<p>The mentioned <code>OP_RETURN</code> output appears to be the footprint of merged-mining <em><a href="https://bitcointalk.org/index.php?topic=5129919.0" rel="nofollow noreferrer">VCash</a></em>, a Mimblewimble-based SHA-256d coin, with Bitcoin. I discovered this via the string <code>0xb9e11b6d</code> appearing in these <a href="https://github.com/vcashorg/vcash/blob/vcash/doc/pool_merge_mining.md#what-do-you-need-to-do" rel="nofollow noreferrer">mining instructions</a>.</p>

CC BY-SA 4.0
2022-04-29T21:16:52.170Z
Many thanks! Helped me to complete my blog post on Merge mining https://zeroknowledgedefi.com/2022/04/29/merge-mining-and-auxiliary-proof-of-work#merge_sec6
George Lowther
CC BY-SA 4.0
2022-04-29T18:25:44.857Z
2022-04-29T19:48:12.820Z
2022-04-29T19:48:12.820Z
Murch
<p>While investigating some Bitcoin coinbase transactions, I notice that a lot of them have an output of the form</p>
<p><code>OP_RETURN OP_PUSHBYTES_36 b9e11b6d…</code></p>
<p>where ‘…’ is 32 bytes, probably a hash of something. I know coinbase outputs can be used for whatever the miner likes, so could be arbitrary. However, I do see a lot of examples starting with the exact same b9e11b6d four bytes. Merge mining is one possibility, but with some googling, I could not find examples using this format.</p>
<p>For example, I started by looking at block <a href="https://blockstream.info/tx/2a85992897c54db7baa8b474bdc03ce7867bd9d8f4b00329cedd223d9997b100?expand" rel="nofollow noreferrer">733528</a>. It has 3 op-return outputs. The first is for merge mining with RSK, the third is the Merkle root of the signature data (indicated by the 4 bytes aa21a9ed), and the second is the mystery one I am asking about.</p>
<p>The previous block <a href="https://blockstream.info/tx/9efb1979d187f25cca5baf7b264704382d057ce5b29514651b6248a43f47aad8?expand" rel="nofollow noreferrer">733527</a> also has this mystery output as its fourth op-return. The block before that does not have such an output, but the one before that does.</p>
<p>Even going back a few years to block <a href="https://blockstream.info/tx/9dc5b4ac6fe3d05cd4a76c472a529c8780c2d188f39b276328e403f105491724?expand" rel="nofollow noreferrer">580000</a> (created 9 June 2019), I see outputs of this form.</p>
<p>Can someone identify what this is? Is it merge mining some other blockchain, or is there another purpose to these outputs?</p>

<coinbase-transaction><op-return><merged-mining>
What is OP_RETURN b9e11b6d?
George Lowther
# What is OP_RETURN b9e11b6d?

(Asked by: username_0 on 2022-04-29)

While investigating some Bitcoin coinbase transactions, I notice that a lot of them have an output of the form

`OP_RETURN OP_PUSHBYTES_36 b9e11b6d…`

where ‘…’ is 32 bytes, probably a hash of something. I know coinbase outputs can be used for whatever the miner likes, so could be arbitrary. However, I do see a lot of examples starting with the exact same b9e11b6d four bytes. Merge mining is one possibility, but with some googling, I could not find examples using this format.

For example, I started by looking at block [733528](https://blockstream.info/tx/2a85992897c54db7baa8b474bdc03ce7867bd9d8f4b00329cedd223d9997b100?expand). It has 3 op-return outputs. The first is for merge mining with RSK, the third is the Merkle root of the signature data (indicated by the 4 bytes aa21a9ed), and the second is the mystery one I am asking about.

The previous block [733527](https://blockstream.info/tx/9efb1979d187f25cca5baf7b264704382d057ce5b29514651b6248a43f47aad8?expand) also has this mystery output as its fourth op-return. The block before that does not have such an output, but the one before that does.

Even going back a few years to block [580000](https://blockstream.info/tx/9dc5b4ac6fe3d05cd4a76c472a529c8780c2d188f39b276328e403f105491724?expand) (created 9 June 2019), I see outputs of this form.

Can someone identify what this is? Is it merge mining some other blockchain, or is there another purpose to these outputs?

**Tags:** coinbase-transaction, op-return, merged-mining


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## 1 answers

### Answer by username_1 on 2022-04-29. Score: 5 | Accepted answer

The mentioned `OP_RETURN` output appears to be the footprint of merged-mining *[VCash](https://bitcointalk.org/index.php?topic=5129919.0)*, a Mimblewimble-based SHA-256d coin, with Bitcoin. I discovered this via the string `0xb9e11b6d` appearing in these [mining instructions](https://github.com/vcashorg/vcash/blob/vcash/doc/pool_merge_mining.md#what-do-you-need-to-do).

> **Comments:**
> **username_0**: Many thanks! Helped me to complete my blog post on Merge mining https://zeroknowledgedefi.com/2022/04/29/merge-mining-and-auxiliary-proof-of-work#merge_sec6  

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