The Flaw that May Bring Down Bitcoin or Change it Forever • Hacker News Board

Re: The Flaw that May Bring Down Bitcoin or Change it Forever

#31

Post by Groxx » Wed, May 01, 2013, 5:28 AM UTC

daveasdf wrote: post #5

frisco wrote: post #2

There's already a proposal floating around on the dev list to introduce a new address type, P2SH^2, which would allow the relevant data fields currently being used to stuff the info discussed in the article to become hashes. This would have the effect that if you wanted to stuff arbitrary data, you'd be limited to finding hash collisions. See the thread here: http://sourceforge.net/mailarchive/message.php?msg_id=3070…

While such a scheme might solve this particular method of storing data, it won't make the general problem go away. For instance, if I want to publish an 'n' byte message, I could generate 'n' wallets, each having as their final byte of their fingerprint the n'th byte of my message. Constructing 'n' such wallets will require on average "256*n/2" units of work---quite small, all things considered. I can then transfer a…

Minus transaction fees, yes.

Re: The Flaw that May Bring Down Bitcoin or Change it Forever

#32

Post by rockyleal » Wed, May 01, 2013, 5:34 AM UTC

hobs wrote: post #21

aneth4 wrote: post #13

Earlier quoted context omitted.

This is wrong on all points. A dollar bill is seen by an infitesimally small number of users as opposed to 100% of full bitcoin nodes. Dollar bills are also transient and easy to destroy, whereas the blockchain is permanent and forever. Finally, there is no entity that could determine unacceptable content or delete it, and if there were it would carry the standard abuse problems of any censorship program. So while th…

In terms of taking down the link, I think he means on the server it is on, not remove it from the blockchain.

yep thats what i meant. i'm sorry he/she got so upset whith my analogy somehow. sheesh!

Re: The Flaw that May Bring Down Bitcoin or Change it Forever

#33

Post by AnthonyMouse » Wed, May 01, 2013, 5:45 AM UTC

The flaw in all of this is that you're embedding 20 bytes in the blockchain. In order to do that, you have to choose an encoding method. In order to get the embedded data back out, you have to convey the encoding method and which block is encoded with it to the recipient. Which is totally pointless because if you can convey that to the recipient then you might as well just use the same communications method to convey the original message. The only plausible reason not to would be if the law prohibits the message but not the information about how to construct the message from the blockchain (and even that is not guaranteed). Even then all you would accomplish is to cause the government to pass a new law that prohibits you from telling anyone that a prohibited link is encoded in the block in the same way that you're currently prohibited from telling anyone the link itself.

The real problem here is not that child pornographers would actually use bitcoin to distribute links, it's that assholes who want to damage bitcoin would put contraband in the blockchain in order to cause legal trouble for innocent users.

But I think that's a broader problem than just bitcoin. You can encode anything into anything. Take anything anyone else has posted and xor it with something you want to encode. The output will resemble garbage rather than either input. But now you can post the "garbage" and instructions on what to xor it with to allow anyone to recover your encoded message, and the poster of the other message becomes an unwilling participant in your encoding scheme. It clearly makes no sense to punish distributors of the original message just because the encoded message is contraband. Which doesn't mean there won't be laws that will punish it anyway, but that is the fight that needs to be won -- to not allow stupid laws that would punish innocent people.

Re: The Flaw that May Bring Down Bitcoin or Change it Forever

#34

Post by dalke » Wed, May 01, 2013, 6:08 AM UTC

tyre wrote: post #9

This will neither bring bitcoin down or change it forever. Any information contained in those bytes is just that: information. What can you say in 20 bytes that can have permanent, material damage to human beings? A wonderfully sensationalist title, but really nothing to back it up.

"Nothing to back it up"?

You've considered only the single-use nature of the 20 byte attack, without realizing that that can be done over, and over, and over again.

As moxie pointed out elsewhere in these comments, Travis Goodspeed and Dan Kaminksy embedded a eulogy to the Len Sassaman in the blockchain. See http://pastebin.com/raw.php?i=BUB3dygQ .

But no need to read the other comments, since the author wrote "Some folks have exploited that feature/flaw to publish Wikileaks cables." Information about that publication is in the immediately previous article: "That publishing capability was put into use a couple of days ago when someone publish 2.5 MB of Wikileaks cables in the bitcoin blockchain. It cost a bit of money (about $500) to accomplish that, but the information that was published is now going to be public forever."

A search finds someone who wrote "The wikileaks data starts at transaction 5c593b7b71063a01f4128c98e36fb407b00a87454e67b39ad5f8820ebc1b2ad5".

Therefore, I find your claim that there is "nothing to back it up" untenable.

Re: The Flaw that May Bring Down Bitcoin or Change it Forever

#35

Post by siculars » Wed, May 01, 2013, 6:31 AM UTC

Of all the things threatening bitcoin this is by far the least worrisome. What if people start writing links to censored/illegal content on circulating dollar bills? Nothing, that's what.

Re: The Flaw that May Bring Down Bitcoin or Change it Forever

#36

Post by drivebyacct2 » Wed, May 01, 2013, 6:37 AM UTC

Am I wrong in thinking that this is some sort of "freedom of speech" and that it isn't necessarily wholly different than Bitcoin's sense of "hands off, let it be, decentralization, no one can control/stifle/limit/etc"?

Re: The Flaw that May Bring Down Bitcoin or Change it Forever

#37

Post by drivebyacct2 » Wed, May 01, 2013, 6:39 AM UTC

Xcelerate wrote: post #11

gizmo686 wrote: post #8

Earlier quoted context omitted.

Two points. First, crypto is hard. Unless a system is proven to have a certain property, assume the worst case scenario for your system. Second, SHA256, RIPEMD160 are hashes. By definition (of an ideal hashing algorithm), every output can be generated with the same probability, and changing a single bit of the input will have a 50% chance of changing a given output bit.

I am familiar with how hashes work (I've written a Bitcoin address generator myself). To illustrate what I mean: The Bitcoin address is just some chain of hashes (and a checksum) applied to the public key. To prove that the address IS actually output from the hash functions [and not spam], simply provide the public key along with it. Of course, you might say that is way too much data for the blockchain to handle. So…

Yeah, I think there is actually WIP to do something along the lines of what you worked out.

However, I'm not sure what good identifying "suspicious transactions" is going to do. They're not reversible. You can't really make any attempt to "blacklist" them - you'll almost surely lose.

Re: The Flaw that May Bring Down Bitcoin or Change it Forever

#38

Post by dasil003 » Wed, May 01, 2013, 6:50 AM UTC

How is this any different than a government declaring bitcoin illegal for whatever legal reasoning they can come up with?

It's not practical to shut down everyone with a bitcoin database any more than it's practical to raid every server with wikileaks data. If they're going to declare this nuclear war on bitcoin it's not going to be on the basis of some piece of data which by the point it's in the blockchain is out of the bag anyway.

Re: The Flaw that May Bring Down Bitcoin or Change it Forever

#39

Post by new299 » Wed, May 01, 2013, 6:52 AM UTC

AnthonyMouse wrote: post #33

The flaw in all of this is that you're embedding 20 bytes in the blockchain. In order to do that, you have to choose an encoding method. In order to get the embedded data back out, you have to convey the encoding method and which block is encoded with it to the recipient. Which is totally pointless because if you can convey that to the recipient then you might as well just use the same communications method to convey…

The "encoding method" is ASCII text. The data can be extracted by running "strings *.dat" on the block chain on any UNIX system. After that you can grep through the output.

This is not like XORing data, or as some people have said "everything occurs somewhere in the digits of pi". The blockchain in no sense encodes all possible values, or a fraction thereof, the data is trivial to extract.

This is much more like, it's sitting on the webserver, but not indexed by google. It's actually even worse than that because you can still just grep through the blockchain and find what your interested in.

This may or may not be a problem for bitcoin, but I think it is legally problematic at the moment. This may move us toward a world where it's not illegal to store any particular data or even distribute it. The illegal act might be the viewing or "distribution with intent" or the data. I think that would be an interesting development.

Personally as a user of Bitcoin I've deleted the standard qt client, I personally don't want that data on my computer. I now use a blockchainless client (Electrum).

Re: The Flaw that May Bring Down Bitcoin or Change it Forever

#40

Post by new299 » Wed, May 01, 2013, 6:59 AM UTC

sneak wrote: post #27

frisco wrote: post #2

There's already a proposal floating around on the dev list to introduce a new address type, P2SH^2, which would allow the relevant data fields currently being used to stuff the info discussed in the article to become hashes. This would have the effect that if you wanted to stuff arbitrary data, you'd be limited to finding hash collisions. See the thread here: http://sourceforge.net/mailarchive/message.php?msg_id=3070…

Entirely unnecessary. Transaction fees address the crapflooding issue, and the fact that you can embed only a very small amount of arbitrary data in each transaction means that you're unlikely to be able to harm someone else by forcing them to "possess" your various short byte sequences (which will, on disk, of course be interspersed with the rest of the transaction data). This is to say nothing about the fact that e…

This is actually a big issue for bitcoin, I don't think we should avoid it by saying it's the "standard bullshit".

We also not really talking about small amounts of data (at least at the moment) a few megabytes is relatively significant...

I think the fact that it's "unextraordinary" to possess this data is the interesting thing. That may force a legal distinction which in itself pushes us toward a different understanding of "illegal data" and that perhaps the legal system has to give up on that and move towards accessing or "distributing with intent" being the illegal rather than just possession.