[e-lang] Card game based on covert channels

[Constantine Plotnikov]

David Hopwood wrote:

>Constantine Plotnikov wrote:
>  
>
>>Chris Hibbert wrote:
>>
>>    
>>
>>>>I have just remembered that there is a card game that is based on
>>>>covert channels. It is "Contract Bridge". Covert channel is
>>>>established and used in bidding process. There is also a way to
>>>>introduce a noise in the channel to confuse opponents covert channel.
>>>>
>>>>This game might be a good sample to explain what is a covert channel
>>>>in the protocol in security books or articles.
>>>>        
>>>>
>>>That's an interesting idea, but the fact that the bidders are required
>>>to explain their (partners') bids makes it more overt than covert.  I
>>>think it may make a good opening example, but if you try to explain it
>>>in any depth, the analogy will get pretty strained.
>>>      
>>>
>>This is a covert channel because the formal surface meaning of the
>>protocol is making bids. But partners interpreting it as information
>>about state of their hands.
>>    
>>
>
>I disagree that this is a good example; bidding is an overt channel.
>
>As the Wikipedia article correctly says:
>
>    * Information may only be passed by the calls made and later by the cards
>      played, and not by any other means.
>    * The agreed-upon *meaning* [emphasis added] of all information passed
>      must be available to the opponents.
>
>Use of covert channels in Contract Bridge -- that is, communication channels
>other than bids and the playing of cards -- is normally considered to be cheating.
>
>  
>
You are discussing whether a channel is it secret or not. It is other 
property of channel.

 From wikipedia about covert channels 
(http://en.wikipedia.org/wiki/Covert_channel):
# A covert channel could be defined as a communications channel
# that transfers some kind of information using a method originally
# not intended to transfer this kind of information.

This is most clear definition on that page and is quite aligned with 
understanding that I have got from other places.

Bidding system is covert channel by this definition because bids are not 
originally intended to transfer information about state of the hand from 
one person to another. Overt channel would have been an explicit 
protocol for such negotiations.

I consider the following statement from the article as obviously false one.
# Observers are unaware that a covert message is being communicated.

A receiver is an observer that is aware that covert  message is being 
communicated. Also other observers might be also aware.  But it does not 
changes the fact that message is communicated by using means that are 
not originally intended for this purpose.

Constantine