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


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. 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 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 (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?


1 Answer 1


The mentioned OP_RETURN output appears to be the footprint of merged-mining VCash, a Mimblewimble-based SHA-256d coin, with Bitcoin. I discovered this via the string 0xb9e11b6d appearing in these mining instructions.


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