Threats to anonmyzing peer-to-peer networks

Stephen Blackheath stephen@blacksapphire.com
Tue, 28 May 2002 09:30:29 +1200


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Ihor,

> Is there a way to foil this kind of attack?

As you pointed out, it's easy to find the retrieval keys for the segments of 
the "unwelcome" file.  To elaborate on what Oskar said, the theory behind 
Freenet and Grapevine is that it is easy to retrieve a file if you have the 
key, but it is difficult to map this to a useful IP address.  If you do map 
it to an IP address, it is very unlikely to be the true source of the file.  
The idea is that while you might be able to establish suspicion, establishing 
proof is almost impossible.  It works similarly for requests.  An outside 
agency will find it difficult to determine what you are requesting (unless 
they install some kind of "spyware" on your machine such as Windows XP).

Or they could just put you in jail without the requirement for proof, as they 
have done in various tin-pot regimes such as Britain (I am referring to laws 
regarding disclosure of cryptography keys) and the United States (DMCA, 
military tribunals, turban-wearing etc...).  As Oskar said, it is more likely 
that they will outlaw these systems altogether.   I have been finding out 
about China recently.  If you send an email to China containing the word 
'freenet', then you are blocked (by email address, not IP address) from 
sending any mail to China for a period of about 24 hours.  I have also seen 
this error (I have blanked out the email address):

    3.ÄúµÄÐżþ±»¾ÜÊÕÁË,Çë²»Òª*¢ËͲ»ÊÜ»¶Ó­µÄÐżþ.
        <___@____.com>: host ***.____.com said: 552 Error: content rejected
        <___@____.com>: host ***.____.com said: This Message is not welcome 
    4.ÄúµÄÐżþÌ«´óÁË£¬±»¶Ô*½¾ÜÊÕÍË»ØÁË¡£
    said: 552 Message size exceeds fixed limit

I am also told that my Grapevine Project website is not visible from China, 
which could be interpreted as a mark of respect.

Will they outlaw these systems in the United States?  They haven't yet, to my 
knowledge, but "copyright circumvention devices" (and more seriously the 
development of them) are banned, and that is only a few pen-strokes away.

I can think of two longer-term solutions to this problem:  steganography and 
radio.

There is another threat to anonymizing peer-to-peer networks:  Internet 
Service Providers may prevent end-to-end communication.  That is, they may 
forbid all incoming connections apart from ones associated with approved 
protocols such as ftp.  All communication would have to go through some 
central point, and the Internet would start to resemble television 
(which, as we know, is an essential component of democracy, 
guaranteeing everyone the right to live in a cardboard box and eat dirt 
regardless of gender, race, nationality, sexual-orientation, political views, 
etc.)  One possible solution to this would be to use steganographic email as 
a transport medium, just like in spy novels.  ("Hi, Mum!  How is the weather 
over there?  It's 22.47 degrees here, and the tide is full at 7:34 AM. Please 
find attached a picture of my cat Xyproneroma7E/+giupuss who is orange, 
brown, and white with purple eyes...")


Steve

On Tue, 28 May 2002 06:11, melc@fashionvictims.com wrote:
> On Fri, 10 May 2002, Stephen Blackheath wrote:
> >    In order for someone running a node to know what the contents of a
> >    file stored on their system is, they have to guess the filename of the
> >    file it belongs to, and then look up the file map and see if that CHK
> >    is in the file map. Even if they know the entire contents of the file
> >    they suspect, this is not sufficient information, due to the CBC mode
> >    initialization vector. Hence plausible deniability.
>
> Hi,
>
> I've been thinking about the design of anonymous/censorship-resistant file
> storage systems (like grapevine) and it seems to me that there is a
> problem with this kind of plausible deniability.
>
> Given a file name or identifier it is possible to find out what blocks the
> file consists of (it must be, otherwise you can't download all the blocks
> of the file).  Also each block is (I assume)  uniquely identified by its
> CHK.  Thus, given the name (or some other identifier) of a forbidden file,
> it is possible to create a list of CHKs that make up that file. Given that
> such a list can be made, the "thought police bureau of censorship" simply
> have to actively discover forbidden files (e.g. using a grapevine search
> engine), determine the CHKs of the blocks that make up those files,
> compile and regularly publish a list of forbidden block CHKs and make it
> illegal to request, host or relay any such blocks.  Once they've done that
> it is simply a question of finding out (e.g., by making grapevine requests
> for forbidden blocks, or through more physical "break down the door"
> techniques) who is requesting, hosting or relaying these blocks and cart
> them off to jail.
>
> Is there a way to foil this kind of attack?
>
> Ihor.
>
>
>
>
>
>
>
> ---
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