[tahoe-lafs-trac-stream] [tahoe-lafs] #1813: Choice of tree-hash
tahoe-lafs
trac at tahoe-lafs.org
Sat Sep 22 10:41:41 UTC 2012
#1813: Choice of tree-hash
------------------------------+------------------------
Reporter: CodesInChaos | Owner: davidsarah
Type: enhancement | Status: new
Priority: minor | Milestone: undecided
Component: unknown | Version: n/a
Resolution: | Keywords: newcaps
Launchpad Bug: |
------------------------------+------------------------
Comment (by CodesInChaos):
The CPU overhead of tree-hashing depends a lot on the particular hash
function, and how you use it. In particular the interaction of the
blocksize, hashsize, padding and finalization. But I estimate that
it's only about 15% compared to a flat hash, for a leaf size of 1 KiB.
So the increase in software complexity using a higher branching factor
doesn't seem worthwhile. If those 15% worry you, I'd rather double the
leaf size.
The official Skein treehash skips finalization for anything but the
root, since finalization is only required for full pseudo-randomness,
and not for pre-image/collision resistance. This halves the overhead
from 15% to 8%.
--
Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/1813#comment:2>
tahoe-lafs <https://tahoe-lafs.org>
secure decentralized storage
More information about the tahoe-lafs-trac-stream
mailing list