[BitTorrent] Back to Merkle Hash Trees...

Joseph Ashwood ashwood at msn.com
Sun Feb 6 16:53:54 EST 2005


----- Original Message ----- 
From: "Justin Cormack" <justin at street-vision.com>
Subject: Re: [BitTorrent] Back to Merkle Hash Trees...


> sha1 is block based and you cant hash less than a block of
> 64 bytes at a time. So there is an alignment issue.

Actually there isn't. SHA-1 is bit-based, and aligns those bits into 512-bit 
blocks. But in order to prevent certain attacks it also includes a required 
termination that occupies at minimum 65 bits, at maximum 512-bits. If you 
maintain the 512-bit alignment SHA-1 will actually be at it's slowest, if 
you align the last block at 447 bits SHA-1 will be at it's fastest.
                Joe 



 
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