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An Analysis of the Impact of Arbitrary Blockchain Content on Bitcoin [pdf] (ifca.ai)
141 points by nvarsj on March 19, 2018 | hide | past | favorite | 153 comments

So the obvious bit here is that an adversarial actor can poison the blockchain with bits that make downloading, storing and processing the blockchain a highly illegal act.

This may have a chilling effect on participating in the network, thus reducing the number of nodes, and undermining the trust on the blockchain and in the coin because the reduced requirement of computing power needed to mutate the blockchain.

Accordingly a determined actor with enough resources (e.g. a nation-state) can render the bitcoin value-less and use-less at will....

>an adversarial actor can poison the blockchain with bits that make downloading, storing and processing the blockchain a highly illegal act.

Exactly. I brought up the same scenario recently.[1]

The top 2 replies to my comment was basically, "unless you're looking for illegal data, it's not a problem."

That head-in-the-sand ignorance completely misses the point. It's not about how _you_ specifically ignore illegal data and therefore, you have absolution of guilt. It's about the whole world's response to bad data in the blockchain.

[1] https://news.ycombinator.com/item?id=14434786

In addition to illegal content, one could just put a huge amount of data in there to accelerate what seems to be a built in problem of ever increasing storage requirements.

The size of each block is fixed, and the transaction fee is proportional to the number of bytes in the transaction, so you could block people from making transactions (if you were willing to outbid them) but couldn't make the chain grow faster.

hence you can only do that if you have enough money. and that is exactly what visa is doing.

What visa is doing? Can you elaborate?

>> one could just put a huge amount of data in there

That, ah, isn't how that works. You can't just dump terabytes into the blockchain for BTC, LTC, or really any blockchain I can think of that has any sort of adoption.

Always wondered how IPFS deals with this

IPFS isn't a blockchain, and you only receive data you request - it's pull instead of push oriented. So I don't believe it has any problem with this.

IPFS is not an automatically distributed file store. Just like torrents if someone wants to host a petabyte they can. That does not mean anyone else will be mirroring it.

+1 to Setra's comment. Regarding illegal content, IPFS gateways have a blacklist https://github.com/ipfs/infrastructure/blob/master/ipfs/gate...

There's a 1MB cap on block size and it's already being met.

The data embedded in the blockchain can only be extracted using custom tools.

Custom tools can be used to extract any data from almost any other kind of other data, using steganography. You can extract illegal data from innocuous looking tweets, using the right tools.

If the extraction tools do not exceed the cryptographic complexity of a OTP cipher, I doubt that any court will accept that excuse.

It's the difference between taking random bits of your computer to assemble illegal content vs taking one specific set of bits and applying mere transforms to then to retrieve illegal content.

That's a bit of a stretch. There's no reason to obfuscate anything (unless miners are actively and intentionally censoring content) and it'd be straightforward to make a browser.

For example, I don't think it's a defense for the owner of a website to say "this horrible illegal content I'm sharing is only accessible via a custom tool that downloads and decodes image data from me...such as a web browser."

You can make a browser extension extracting illegal data from innocuous images on twitter

You keep saying this as if it isn't beside the point. Creating illegal content by extracting specific digits of pi or rearranging specific pixels of normal images is completely different than taking already-illegal content and uploading it to somewhere it can never be deleted without compromising a lot of other stuff.

Your arguments seem to be of the nature of "information is information; you can't suppress it and you can't make it illegal" but that's not really what this discussion is about.

Only by using your own stock of illegal data.

You don't seem to understand what Steganography is and how it works. Perhaps you should read that article. You cannot produce illegal information out of non-illegal information without having that illegal information somewhere else to use as a key.


the "key" is a very simple algorithm, that is obviously not illegal

But in that case the second image was already stored in (low significance portions) the first. A truly innocuous image won't have such stored data.

That not important.

My point is that you could unknowningly store illegal data, without blockchain being involved.

Anyone sharing the data by torrenting an apparently legal file, reposting an image, or quoting a text could redistribute potentially illegal data.

This problem is not constrained to blockchain.

> My point is that you could unknowningly store illegal data, without blockchain being involved.

The problem with blockchain is that a full node will be knowingly storing and distributing illegal content (or at least is likely to held to be, once the chain is widely known to be infested with such content.) The only way to.stop is to stop storing and interacting with the chain.

With a torrent, you could be unknowingly doing so, but very easily stop doing so with the particular content once you discovered it (without abandoning torrents altogether), which may or not be a complete bar to liability but would probably result in generally more lenient treatment in any situation other than the government is targeting you and the actual offense is pure pretext, in which case the content hardly matters.

There are many non-blockchain scenarios where there is difficult-to-remove data. How would one deal with embedded illegal data stored in firmware? Public records?

And which subsets of illegal data are legal?


If said tweets were reported they would (probably?) be deleted. I'm not sure the "custom tool" defense would really work, you could say the same thing for warez on usenet or even simple jpegs and videos, you need special codecs to view them. Furthermore even plain text embedded in the chain might be enough to get you in trouble in some jurisdiction if it contains hate speech, personal info or harassment material for instance.

The problem with the blockchain is actually its greatest strength: it's immutable. If somebody reports a block containing child porn there's no way to remove it without compromising the blockchain's integrity.

What's meant by "containing"? Regular wallet software doesn't allow access to anything besides transaction data. You won't be able to view any text or images.

The number "Pi" contains all hate speech and other illegal content imaginable.

I'm not a lawyer, I'm not sure what will and won't hold up in court. I think the main problem would be if you operate a node that's not just a consumer but also uploads blocks, it could be argued that you distribute the potentially infringing content. At this point your ability to actually view the content yourself is moot. You're basically operating a peer-to-peer network that can be used to distribute arbitrary data.

>The number "Pi" contains all hate speech and other illegal content imaginable.

That's irrelevant. If you don't think so try downloading child porn, get caught and argue that "it's just decimals of Pi!". Report back with results.

Just to clarify because this is widely misunderstood - hate speech is not a crime in America. Though it is in other western countries like Germany and New Zealand.

Sure, tweets can contain illegal content. That illegal content can be steganographically hidden in innocent images. What makes all this legal for twitter is that as soon as they are aware of illegal content, they delete it. It doesn't matter how well hidden it is, what matters are their actions once they know.

That's the problem with the blockchain: there is no mechanism for deleting data (well, there's pruning, but that's meant to save storage space after processing all the data).

As per my other post here, you don't need anything more than a file to hex converter like http://tomeko.net/online_tools/hex_to_file.php?lang=en and the ability to calculate the gas cost to post on the Ethereum blockchain (second largest coin by market cap and transaction volume).

I thought the same thing about PGP/GPG keyservers. They are supposed to be immutable so if someone uploaded a key containing a jpeg attachment depicting illegal content, the only course of action would be to wipe every server in the network.

Keys aren't immutable. You can remove UIDs you don't like. Even if they were immutable, at least in theory, a keyserver could censor whole keys.

But apparently this is a practical problem. Phil Pennock wrote on oss-security (http://seclists.org/oss-sec/2017/q4/375):

[...] we've had keyservers in Europe shut down because of privacy demands because an append-only mesh-fill datastore can't remove keys and people send out their email address and name paired into a key and then get upset because it's out there; we're one illicit-material-in-photo-uid incident away from global shutdown.

Indeed I was about to write as you have that key servers, or CT logs etc could arbitrarily decide not to include whatever keys they wanted -- although once included, it would be a pain to get rid of them because I think they're built on a Merkle tree structure which is routinely audited: I believe revoking a key doesn't actually delete a key from the database, but rather adds the statement "this key is now revoked", as it's an append-only ledger.

In theory the miners of a public blockchain could also do such auditing, to simply decide to ignore anything containing child pornography, just as they could arbitrarily decide to ignore any transactions. Of course, it's probably expensive to actually check all possible transaction in this way, and they most likely don't have a big enough incentive to. And of course for other sometimes illegal content (e.g. a picture of Mohammed or a particular nation's state secrets) some group of miners would censor while some wouldn't, and it would only take the miners who don't censor to win once for it to forever fork the blockchain.

Keyservers are convenient but they're not critical to PGP's functionality. There are other ways to distribute public keys. Actually in general public key servers are only mildly useful because you can't really trust anything you get from them, you have to use your web of trust of some other way to validate that the key is valid.

On the other hand if you wipe (even partially) Bitcoin's blockchain your basically destroy the currency.

Especially if you consider the possibility of someone loading state secrets onto the chain. It wouldn't take a state actor to initiate that action, but that state actor could render the chain worthless.

That isn't as much of an issue. Once a secret is out, it is out. Something like child porn would be permanently illegal and permanently stored in the chain. Imagine hiding it there, letting a year or two of transactions build upon it before letting people know it was there. You can't remove it. The blockchain is now technically illegal.

I was just thinking about this a lot this week, actually. The really crazy thing is that, due to the PROTECT Act, a person in Japan could legally upload certain manga that the US would consider CP. So one wouldn't even have to risk jail to poison the blockchain.

I think child porn laws are too one-size-fits-all. It's supposed to be to be a disincentive to abusing children to produce the images for profit. Once it's well and truly public so the profit motive is gone, it should become legal. Or at least at the same status as revenge porn if the subjects are identifiable.

Unfortunately, most people are too puritanical to even dare to think about the topic, let alone opens debate it or soften the law.

Every time one of those images is viewed it's an attack on the person in it, the person who could not, and never can give their consent. Also the normalisation of the behavior in the images enables abusers.

The law is there to protect children, profit doesn't feature in the calculations.

Viewing an image obviously doesn't harm anyone directly. What's the chain of causation between that act and the harm, assuming no payment.

Normalization of behavior is a worry that always comes up with "immoral" information. Violent movies, violent video games, adult porn, strip clubs, prostitution, open homosexuality, etc. You'd need actual evidence to support the claim that it makes things worse not better or neutral.

and the developers of the software what would be the legal standing if they are residents of countries like the USA?

could they be persecuted as facilitators of the ilegal distribution?

This gets close to something else I've been pondering lately - how to deal with immutable data structures in the realm of GDPR.

Recitations in GDPR require systems to be designed with privacy in mind. Immutable structures like the Bitcoin blockchain or Merkle trees in other applications would seem to be fundamentally incompatible with some GDPR privacy requirements.

Let's say Google receives a valid right to be forgotten request for an entry in one of their Certificate Transparency logs? Then what? I don't see how it can be dealt with without destroying the integrity of the log.

Some immutable data structures can cope with missing data. Merkle trees are an example: to validate that a leaf is part of the tree, you don't need any of the other leafs (only their direct or indirect hashes). For the Bitcoin blockchain, it has been designed so that transactions where all outputs have been spent can be pruned, after the spending transactions have been validated. It wouldn't be hard to extend this to prune "illegal" transactions, even after they've been included in valid blocks; the only consequence would be that a node wouldn't be able to validate other transactions spending these "illegal" transactions (so it would have to risk accepting an invalid transaction, or rejecting a valid transaction, in both cases risking being on the wrong side of a fork).

You would still have the history of those transaction(s) before they were pruned though...

Simply encrypt the data and upon “deleting it” instead delete the encryption key. This is similar to concerns about backups.

Sure, crypto-shredding seems like a great approach for some things.

But in many cases the whole reason systems use these structures in the first place is so that there's transparency and public verifiability.

> Recitations in GDPR require systems to be designed with privacy in mind. Immutable structures like the Bitcoin blockchain or Merkle trees in other applications would seem to be fundamentally incompatible with some GDPR privacy requirements.

And against whom would I claim my rights, for example: my right to be forgotten (Article 17: The data subject shall have the right to obtain from the controller the erasure of personal data concerning him or her without undue delay [...])?

In the case of a distributed blockchain, who is the controller as defined by the GDPR?

And even if one could identify a controller (say, in the case of a blockchain under centralized control), there are still exceptions to the rights of data subjects. Privacy is key to the GDPR, but not an absolute.

Every person running a full node would theoretically be a controller in that case. But as you say, you could probably make a "business requirements" case if it's just a certificate. Right to be forgotten does not include the right to demand people forget that you owe them money, for example.

What gets more complex is if you put non-business-related "sensitive" personal data in an immutable system, e.g. if you're building an illegal blacklist of union organisers.

I'm not sure it's that shocking a result that data impacted by GDPR may not be stored in an immutable format, given that the law requires you to mutate it under certain circumstances.

There's probably an interesting computer science problem here in how to create a data structure that retains as many advantages as possible from the immutable data structures, but still allows compliance with the GDPR.

It's an attack on memory, part of the War On General Purpose Computing.

Not too long ago, I checked the number of images that were posted on the Ethereum blockchain and I also posted a test image (https://etherscan.io/tx/0x3ee5575306ddc235b0586984172888b47e...). There were 74 images with headers that appeared as jpg, gif, or png already posted before my test image. It's very easy to post to the Ethereum blockchain: just convert back and forth from file to hex using a site like http://tomeko.net/online_tools/hex_to_file.php?lang=en. You might also have to calculate how much gas will be used. I opened a few images and I saw a couple selfies but the oldest jpeg is a certain infamous image from 1999 that I don't think anybody cares to see. I anticipated the chance of illegal images (though it's not exactly a novel idea so I figured somebody would notice it has happened by now if an illegal image has been on the blockchain for a while), so I haven't opened others.

Does etherscan let you search the "Input Data" of a transaction? I can see somebody building a script to parse the blockchain for image headers and convert the hex to a file now that this 'idea' has hit the mainstream. Going to be interesting to see what happens with this.

I wrote the script to parse the Ethereum blockchain from a local copy myself.



Some interesting graffiti on the bitcoin blockchain: http://www.righto.com/2014/02/ascii-bernanke-wikileaks-photo...

I have always wondered this. What will a country do if someone embeds child pornography or a picture of Mohammed or something in the blockchain? Will it then be illegal to store the blockchain in that country? Is a link to such an image much different to an actual image? It seems hard to ever stop this happening with a public permissionless blockchain, pretty much by design.

I haven't looked for obvious reasons but back in the day people were saying that there was already child porn embedded in bitcoin: https://bitcointalk.org/index.php?topic=671894.0

Which is why child porn is one of the Four Horsemen of the Infocalypse: terrorists, pedophiles, drug dealers, and money launderers.

That we are trying to apply flesh space laws to bits just goes to show how stupid we still are: https://en.wikipedia.org/wiki/Illegal_prime

Until we change the laws we have to meet the needs of digital computers instead of the printing press we will have these ridiculous ways of attacking useful new technology.

I'm reading this charitably as you saying that laws that criminalise distribution regardless of intent or knowledge need to be changed to recognise that with the internet people can effectively commit crimes without knowledge or intent. This is particularly relevant where distribution of material (child porn, terrorist material) is criminalised.

This seems a really difficult area that's almost incompatible with the way we do criminal law, because intent and knowledge are so hard to prove either way. Even where there's plenty of circumstantial evidence of intent it is not going to prove it either way.

You could plan to murder somebody for years, leave an evidence trail and then run them over by complete accident. Should that be premeditated murder or manslaughter? In the eyes of a jury it will almost certainly be premeditated murder. You could black out at the wheel and for a while have no knowledge that you have killed. From the philosophical perspective the lines are blurry: Only the individual can actually know, and given the amount to which people can self-delude themselves, even that isn't guaranteed.

Juries do not make decisions on reasonable doubt, and often default to balance of probabilities. Depending on the jurisdiction, when a unanimous verdict cannot be determined a majority one is accepted.

Let's say I have a HDD I write random data to as a block device. What are the implications for me in twenty years if somebody creates an image file format that can decompress some of the linear subregions of my random HDD data. I haven't the time now to do anything but a very simple analysis of this. Intuitively this depends on the size of the drive and the size of the compressed file. Let's say for arguments sake it can encode a prohibited piece of data in 10kB.

At what point of completely random storage material are you likely to have a forbidden piece of data? Well, each terrabyte contains approximately 1e12 such linear subsequences. And we need 1e3010 such subsequences to match a forbidden sequence. So that's 1e2998 or so TB if there is only one forbidden piece of data. With more I think the birthday paradox kicks in. Now if we can encode the forbidden data in 8 bytes or such then we reach the problem much sooner. I doubt that will happen somehow.

Your comment really shows how far we've slid away from the Mens Rea requirement in law. It used to be that every major crime required an intent component. Where the crime was serious enough we had lesser punishments where there was no intent (e.g. manslaughter vs murder).

In the old days it was unfathomable you could be locked up for something you didn't know was a crime.

> In the old days it was unfathomable you could be locked up for something you didn't know was a crime.

This pretty much has never been true, at least in Germany. "Unwissenheit schützt vor Strafe nicht". Even the Roman Law didn't excuse for lack of knowledge https://de.wikipedia.org/wiki/Ignorantia_legis_non_excusat

There are edge cases where you may escape punishment (Verbotsirrtum) but only if it was unavoidable that you erred. Involuntarily distributing child porn may carry lesser punishment, but it will certainly be investigate unless you can assert a privilege such as common carrier status or inability to control the transmission, as for example Tor nodes could.

> This seems a really difficult area that's almost incompatible with the way we do criminal law, because intent and knowledge are so hard to prove either way. Even where there's plenty of circumstantial evidence of intent it is not going to prove it either way.

Not incompatible at all. Most criminal laws actually have a mens rea requirement.

>I'm reading this charitably as you saying that laws that criminalise distribution regardless of intent or knowledge need to be changed to recognise that with the internet people can effectively commit crimes without knowledge or intent. This is particularly relevant where distribution of material (child porn, terrorist material) is criminalised.

No I am making the very simple case that a number is a number and you can't make a number illegal.

All digital information is numbers and banning any of the 4 horsemen of the infocalypse at mere possession will ensure we retard most useful technologies.

The only time that flesh space laws should apply is when flesh space actions are taken.

An example: terrorist training material is sent on how to build a bomb. Until a bomb is built, or a conspiracy to build a bomb is made, nothing illegal should have happened.

Wouldn't that make cyberbullying and slander even in its most extreme forms legal? In those cases often someone is being harmed (with real, flesh space consequences), despite the material being nothing more then numbers.

Slander and cyberbullying are civil law, not criminal law.

But it's just digital information, as you mentioned. It never enters flesh space as real.

Civil law is again very different to criminal law.

You can obviously have a contract between two people for sending digital information between them.

That this only happens in digital space does not mean the contract can't or shouldn't be enforced.

All writing is just splinters of carbon or drops of ink.

How can an element or a wster-based solution be illegal?

Are you attacking freedom of writing now? I am confused.

This is one thing that most of the free world has gotten mostly right: you can say anything you want in writing without having to fear the government.

It needs some corner cases ironed out, obviously, but for the most part you can write whatever you want and not be arrested for it.

You're confused. There's no reason to debate with you. Goodbye.

Note that we only need one number to capture all possible finite content (i.e., the number is chosen such that all binary strings will appear somewhere in the binary representation of the number). A "normal number" [1] satisfies this property. And it is believed that Pi is a normal number.

[1] https://en.wikipedia.org/wiki/Normal_number

I’ve actually written a book on this topic: π

Can I have 1 cent for every spelling mistake I find in your book? ;)

I have no need to legalize child porn just because you think it's necessary for "computers".

I know it's controversial, but I think simply having any information should never be illegal - be it a manual on building bombs, detailed plans of the white house or yes, child porn. Obviously production of such material should be completely 10000% illegal, but we already have laws that cover this extensively.

But simply having a written text, drawn picture, photograph or a video should never be illegal in itself.

> But simply having a written text, drawn picture, photograph or a video should never be illegal in itself.

Exactly! However, reality is very sad.

A map could potentially get you in prison in India https://archive.fo/nLtJX

> The draft bill says: “No person shall depict, disseminate, publish or distribute any wrong or false topographic information of India including international boundaries through internet platforms or online services in any electronic or physical form.” The maximum penalty for wrongly depicting the map will be a fine of Rs1bn ($15m) and imprisonment for up to seven years.

India has active border disputes with both Pakistan and China. The concern is that if an Indian publisher produces maps which don't show the disputed areas as part of India then that would hurt their legal case in international tribunals and hand a propaganda victory to the other side. Land is the foundation of the state so it's not surprising that some governments react harshly to something their leaders perceive as an existential threat.

I wonder if they had scams around that somewhere/time.

It's probably due to border disputes with China.

Revenge porn. You just have information. The ex-girlfriend shouldn‘t make a drama ouf of that. The photo is only a number!

I see a lot of confusion around this topic - sharing porn images without the person's consent should always remain illegal. But just the fact that you have some images on your hard drive? That shouldn't be a crime in itself.

If you have naked images of your ex-partner, they don't magically become revenge porn until the moment you share them without permission(at which point it's a crime and it's already punishable by existing laws).

I don't see the confusion. The claim upthread was that because "in computers" everything is "a number", nothing should be illegal.

Sharing MP3s? It's just a number.

Sending death threats? Just a number.

Directing relatives to the money drop so they may get their loved one back? Just a number.

Sure, but that's not the argument I am making, so perhaps you are replying to the wrong person. I agree that all information is "just a number" and you can outlaw numbers - but I can totally see why sharing certain information would be illegal(as in - the act of sharing). These two are not mutually exclusive.

Digital depictions of illegal acts in real life should remain legal, and illegal acts in real life should also remain illegal. I think that's the best way to resolve this.

What if one's classmates trade photographs of one getting raped? Maybe you would accept this based on your principles. But do you also demand that everybody else accepts this?

Maybe the act in itself wasn't even illegal. But publication may still be. I can have your consent to record, but not to publish. Should we just accept that the publication was illegal, but once-breached, further publication is legal?

So if I want to air something, I publish it anonymously and can then freely refer to it? A lot of laws would have to be rewritten for this to work. Privacy laws and copyright laws among them.

You already have hundreds of gigabytes of child porn on your computer.

What you lack is a program to decode them consistently (I hope).

You can read digital information in any way you please. An image is fundamentally two numbers that give you the height and width and a bunch of number triplets that give you the color values for the pixels inside. You can always find a transformation from any number to any image given you allow the transformation function to be odd enough.

To put it simply, you sound like this guy: https://www.youtube.com/watch?v=8VB3uQHa14g

When trying to outlaw some numbers in some situations.

Using logic similar to chapter six of https://www.scottaaronson.com/papers/philos.pdf , though, you can still draw a meaningful distinction between a normal JPG decoder, and your proposed JPG decoder that interprets the Declaration of Independence as illegal child porn. Your decoder must inevitably have a much higher information content in it, and is a "reduction doing all the work" in that case. So while you've got a mathematical point (no sarcasm, I understand what you are getting at), even on purely mathematical grounds I can argue a meaningful distinction; legally it'll be even easier.

Interestingly, it's a distinction that happens to more-or-less match our own intuitions about the situation, which is something interesting to ruminate about a bit.

The paper says that the bitcoin blockchain already contains illegal content. In particular copyrighted material and possible child pornography. More precisely:

>an image depicting mild nudity of a young woman. In an online forum this image is claimed to show child pornography, albeit this claim cannot be verified

(I don't know exactly what it would mean to "verify" that an image contains child pornography, since in the US and UK at least some of the relevant laws refer only to what the image "depicts", not to the age of the people used in its manufacture. Either way, the copyrighted content seems enough to establish the illegality of the blockchain in principle.) It seems unlikely that any prosecutions will happen though, because blockchain technology has a lot of mainstream support.

There was a tweet [1] from Vitalik Buterin on this exact topic. He was arguing that „possession“ (as in data on the blockchain) does not impose risks on others. Tweet was removed quickly.

[1] https://steemit.com/ethereum/@titusfrost/ethereum-s-vitalik-...

> This entire Ethereum to me wreaks of New World Order involvement, just look at the members of the Ethereum Alliance.

> Also I would suggest trying EOS which is supposed to wipe out Ethereum and hopefully will. I now fully endorse EOS as an alternative to Ethereum.

> I also wanted to address the slanderous attacks against me stating that I am an "Anti-Semite" which is completely bogus. I criticize Zionists who are at the very top of the New World Order Power structure, just under the Jesuits.

What the fuck did I just read?

Some quality tinfoil-hat journalism.

> New World Order

I've memed this online and to friends. It doesn't help that one Ethereum Foundation member was celebrating on twitter about how esoteric people are in the EF even saying that there are oculist members.

it's people like him that make me wary of the crypto fad

The first one would be horrible. The second one, eeh who cares.

Not much you can do about it anyway.

Just to be clear: I'm not suggesting we should implement blasphemy laws :-)

Certain people.

Their problem then.

If they wield any political power then they can make it other a problem for other people too.

Those are usually not democratic countries anyway.

> What will a country do if someone embeds child pornography or a picture of Mohammed or something in the blockchain?

In the US at least, I'd hope that we probably wouldn't criminalize 1M people for the actions of 1. Hopefully in other countries they wouldn't do that either.

Well it depends. If blockchain stored on disk directly contains knows know illegal content it will be picked up by some scanners used by law enforcement. Just like pirated software it won't be enough on it's own but might be a good leverage in the original case that caused computer hardware seizure.

In piracy, you had the _intent_ of doing something, and that's illegal, regardless of whether or not you had the knowledge it was illegal.

In this case, you have an idea that child porn is illegal, but you had no idea it was coming through your blockchain.

Those are very different cases.

There is a possibility of a technical solution:

- You create a special rule for a block known to contain illegal data.

- The illegal data in the block gets NULLed. The other transactions are left untouched.

- The checksum for the next block is no longer calculated, instead it is hardcoded. This means there is no way of verifying the transactions in that block. Perhaps you add a new signature for the block with the NULLed data to make it harder to tamper with.

Once you start doing this workaround once you will probably have to do it repeatedly.

1. That kind of defeats the point of the blockchain.

2. The problem is a technical one as a result of a blockchain allowing content other than financial transactions to be a part of the record.

Wouldn't that allow a 'denial-of-service' like attack? You keep sending illegal content over and over and the next block is never attained.

Maybe I am misunderstanding the process.

I think it will not be a 'denial-of-service' attack but a 'denial-of-decentralization' attack. You can modify an old block and skip all the signatures calculation if everyone agree to take the last block as valid in spite it has a broken chain of calculations. Somewhat similar to the ETH/ETC hard fork.

But there has to he some kind of centralized group that bless the new block. Also, a new client and miner software must be released. Perhaps a new version every time an illegal item is included, or perhaps the program can check the list automatically in a website. In both case, it will break the decentralization.

Isn't intent generally a big deal in law? If I argued that your innocent MS Word doc was illegal because it decoded to child abuse images under a special encoding scheme I just made up, I'd be laughed out of court, and rightly so. It's technically true, but irrelevant. No crime was committed. Doesn't the same principle apply here?

In the UK (and, I believe, the USA) child pornography is a "strict liability" issue — intent is irrelevant, mere possession is itself illegal. This is how teens get nailed for receiving unasked-for sexts from their under-age-of-consent SO.

As with illegal drugs and, in the UK, unlicensed firearms, this means the prosecution doesn't need to prove intent. (Mandatory — usually harsh — sentence terms are usually part of the package with strict liability offenses.)

There IS a mental element to possession in UK law:

> Section 160(1) creates an offence for a person to have any indecent photograph or pseudo-photograph of a child in his possession. [...] "Possession" involves both a physical and mental element. [...] The mental element is knowledge. A defendant must knowingly have custody and control of the photographs found on the device in question.

Downloading the blockchain, should it contain such images, would constitute "making", but it subject to similar mental requirements:

> The act of making or taking the indecent photograph or pseudo-photograph must be a deliberate and intentional act, done with the knowledge that the image made is, or is likely to be, an indecent photograph or pseudo-photograph of a child.

I suspect that not knowing that the blockchain does contain such images, not having knowledge of which transactions do, and that it requires specialised decoding rather than just being embedded per se/a default/intended usage would be enough to raise a defence.


So if a person sees you are about to have your phone searched by police they can send you child pornography and you will go to jail? It somehow doesn't sound like it would hold up in court. At least I feel like it should not.

We should probably be mentioning which laws (and subsections) we're talking about because:

"The presumption of mens rea is rebutted by express provision in the statute excluding the requirement of mens rea. Where the statute is silent as to the requirement the general presumption remains, however, the courts may look at other offences created under the same Act. If the other offences expressly require mens rea, the courts may well take the view that the omission to refer to such a requirement was deliberate and that Parliament intended to create an offence of strict liability." [0]

E.g. there is a section on mens rea for the Protection of Children Act 1978 here: https://en.wikipedia.org/wiki/Protection_of_Children_Act_197...

[0] http://e-lawresources.co.uk/Strict-liability.php

I don't know enough about UK laws or laws in general, but it should be easy to discredit such law. It only takes one rebel tech savvy teen to send his nude sext to whatever celebrity/politician email/phone he can guess while alarming the police - and the press to stir as much shit as possible.

Actually, pardon me for a minute, I have sci-fi short to write :).

In the UK, the police and prosecutors tend to take a common-sense approach: the "rebel tech savvy teen" would be the one who ended up prosecuted for possession.

(Similarly: possession of an unlicensed gun carries a stiff prison sentence. But if someone chucks a pistol on your lawn and you without delay call the police and ask them to take it away, you're probably safe. Picking it up and taking it inside is another matter, however ...)

The USA is a bit different. District Attorneys being elected means they have an incentive to bring charges against "soft" targets who'll take a plea bargain, i.e. hapless teens and people too poor to afford a decent defense lawyer.

"Unsolicited Photographs" is a specific defence to possession:

> The defence is made out if the defendant proves that the photograph in question was sent to him without any prior request by him or on his behalf and that he did not keep it for an unreasonable time.


But we are talking here about not exactly "possession". Imagine I sent you a funny video, but somehow, I appended it with child pornography image, which your video player will easily skip, unless you are specifically looking via forensic measures.

I think it is technically impossible at least improbable to make such encoding scheme, unless your encoding becomes the content itself.

How do you keep the blockchain uncensorable if you start accounting for child porn, and copyright, and all this other stuff that "needs to be taken down".

And if you do all of those things, why even bother with the blockchain and all of its cons in the first place? All that remains is the completely accountable surveillance of users, and I believe that becoming a bigger surveillance machine than even Facebook ever was wasn't the original vision for the blockchain.

I think that unless the main blockchain projects such as Bitcoin, Ethereum, and so on, don't start implementing anonymity by default soon, in a few years they won't be allowed to do it anymore.

One can hope that the Monero market cap catches up with Bitcoin for this very reason.

When PGP was released in the early 90s, one of the arguments used against it was "child porn". When P2P networks using DHT became viable earlier in this century, one of the arguments used against the networks was "child porn".

The tech still remains and still functions, arguments or not.

The difference is between "the technology" and an "implementation of the technology". Sure, P2P DHT exists. Just like blockchains exist. But a specific blockchain, which is append-only, is trivial to make illegal by embedding illegal content in it, making every user of it technically in possession of illegal material. You can use a DHT w/o breaking the law. You cannot store child porn on your computer without breaking the law.

In some cases a link to a file is enough, which would implicate DHT, but due to the nature of the distribution would not compromise the whole network. Cf. Pirate Bay.

What you say is completely true and I agree.

So who's going to shut a blockchain down? I don't see it happening.

If you are interested in this kind of paper, it was in today's morning paper: https://blog.acolyer.org/2018/03/19/a-quantitive-analysis-of...

Isn’t this more like someone throw a stolen item in your bag without you consenting or knowing?

For the cases where data is encoded as the P2PK address those tx should be safe the prune, although downloading them to verify the block would be necessary.

The solution is simple. You need a cryptocurrency where the primitives are simple and predictable. Basically the same reason we don't use eval() on user input. This might very well mean the end for bitcoin if legal parties pick up on this.


Blockchains primarily enable credible accounting of digital events, e.g., money transfers in cryptocurrencies. However, beyond this original purpose, blockchains also irrevocably record arbitrary data, ranging from short messages to pictures. This does not come without risk for users as each participant has to locally replicate the complete blockchain, particularly including potentially harmful content. We provide the first systematic analysis of the benefits and threats of arbitrary blockchain content. Our analysis shows that certain content, e.g., illegal pornography, can render the mere possession of a blockchain illegal. Based on these insights, we conduct a thorough quantitative and qualitative analysis of unintended content on Bitcoin’s blockchain. Although most data originates from benign extensions to Bitcoin’s protocol, our analysis reveals more than 1600 files on the blockchain, over 99 % of which are texts or images. Among these files there is clearly objectionable content such as links to child pornography, which is distributed to all Bitcoin participants. With our analysis, we thus highlight the importance for future blockchain designs to address the possibility of unintended data insertion and protect blockchain users accordingly.

"illegal pornography, can render the mere possession of a blockchain illegal."

I see this as a very strong legal attack vector on full nodes and cryptocurrencies, probably a way around it, is to only allow meta information on a cryptographic form, even then the owner can publish the view key publicly.

A drastic solution is to just prune or don't even allow metadata.

You don't even need the ability to record metadata on-chain to encode arbitrary data. An agreed-upon method of encoding it into ordinary transactions is enough. Even if BTC-style transactions were just inputs/outputs (they're not), you could still encode information down into the satoshi-place of the inputs or outputs themselves. It's even worse for something like Ethereum: essentially the whole point of that blockchain is to encode abritrary (executable) metadata in the form of the contracts themselves.

You could do that with an ordinary bank account though, and call the cops on your bank. In fact, you could do it with any service provider who logs your activity. Simply invent an encoding scheme and encode something illegal in your actions.

Title is sensationalism. Actual paper title is "A Quantitative Analysis of the Impact of Arbitrary Blockchain Content on Bitcoin" — see also Illegal Numbers [0].

[0]: https://en.wikipedia.org/wiki/Illegal_number

The paper isn't wrong though. There are supposedly numbers that correspond to illegal jpg images in the bitcoin block chain.

> There are supposedly numbers that correspond to illegal jpg images in the bitcoin block chain.

How did they come about? Do you have a source for this?

Thats's precisely what the paper linked in the OP describes?

Thanks, we've reverted the title from the submitted “Illegal content embedded in the blockchain” to that of the paper.

This is obvious, even to the casual observer (who care to think beyond the hype.) If this did not occur to you, and you are into bitcoin/cryptocurrencies, you should get out as you're way above your head. (expecting down votes to the truth.)

This comment breaks two of the site guidelines: the one that asks people not to go on about voting (let alone downvote-bait), and this one: "Please don't post shallow dismissals, especially of other people's work. A good critical comment teaches us something."

Saying that someone's work is obvious except to idiots doesn't teach anybody anything; it's just striking a pose. Please don't do that here; instead, explain. If you don't have time to explain, you can save yourself even more time by not posting.


Well, it depends on the design: the format of each entry might be fixed (think of a specific blockchain for a specific task). Yes, a generalistic blockchain is quite likely unable to avoid this.

But who knows.

the format of each entry might be fixed (think of a specific blockchain for a specific task).

As long as you can distinguish between a 0 and 1, or any two states in general, you can store and represent arbitrary data. This basic premise is what makes digital computers so flexible and powerful, and how things like stenography and crypto work.

I think you mean steganography.

> We thus believe that future blockchain designs must proactively cope with objectionable content.

The MimbleWimble blockchain design [1] on the other hand doesn't leave any room to add freely chosen data, mostly due to the lack of any form of scripts.

[1] http://mimblewimble.cash/

If you can trade and breed Pokemon-esque creature in the blockchain, why not illegal content? It's practically untraceable and you don't have to go to trouble of running something like and onion skin router to obscure your identity.

CryptoKitties craze slows down transactions on Ethereum


god this is reposted so many times, SOO MANY TIMES

public service advisory: read the whole btc wiki, there's a lot of great stuff in there!



Links of note: https://bitcoinmagazine.com/articles/bootstrapping-a-decentr...

I don't see relation between these links and the topic. Could you be more specific?

The fact that transactions are scripts is one of the ways that a miner can embed arbitrary data in the blockchain (eg via https://en.bitcoin.it/wiki/OP_RETURN ), which is what the paper is about.

I don't know why the links for agents are relevant.

So we can't even retort mildly tongue and cheek without being flagged by a salty cryptocurrency preacher these days

I loved your comment, and made a funny in response of my own. Don't assume you're right all the time :)

+1, yup yup I see it!

oh great cryptocurrency zealot, how must we repent for our transgressions against the faith?

Please don't make the site worse by posting like this, regardless of how annoying another comment may be.


Unfortunately... you cannot. Your sins in particular are embedded on one of potentially infinite future blockchains and will be read back to you for the remainder of eternity, in shifts

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