12 ms·

An Analysis of the Impact of Arbitrary Blockchain Content on Bitcoin [pdf]

141 points by nvarsj 9y ago

randomerr 9y ago
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 http://www.bbc.com/news/technology-42237162 http://www.bbc.com/news/technology-42237162
arthurcolle 9y ago
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! https://en.bitcoin.it/wiki/Agent https://en.bitcoin.it/wiki/Agent https://en.bitcoin.it/wiki/Script https://en.bitcoin.it/wiki/Script Links of note: https://bitcoinmagazine.com/articles/bootstrapping-a-decentralized-autonomous-corporation-part-i-1379644274/ https://bitcoinmagazine.com/articles/bootstrapping-a-decentr...
- vincnetas 9y ago
  I don't see relation between these links and the topic. Could you be more specific?
  - Arnavion 9y ago
    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 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.
- banachtarski 9y ago
  oh great cryptocurrency zealot, how must we repent for our transgressions against the faith?
  - arthurcolle 9y ago
    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
  - dang 9y ago
    Please don't make the site worse by posting like this, regardless of how annoying another comment may be. https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html
- banachtarski 9y ago
  So we can't even retort mildly tongue and cheek without being flagged by a salty cryptocurrency preacher these days
  - arthurcolle 9y ago
    I loved your comment, and made a funny in response of my own. Don't assume you're right all the time :)
    - banachtarski 9y ago
      +1, yup yup I see it!
jwilk 9y ago
Abstract: 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.
- elmar 9y ago
  "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.
  - CamTin 9y ago
    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.
Moodles 9y ago
Some interesting graffiti on the bitcoin blockchain: http://www.righto.com/2014/02/ascii-bernanke-wikileaks-photographs.html 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.
- bb88 9y ago
  > 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.
  - aiCeivi9 9y ago
    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.
    - bb88 9y ago
      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.
  - Tepix 9y ago
    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.
martindale 9y ago
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 https://en.wikipedia.org/wiki/Illegal_number
- zeth___ 9y ago
  The paper isn't wrong though. There are supposedly numbers that correspond to illegal jpg images in the bitcoin block chain.
  - omginternets 9y ago
    > 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?
    - throwawaylolx 9y ago
      Thats's precisely what the paper linked in the OP describes?
- sctb 9y ago
  Thanks, we've reverted the title from the submitted “Illegal content embedded in the blockchain” to that of the paper.
mtgx 9y ago
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.
- hndamien 9y ago
  One can hope that the Monero market cap catches up with Bitcoin for this very reason.
bsenftner 9y ago
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.)
- pfortuny 9y ago
  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.
  - userbinator 9y ago
    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.
    - evanb 9y ago
      I think you mean steganography.
- dang 9y ago
  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. https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html
rogual 9y ago
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?
- cstross 9y ago
  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.)
  - runeb 9y ago
    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.
    - switch007 9y ago
      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_1978 https://en.wikipedia.org/wiki/Protection_of_Children_Act_197... [0] http://e-lawresources.co.uk/Strict-liability.php http://e-lawresources.co.uk/Strict-liability.php
ddalex 9y ago
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....
- phkahler 9y ago
  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.
  - paulgb 9y ago
    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.
    - gcb0 9y ago
      hence you can only do that if you have enough money. and that is exactly what visa is doing.
      - redblacktree 9y ago
        What visa is doing? Can you elaborate?
  - icelancer 9y ago
    >> 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.
oasisbob 9y ago
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.
- ckastner 9y ago
  > 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.
  - pjc50 9y ago
    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.
- greenleafjacob 9y ago
  Simply encrypt the data and upon “deleting it” instead delete the encryption key. This is similar to concerns about backups.
def- 9y ago
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-the-impact-of-arbitrary-blockchain-content-on-bitcoin/ https://blog.acolyer.org/2018/03/19/a-quantitive-analysis-of...
zone411 9y ago
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/0x3ee5575306ddc235b0586984172888b47e92789d672d1aa917f261395efb2495 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 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.
- wakkaflokka 9y ago
  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.
  - zone411 9y ago
    I wrote the script to parse the Ethereum blockchain from a local copy myself.
- nosuchthing 9y ago
  Goatse?
  - zone411 9y ago
    Yes.
Proven 9y ago
Haha what a bunch of clowns... Which part of permissionless do they not understand? But what else to expect from idling academics on gov payroll?
tromp 9y ago
> 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/ http://mimblewimble.cash/
hapnin 9y ago
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.
- otherwiseguy 9y ago
  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.
  - hapnin 9y ago
    What you say is completely true and I agree. So who's going to shut a blockchain down? I don't see it happening.
  - posterboy 9y ago
    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.
bryanph_ 9y ago
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.
XR0CSWV3h3kZWg 9y ago
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.
m3kw9 9y ago
Isn’t this more like someone throw a stolen item in your bag without you consenting or knowing?

141 points by nvarsj 9y ago

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 http://www.bbc.com/news/technology-42237162 http://www.bbc.com/news/technology-42237162

arthurcolle 9y ago

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! https://en.bitcoin.it/wiki/Agent https://en.bitcoin.it/wiki/Agent https://en.bitcoin.it/wiki/Script https://en.bitcoin.it/wiki/Script Links of note: https://bitcoinmagazine.com/articles/bootstrapping-a-decentralized-autonomous-corporation-part-i-1379644274/ https://bitcoinmagazine.com/articles/bootstrapping-a-decentr...

vincnetas 9y ago
I don't see relation between these links and the topic. Could you be more specific?
- Arnavion 9y ago
  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 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.
banachtarski 9y ago
oh great cryptocurrency zealot, how must we repent for our transgressions against the faith?
- arthurcolle 9y ago
  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
- dang 9y ago
  Please don't make the site worse by posting like this, regardless of how annoying another comment may be. https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html
banachtarski 9y ago
So we can't even retort mildly tongue and cheek without being flagged by a salty cryptocurrency preacher these days
- arthurcolle 9y ago
  I loved your comment, and made a funny in response of my own. Don't assume you're right all the time :)
  - banachtarski 9y ago
    +1, yup yup I see it!

jwilk 9y ago

Abstract: 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.

elmar 9y ago
"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.
- CamTin 9y ago
  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.

Moodles 9y ago

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

bb88 9y ago
> 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.
- aiCeivi9 9y ago
  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.
  - bb88 9y ago
    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.
- Tepix 9y ago
  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.

martindale 9y ago

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 https://en.wikipedia.org/wiki/Illegal_number

zeth___ 9y ago
The paper isn't wrong though. There are supposedly numbers that correspond to illegal jpg images in the bitcoin block chain.
- omginternets 9y ago
  > 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?
  - throwawaylolx 9y ago
    Thats's precisely what the paper linked in the OP describes?
sctb 9y ago
Thanks, we've reverted the title from the submitted “Illegal content embedded in the blockchain” to that of the paper.

mtgx 9y ago

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.

hndamien 9y ago
One can hope that the Monero market cap catches up with Bitcoin for this very reason.

bsenftner 9y ago

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.)

pfortuny 9y ago
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.
- userbinator 9y ago
  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.
  - evanb 9y ago
    I think you mean steganography.
dang 9y ago
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. https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html

rogual 9y ago

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?

cstross 9y ago
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.)
- runeb 9y ago
  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.
  - switch007 9y ago
    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_1978 https://en.wikipedia.org/wiki/Protection_of_Children_Act_197... [0] http://e-lawresources.co.uk/Strict-liability.php http://e-lawresources.co.uk/Strict-liability.php

ddalex 9y ago

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....

phkahler 9y ago
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.
- paulgb 9y ago
  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.
  - gcb0 9y ago
    hence you can only do that if you have enough money. and that is exactly what visa is doing.
    - redblacktree 9y ago
      What visa is doing? Can you elaborate?
- icelancer 9y ago
  >> 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.

oasisbob 9y ago

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.

ckastner 9y ago
> 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.
- pjc50 9y ago
  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.
greenleafjacob 9y ago
Simply encrypt the data and upon “deleting it” instead delete the encryption key. This is similar to concerns about backups.

def- 9y ago

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-the-impact-of-arbitrary-blockchain-content-on-bitcoin/ https://blog.acolyer.org/2018/03/19/a-quantitive-analysis-of...

zone411 9y ago

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/0x3ee5575306ddc235b0586984172888b47e92789d672d1aa917f261395efb2495 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 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.

wakkaflokka 9y ago
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.
- zone411 9y ago
  I wrote the script to parse the Ethereum blockchain from a local copy myself.
nosuchthing 9y ago
Goatse?
- zone411 9y ago
  Yes.

Proven 9y ago

Haha what a bunch of clowns... Which part of permissionless do they not understand? But what else to expect from idling academics on gov payroll?

tromp 9y ago

> 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/ http://mimblewimble.cash/

hapnin 9y ago

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.

otherwiseguy 9y ago
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.
- hapnin 9y ago
  What you say is completely true and I agree. So who's going to shut a blockchain down? I don't see it happening.
- posterboy 9y ago
  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.

bryanph_ 9y ago

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.

XR0CSWV3h3kZWg 9y ago

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.

m3kw9 9y ago

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