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Author Topic: Illegal content in the blockchain  (Read 21927 times)
bitplane
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July 21, 2011, 11:00:51 PM
 #61

I agree with hashcoin, this is an incredibly useful thought experiment and a brilliant attack on the Bitcoin system itself.

So let's ignore the trolly context and get down to the technical details of the attack: Is it possible to encode a small, encrypted jpeg thumbnail in the block chain without mining the block yourself? If so Bitcoin is vulnerable to your run-of-the-mill troll and this should be addressed.

If it's not possible to do unless you actually mined the block, what's from stopping some serious adversary from encoding encrypted child porn into blocks and then releasing the key later on?

What should we do if this happens?
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July 21, 2011, 11:04:00 PM
 #62

The issue is not just storing it unknowingly; for that, it would seem extremely unlikely one could be prosecuted(but IANAL not legal advice etc).  The problem is if you are told you are storing it, you now know it and must delete it.  But it is completely unreasonable to erase bitcoin history, because it is needed for verification.

In other words, this problem won't arise in other contexts because you either don't know about it, or have deleted it.  But here, even if we are told about it, we can't delete it or the whole network breaks.
 
One solution is txs can be blacklisted as bad: nodes won't store them anymore and just reject all TX spending them.  But this will fork the chain.

It might be worth asking EFF about this.
This would open the door to double-spend attacks though.  Pay someone in bitcoins, whilist including the transaction in an illegally encoded data stream, then when you release the key to said illegal content, the transaction is reversed, and you get your coins back.

I don't see any solution to this problem, yet.
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July 21, 2011, 11:10:13 PM
 #63

If someone printed kiddyporn in a 100 dollars bill and you got paid with it, do you need to burn your money?

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July 21, 2011, 11:32:12 PM
 #64

Person A decides to sell off his old hard drive. Before he sells it, he makes some "random" data by making a disk image the size of the drive full of kiddie porn and then encrypts it with 20 minutes of 'cat /dev/urandom'.

You lost me here. Isn't /dev/urandom a one-way function?

It's a source of pseudorandom numbers which are a function of the state of your machine. Actually, absolutely everything a deterministic computer does is a function of it's state, hence it don't have much sense to say /dev/urandom is a function.

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July 21, 2011, 11:37:15 PM
 #65

Person A decides to sell off his old hard drive. Before he sells it, he makes some "random" data by making a disk image the size of the drive full of kiddie porn and then encrypts it with 20 minutes of 'cat /dev/urandom'.

You lost me here. Isn't /dev/urandom a one-way function?

I recently bought a 500GB hard-drive used. Spent 25 hours overwriting it with /dev/urandom (CPU bound). I then spent 5 hours overwriting with /dev/zero (I/O Bound).

Without the "Key" you can't prove whether something is data or meaningless noise.

I meant using a chunk of output from /dev/urandom of the same size as the yet-to-be-encrypted files as the encryption key. And the point is, even if person B checked, it would look like someone used a DBAN disk on it. And the point of the /dev/urandom output as a key is that it would extremely secure, yet person C would presumably have the key, because Person A planed this with malicious intent.

If someone printed kiddyporn in a 100 dollars bill and you got paid with it, do you need to burn your money?
Note: If you put anything on currency and try to use it, then it is defaced. You should not accept his money, because he invalidated it by printing something on it. I know I ruin your point by saying this.

Person A decides to sell off his old hard drive. Before he sells it, he makes some "random" data by making a disk image the size of the drive full of kiddie porn and then encrypts it with 20 minutes of 'cat /dev/urandom'.

You lost me here. Isn't /dev/urandom a one-way function?

It's a source of pseudorandom numbers which are a function of the state of your machine. Actually, absolutely everything a deterministic computer does is a function of it's state, hence it don't have much sense to say /dev/urandom is a function.


This. And im pretty sure, due to the method it gets the numbers, it is completely random. It does use environmental noise.

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July 22, 2011, 12:37:55 AM
 #66

how do others handle this? you can always generate illegal content where numbers are involved. a bank would also not rearrange transactions just because they represent evil data although that evil data would end up at the recipient of the payments and stay stored at the bank.

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July 22, 2011, 12:43:47 AM
 #67

It's a source of pseudorandom numbers which are a function of the state of your machine. Actually, absolutely everything a deterministic computer does is a function of it's state, hence it don't have much sense to say /dev/urandom is a function.
The output of /dev/urandom is typically non-deterministic. It's a function of the entropy pool's state, but that state itself is non-deterministic.

Entropy sources include the clock skew between the CPU's clock source and the network interface's clock source. This is dependent on microscopic zone temperature variations in the quartz crystals which is believed to be truly random. Another source is the timing of data arriving from the hard disk measured by the CPU instruction cycle counter. This is affected by turbulent boundary shear between the hard drive surface and the air around it. This is also believed to be truly random.

Real-world computers are not deterministic computers.

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July 22, 2011, 01:03:00 AM
 #68

...


If someone printed kiddyporn in a 100 dollars bill and you got paid with it, do you need to burn your money?
Note: If you put anything on currency and try to use it, then it is defaced. You should not accept his money, because he invalidated it by printing something on it. I know I ruin your point by saying this.

...

Isn't a note still valid if the defacement compromises less than a certain percentage of the note? I see all sorts of dirty notes in circulation, coffee stains, tears, and even plain aging in general; just print using a UV lasers (accelerating aging selectively) or putting coffee inside the printer's ink cartridge.

(I dont always get new reply notifications, pls send a pm when you think it has happened)

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July 22, 2011, 01:07:04 AM
 #69

...This is affected by turbulent boundary shear between the hard drive surface and the air around it. This is also believed to be truly random.

...

I thought that part of HDDs were evacuated to reduce friction...

(I dont always get new reply notifications, pls send a pm when you think it has happened)

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July 22, 2011, 01:27:42 AM
 #70

...


If someone printed kiddyporn in a 100 dollars bill and you got paid with it, do you need to burn your money?
Note: If you put anything on currency and try to use it, then it is defaced. You should not accept his money, because he invalidated it by printing something on it. I know I ruin your point by saying this.

...

Isn't a note still valid if the defacement compromises less than a certain percentage of the note? I see all sorts of dirty notes in circulation, coffee stains, tears, and even plain aging in general; just print using a UV lasers (accelerating aging selectively) or putting coffee inside the printer's ink cartridge.
I think the law says something along the line of if it makes it unfit to reissue. Printing CP on it in any manner would do this.

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July 22, 2011, 02:56:11 AM
 #71

...This is affected by turbulent boundary shear between the hard drive surface and the air around it. This is also believed to be truly random.

...

I thought that part of HDDs were evacuated to reduce friction...

No, the heads ride on a cushion of air. It it dust that is removed from the cavity. Dust can cause enough turbulence to cause the heads to crash into the disk surface.

These days, hard-drives auto-park the heads when the power is removed. Hard drives I have taken apart also have dust traps with filters near the edge of the platters.

A little off-topic though.

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July 22, 2011, 03:54:21 AM
 #72

cat /dev/null > thisthread

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July 22, 2011, 04:13:55 AM
 #73

cat /dev/null > thisthread
+1

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July 22, 2011, 05:26:49 AM
 #74

Try that with a test file. It will exit immediately without writing anything.

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July 22, 2011, 05:55:56 AM
 #75

Try that with a test file. It will exit immediately without writing anything.

So close, and yet... so very, very far away.

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July 22, 2011, 03:59:21 PM
 #76

Okay, went and tested it: the '>' command overwrites the file; data or not.

You would use the append command ('>>')to avoid overwriting the file.

I was thinking maybe it was a meta suggestion: exit the thread without writing to it Smiley

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July 22, 2011, 04:02:52 PM
 #77

It's a source of pseudorandom numbers which are a function of the state of your machine. Actually, absolutely everything a deterministic computer does is a function of it's state, hence it don't have much sense to say /dev/urandom is a function.
The output of /dev/urandom is typically non-deterministic. It's a function of the entropy pool's state, but that state itself is non-deterministic.

Entropy sources include the clock skew between the CPU's clock source and the network interface's clock source. This is dependent on microscopic zone temperature variations in the quartz crystals which is believed to be truly random. Another source is the timing of data arriving from the hard disk measured by the CPU instruction cycle counter. This is affected by turbulent boundary shear between the hard drive surface and the air around it. This is also believed to be truly random.

Real-world computers are not deterministic computers.

Right, I'm about to correct my comment.

However, aren't hard disks sealed to partial vacuum?.

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July 22, 2011, 04:04:59 PM
 #78

I was thinking maybe it was a meta suggestion: exit the thread without writing to it Smiley

Actually I believe it was a geeky suggestion to blank this entire thread and nothing of value would be lost.

^_^
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July 22, 2011, 04:16:49 PM
 #79


However, aren't hard disks sealed to partial vacuum?.


I suppose there may exist some hard disks designed to operate in a partial vacuum, but those would not include cheap consumer disks. The top plate is too thin to hold a substantial vacuum. I have seen some disks with vent holes you are not supposed to cover.

Specifically the Western Digital WD1600AAJB. Maximum operating altitude: 10,000 feet (3,050m) (using WD1600AB specifications)

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July 22, 2011, 07:13:37 PM
 #80

Aren't the vents for the circuits and perhaps the motor coils?

(I dont always get new reply notifications, pls send a pm when you think it has happened)

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