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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.

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    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 Mar 30 at 19:24
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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.

  • 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 Apr 3 at 18:21

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