[rc5] Suggestion for protocol

Honza Pazdziora adelton at informatics.muni.cz
Wed Jun 25 12:49:22 EDT 1997


> 
> The problem here is that the server needs some way to calculate the 
> checksum.  If you're calculating a checksum twice, then that's a lot 
> of wasted cycles, no matter how you go about doing it.
> 
> There's a simpler way.  When a client receives a block, it's checking 
> 2^28 different keys.  Instead of doing a checksum on all of that, 
> have it do a checksum every 2^18 keys (for example).  There would 
> then be 1024 different checksums.  The client is required to 
> return the low 2 bits of each checksum (2048 bits, or 256 bytes).  
> The server then randomly picks one of these 1024 checksums.  It then 
> calculates the checksum for that block (or delegates the task to 
> another machine).  Any client not doing all the required work is 
> pretty likely to get caught after a handful of blocks.

This was exactly my suggestion. I know that it would mean changes in
the RC5 engine to incorporate the checksumming in, but I think it
would be worth it. It would not only catch the fake clients, but also
unwanted errors in the self-made client based on v1.

------------------------------------------------------------------------
 Honza Pazdziora | adelton at fi.muni.cz | http://www.fi.muni.cz/~adelton/
                   I can take or leave it if I please
		     Thanks for having done your DES.
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