[viff-devel] [issue80] Broadcast

[Ivan Bjerre Damgård]

Quoting Janus Dam Nielsen <jdn at cs.au.dk>:

> In the simple case I want to shout out a number to everybody, even  
> somebody who is eavesdropping.

But secrecy of what you shout is not the real problem. The problem is  
to make sure everyone agrees on what was said. This is not obvious in  
the case where people may not follow the protocol. For instance, if  
you want a solution that does not depend on computational assumptions,  
then if a third or more of the players are corrupt, then there is NO  
solution.

Think of 3 players A,B and C, where A wants to broadcast a message,  
say 0 or 1. One player may be corrupt. So A is supposed to send a bit  
b to both B and C. Say B hears 0 from A. He doesn't know if A said the  
same to C. He can ask C what he heard, but if C says "A said 1 to me",  
there is no way to tell if A or C is lying..

regards, Ivan


>
> --
> Janus
>
>
> Den 10/03/2009 kl. 12.23 skrev Ivan Bjerre Damgård:
>
>> It can definitely be useful to have a broadcast method, for  
>> instance to complete the implementation of the asynchronous  
>> maliciously secure protocol, we will need broadcast.
>>
>> But one needs to be careful about what kind of security we want.  
>> There is a whole jungle of protocols, depending on whether it is  
>> unconditional or computational security, synchronous or  
>> asynchronous network, and what number of players you assume can be  
>> corrupt. I think a protocol of Bracha has in fact already been  
>> implemented in VIFF
>>
>> regards, Ivan
>>
>> Quoting Janus Dam Nielsen <tracker at viff.dk>:
>>
>>>
>>> New submission from Janus Dam Nielsen <janus.nielsen at alexandra.dk>:
>>>
>>> I would like to see a broadcast method in the Runtime class. The
>>> purpose of the broadcast method should be to distribute a public value
>>> among all parties (or some subset of parties).
>>>
>>> A case: All parties in a computation needs to read a value from
>>> standard in, and it is a different value for each party. We want to
>>> tell the value to everybody else.
>>>
>>> An example use could be like the input method:
>>> a,b,c = runtime.broadcast([1,2,3], value)
>>>
>>> Similarly, broadcast can be used in a conditional if only some subset
>>> of parties wants to distribute a value.
>>>
>>> ----------
>>> assignedto: mg
>>> messages: 310
>>> nosy: jdn, mas, mg
>>> status: chatting
>>> title: Broadcast
>>> type: wish
>>>
>>> ____________________________________
>>> VIFF Issue Tracker <tracker at viff.dk>
>>> <http://tracker.viff.dk/issue80>
>>> ____________________________________
>>> _______________________________________________
>>> viff-devel mailing list (http://viff.dk/)
>>> viff-devel at viff.dk
>>> http://lists.viff.dk/listinfo.cgi/viff-devel-viff.dk
>>>
>>
>> _______________________________________________
>> viff-devel mailing list (http://viff.dk/)
>> viff-devel at viff.dk
>> http://lists.viff.dk/listinfo.cgi/viff-devel-viff.dk
>
> _______________________________________________
> viff-devel mailing list (http://viff.dk/)
> viff-devel at viff.dk
> http://lists.viff.dk/listinfo.cgi/viff-devel-viff.dk
>