[rc5] Suggestion for protocol

DevilBunny bunbun at reptile.rug.ac.be
Mon Jun 23 23:56:40 EDT 1997

On Sun, 22 Jun 1997, Fedor Kouranov wrote:

> On 06/22/97 Honza Pazdziora <adelton at informatics.muni.cz> said:

> >The block that the client gets from the keymaster would be divided into
> >1024 subblocks. Each would be encrpted and cumulative checksum would be
> >taken. The result would be 1024 bytes (or any other number), one byte per
> >one subblocks. The keymaster would have to choose number between 0 and
> >1023 randomly and compute the subblock and it's checksum. If it is OK, it
> >believes that also the rest of the block has actualy been processed and
> >accepts the block.
> Totally infeasible. This would mean doubling the number of cycles per key
> just for the sake of paranoia. And still it can be easily faked.

Not double, just 1/1000 

collect 1000 blocks. take from each block at random a range of data and 
it's reported checksum and stuff them in a new block of 1000 ranges.

Give this new block to a trusted client and have it recalculated with a 
new plugin (you *are* working on dynamic changeable modules, right?)

that way everybody will loose (at random) 1/1000 of his cpu power. can 
you live with that? I can.

Other (less realistic) way would be: calculate all blocks, store all 
checksum info (oops... this must be the pitfall) and start checking for 
problems once you completed the keyspace and didn't find a solution.

Devilbunny <bunbun at reptile.rug.ac.be>

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