This is a technical question and I don't have the answer. I would like someone to explain why this data is necessary.

If your answer is receipts or smart contracts, then my question is, "Why not put that in side chains?" I see two problems with this data being in the bitcoin block chain: First, it allows malicious data to be inserted. Second, it takes up more block chain space. Here is the cointelegraph article about music:


This question is a copy of my post here:


2 Answers 2


It certainly isn't "necessary" for proper functioning of the Bitcoin currency, it's just something that people noticed they could do. But there isn't any obvious way to stop it, short of a complete overhaul of the Bitcoin protocol. There are lots of ways to insert small pieces of arbitrary data in a Bitcoin transaction (including even the addresses themselves). So I don't know how we would go about "moving data storage out of the block chain" even if we wanted to. We certainly can't do anything about the data that is already there.

The current standard way to achieve this is with the OP_RETURN opcode in a transaction script. I understand the Bitcoin developers actually took steps to make this feature easier to use: not particularly because they wanted to encourage people adding data to the block chain (as you say it takes up space), but because OP_RETURN is less disruptive than some alternative methods (for one thing, it is limited to fairly small payloads).

  • More Information: Where are they inserting the virus definitions, images and so forth? Is it just a hash of those?
    – berrtus
    May 7, 2015 at 16:45
  • @berrtus The data can be anything you want: it can be an image, or the hash of an image, or a recipe for chocolate chip cookies, or whatever. Any arbitrary string of bytes. Usually it is inserted as unused data in a transaction output script, but there are other ways as well. A hash is a small amount of data and will fit in a single transaction. If you have a lot of data (like an image) you will have to split it over many transactions, and pay a fee for each one, so it can get expensive, but is still possible. May 7, 2015 at 20:02

A transaction can only store a very little amount of data, not enough for music or images. What can be stored is the hash of a music/image file, which is of predictable size, and in my opinion does not present an issue.

  • It is very commonly reported that they are storing images, viruses, and music, If it's just the hash that makes no sense at all. I mean a hash does not contain the original data and you could not even recover such data from the hash.
    – berrtus
    May 7, 2015 at 14:02
  • 1
    @berrtus Can you provide links to these very common reports? The 22hertz article, for example, only talks about "encoding of the copyright" into the blockchain, not the song (and it gives no details about what "encoding a copyright" even means). IMO it looks mostly like a publicity stunt. May 7, 2015 at 14:32
  • Not entirely true. The whitepaper is encoded in outputs as hex here May 7, 2015 at 15:53
  • Here is a CoinTelegraph article: cointelegraph.com/news/113806/…
    – berrtus
    May 7, 2015 at 22:33
  • I noticed I have two CoinTelegraph Articles no I don't work for them.
    – berrtus
    May 7, 2015 at 22:38

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