For the input - the ruble, but there is no way out: how do third-party files get into the blockchain and what to do about it

    Hi, Habr!

    I promised to share philosophical thoughts about the blockchain. Therefore, today there will be an article on a topic that often appears in the press: about “forbidden” files in blocks.

    In March 2018, in one of the blocks of Bitcoin, found links to child pornography and images of a sexual nature. On a regular website, forum or social network, you can remove unwanted materials and find the one who posted them. But it won't work with the blockchain, and that’s why the event has become quite loud.

    Information in the blockchain is impossible to correct. As we know, already created (closed) blocks of the blockchain are unchanged due to cryptographic encryption, where the hash of the previous block is included in the next one. This is the key "trick" of technology, so to speak, feature by design. And that means that you cannot delete images and links that have become part of the block. In addition, the wallets of most cryptocurrencies are anonymous: unlike social network accounts, they are not tied to bank cards and phone numbers. Therefore, to track the one who posted the illegal content is impossible.

    I immediately had many questions: how does adding data to the blockchain "work"? Is it available to ordinary users? And can the authorities impute something to blockchain companies? That's what I managed to find out.

    From theory to embodiment

    The idea that you can “hide” illegal content in the blockchain was not only in the IT community. Back in 2015, Interpol warned that it is technically possible to store malware on the blockchain, which cannot be removed from there. And in 2017, researchers from the Rhine-Westphalian Technical University of Aachen in Germany actually discovered the prohibited content in Bitcoin and investigated it.

    In each transaction of the blockchain, some third-party data may be stored, this is provided for by the block structure. In the study (pp. 2-5), scientists list the methods by which they can be put there. Methods 2-4 are available only to miners, and for 1-2 you need basic knowledge of programming languages.

    • P2SH input scripts (not some types of addresses are used to send bitcoins).
    • OP_RETURN method: embedded in the bitcoin protocol code that allows you to store an increased amount of data.
    • The coinbase data, or unlocking script field in a block: you can specify anything from 2 to 100 bytes in it.
    • Fields of usual transactions for transferring bitcoins - for example, when generating keys and hashes for a given pattern.

    All these methods allow you to embed a small amount of third-party data into the blockchain: a short text or a link. But there are methods that reveal more possibilities. One of them is the use of the built-in scripting language (up to 60 KB of third-party data in each block). Here you have to pay a commission to miners. Another method is Data Oracle. Oracle is an application that connects the blockchain to an external source. With it, you can put third-party data in the blockchain as a series of transactions, and they will also be immutable.

    There are intermediary services that offer the placement of arbitrary data on the blockchain: for example, CryptoGraffiti or Satoshi Uploader.

    According to the researchers, there are about 1600 files in the bitcoin blockchain. About 10 of them contain pornographic content and links to it on the Internet and Darknet.

    What is the law?

    There are no judicial precedents related to illegal files in the blockchain. Therefore, I could only assume the consequences, relying on the laws of different countries.

    Threats to ordinary users

    In Germany, Great Britain, the United States and a number of other countries, the storage of content prohibited by law is also illegal. In many states, it is considered a crime to distribute such content. But is it possible to equate the use of the blockchain to the storage or dissemination of information?

    In normal Bitcoin transactions, the copy of the blockchain is not downloaded to the user's computer. Therefore, ordinary users can not be called "keepers" of illegal files.

    Risks for miners and blockchain in general

    When mining, the registry or its parts are loaded onto the user device. Therefore, there are concerns in the community that illegal content may be a convenient excuse for restricting mining or using the blockchain.

    Head over to the other side. Can images and links of dubious nature uploaded to the blockchain be called illegal content? The difference has already been pointed out by IT experts: the data in the blockchain is cryptographically encrypted. Therefore, in order to upload photos from it, precise instructions are required on the location and method of decrypting this data, and before decryption they are not identified as images at all.

    A professor at Princeton University and Bitcoin researcher Arvind Narayanan comments on references to prohibited materials (which constitute a large part of the “illegal content”). He recalls that from a legal point of view, the link and the original are not at all the same.

    So, the publication of links has consequences rather not for the blockchain, but for sites on which the "original" is located. By the way, most of them are in Darknet. And the placement of images of any content in the blockchain is not open access, but something like computer shorthand. Therefore, according to today's laws, it is unlikely to impose any sanctions on the blockchains. But the public response was strong, and some companies have already announced greater control over users. Thus, the Money Button payment processing application, which is associated with one of the episodes of adding illegal content to the blockchain, reports that it will block users for such actions and notify the authorities.

    Fighting illegal content: methods and tools

    It is really impossible to delete third-party files from an already created block in the blockchain. Theoretically, this can be done with the help of a fork, but de facto no one will perform such a complex operation for the sake of several links or images.

    Bans and “blacklists”, which are claimed services like Money Button - a measure for prevention: the content of the banned user will not disappear. Automatic data pre-moderation can also be circumvented.

    Does this mean that the authorities have a convenient excuse for sanctions against blockchain companies? And will we see legal cases related to pornographic materials in Bitcoin and other ecosystems? So far, one thing is clear: on the basis of existing laws, it is very difficult to make convictions, and blockchain companies have good arguments in their defense.

    The only real threat that exists for the industry is the public outcry. Some companies will really begin to distribute bans and moderate content. But the part will not give up its principles and will not interfere with the work of the ecosystem. I am sure that our project will be among the second.

    PS: Attention, crosspost! We decided to post this article with the team on VC.Ru, according to the new rules. Here:

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