In fact, in our case, where we use an IPFS hash in an op_return, we remove the IPFS multihash prefix information to post a “bare” SHA256 hash to look like many other hashes being posted in op_returns, to minimize any ability for a miner to identify our transaction. The more projects that do this the better — a form of herd immunity.

Longer term I’m looking for more responsible ways to publish this hash, for instance have the hash be in the witness script data, so that it can be easily purged from nodes that do not wish to preserve it and prevent block size bloat. However, to do so everyone has to do it the same way, ideally have it look like any other transaction. I’ve not quite seen a solid proposal for best practices here.

— Christopher Allen