<blockquote>
  <p>For example, a blank input could be used to guarantee a particular output was included in a transaction, using SIGHASH_SINGLE | ANYONECANPAY in combination with SIGHASH_NONE.</p>
</blockquote>

<p>You cannot use <code>SIGHASH_SINGLE | ANYONECANPAY</code> in combination with <code>SIGHASH_NONE</code>. You cannot have two or more of <code>SINGLE</code>, <code>ALL</code>, <code>NONE</code> on a single input, they can only be combined with <code>ANYONECANPAY</code>.</p>

<p>Moreover, if you are able to create a zero value (or even dust output), that single output alone will be enough to enforce the rule "If you use this output, you must send X BTC to this address". However, if you have a zero value or dust output, no one is really incentivized to include it - after all, you aren't contributing any significant value to the tx. In fact, you are raising the fee due to the extra input/output size. People will just drop your input and output and build a tx without it.</p>

CC BY-SA 4.0
2019-04-03T18:21:07.583Z
Thanks. I actually meant combining separate inputs with each signature. But I realized this is not possible so it's not worth thinking about
nick carraway
CC BY-SA 4.0
2019-03-30T20:50:56.413Z
2019-03-30T20:50:56.413Z
Raghav Sood
<p>Is it possible to include a blank input in a transaction?</p>

<p>For example, a blank input could be used to guarantee a particular <code>output</code> was included in a transaction, using <code>SIGHASH_SINGLE | ANYONECANPAY</code> in combination with <code>SIGHASH_NONE</code>. </p>

<p>Of course you would still need to include miner fees within another input. </p>

<p>Correct me if I am wrong, but although spending 0-output utxos is legal, it is fairly difficult to generate 0-output utxos, as Bitcoin Core does not support generating these transactions beneath the dust limit.</p>

<p>Likewise, OP_RETURN provides 0-value-output utxos, but they could not be spent as part of a <code>sighash_single</code>, since they are unspendable.</p>

CC BY-SA 4.0
2019-03-30T19:24:34.843Z
I'm not sure what you mean by a "blank" input.  AFAIK, a transaction includes a list of inputs, each of which must specify a transaction ID and index that must refer to an existing and unspent output.
Nate Eldredge
<blockchain><utxo>
Signing a blank input?
nick carraway
# Signing a blank input?

(Asked by: username_0 on 2019-03-30)

Is it possible to include a blank input in a transaction?

For example, a blank input could be used to guarantee a particular `output` was included in a transaction, using `SIGHASH_SINGLE | ANYONECANPAY` in combination with `SIGHASH_NONE`.

Of course you would still need to include miner fees within another input.

Correct me if I am wrong, but although spending 0-output utxos is legal, it is fairly difficult to generate 0-output utxos, as Bitcoin Core does not support generating these transactions beneath the dust limit.

Likewise, OP\_RETURN provides 0-value-output utxos, but they could not be spent as part of a `sighash_single`, since they are unspendable.

**Tags:** blockchain, utxo

> **Comments:**
> **username_1**: I'm not sure what you mean by a "blank" input.  AFAIK, a transaction includes a list of inputs, each of which must specify a transaction ID and index that must refer to an existing and unspent output.  

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## 1 answers

### Answer by username_2 on 2019-03-30. Score: 2 | Accepted answer

> For example, a blank input could be used to guarantee a particular output was included in a transaction, using SIGHASH\_SINGLE | ANYONECANPAY in combination with SIGHASH\_NONE.

You cannot use `SIGHASH_SINGLE | ANYONECANPAY` in combination with `SIGHASH_NONE`. You cannot have two or more of `SINGLE`, `ALL`, `NONE` on a single input, they can only be combined with `ANYONECANPAY`.

Moreover, if you are able to create a zero value (or even dust output), that single output alone will be enough to enforce the rule "If you use this output, you must send X BTC to this address". However, if you have a zero value or dust output, no one is really incentivized to include it - after all, you aren't contributing any significant value to the tx. In fact, you are raising the fee due to the extra input/output size. People will just drop your input and output and build a tx without it.

> **Comments:**
> **username_0**: Thanks. I actually meant combining separate inputs with each signature. But I realized this is not possible so it's not worth thinking about  

---

