z
2021-09-02T15:03:36.830Z
Murch
<p>I've recently learned that some cryptocurrencies allow the users to attach additional input data to their transaction and would like to know if it's true for Bitcoin as well.</p>
<p>For example, Ethereum allows its users to attach &quot;input&quot; data to a transaction and the senders can hide the actual transaction information inside the &quot;input&quot; data in a hexadecimal format. In Ethereum transaction data, there are many cases where a transaction's input amount is 0 but if you look at its input data, it has a hexadecimal string that has the actual transaction amount and the actual output address.</p>
<p>I wonder whether Bitcoin has a similar function. If so, which column in the Bitcoin transaction data should I look at to get the hidden information? Here's the list of columns in the transaction data.</p>
<p><a href="https://i.sstatic.net/uPUSN.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/uPUSN.jpg" alt="enter image description here" /></a><a href="https://i.sstatic.net/Mc5fD.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/Mc5fD.jpg" alt="enter image description here" /></a></p>

<transactions><smartcontracts>
Decoding Bitcoin transaction data
Sarah Grimes
# Decoding Bitcoin transaction data

(Asked by: username_0 on 2021-09-02)

I've recently learned that some cryptocurrencies allow the users to attach additional input data to their transaction and would like to know if it's true for Bitcoin as well.

For example, Ethereum allows its users to attach "input" data to a transaction and the senders can hide the actual transaction information inside the "input" data in a hexadecimal format. In Ethereum transaction data, there are many cases where a transaction's input amount is 0 but if you look at its input data, it has a hexadecimal string that has the actual transaction amount and the actual output address.

I wonder whether Bitcoin has a similar function. If so, which column in the Bitcoin transaction data should I look at to get the hidden information? Here's the list of columns in the transaction data.

[![enter image description here](https://i.sstatic.net/uPUSN.jpg)](https://i.sstatic.net/uPUSN.jpg)[![enter image description here](https://i.sstatic.net/Mc5fD.jpg)](https://i.sstatic.net/Mc5fD.jpg)

**Tags:** transactions, smartcontracts


---

## 1 answers

### Answer by username_1 on 2021-09-02. Score: 1 | Accepted answer

Bitcoin does not have freely defined input fields of the sort that you describe. In Bitcoin, each input must reference a specific UTXO that is spent, and satisfy the locking conditions that were specified when the output was created. There is one exception which is the coinbase field in the transaction that pays out the block reward, however, this transaction type can only appear once per block and is authored by the miner that found a block.

There is however the "[null data](https://developer.bitcoin.org/devguide/transactions.html#null-data)" (`OP_RETURN`) *output* type that allows a sender to attach one output with up to 83 bytes of data. Null data outputs for example find use to anchor timestamps and by colored coin-style networks such as the Omni Layer.


---

