[BitTorrent] BT2 & hash trees

Olaf van der Spek OvdSpek at LIACS.NL
Thu Jul 22 13:42:36 EDT 2004


Gregorio Roper wrote:
> Olaf van der Spek wrote:
>>Gregorio Roper wrote:
>>>Olaf van der Spek wrote:
>>   7
>> 5   6
>>1 2 3 4
>>
>>Transfer order: 3, 1, 2, 4.
>>To verify 3, I need 4 and 5, so I request 2 hashes.
>>To verify 1, I need 2, so I request 1 hash. (You already have 5 from the 
>>previous step).
>>To verify 2, I need 2, which I already have, so I request 0 hashes.
>>To verify 4, I need 4, ".
>>To I transfered just 2 + 1 = 3 hashes, which is n, not 2n.
>>So it doesn't cost more hashes then transfering 1, 2, 3 and 4 up front.
> 
> 
> I was thinking along these lines:
> To verify 3 I need the hashes of 3,4 & 6

You don't need 3, as you calculate it from the data itself.
You need 5, not 6, as you can calculate 6 yourself from 3 and 4 and 
without 5 you can't verify 6.


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