Changes between Version 1 and Version 2 of NewCaps/Rainhill


Ignore:
Timestamp:
2011-03-05T01:40:09Z (14 years ago)
Author:
davidsarah
Comment:

simplify under assumption s > r

Legend:

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  • NewCaps/Rainhill

    v1 v2  
    11This is about What Could Go Wrong with the "Rainhill 3" immutable file caps: http://jacaranda.org/tahoe/immutable-rainhill-3.svg
     2
    23(http://jacaranda.org/tahoe/immutable-rainhill-3.png if your browser does not correctly handle SVG.)
    34
    … …  
    21221. ''shape-shifter immutable file'': creator creates more than one file matching the immutable file readcap
    2223
    23 2. See the probability table at http://en.wikipedia.org/wiki/Birthday_Attack . The effective hash length is approximately min(''s'',''r'')+''t'' bits.
     242. See the probability table at http://en.wikipedia.org/wiki/Birthday_Attack . The effective hash length is approximately ''r''+''t'' bits.
    2425
    25263. On Merkle-Damgård hashes with an internal state that is the same size as the hash output (like SHA-256), there are better second-preimage attacks than brute force. See http://www.schneier.com/paper-preimages.pdf . The doubled "SHA-256d" construction used by Tahoe does not help here. This is not significant for roadblock/speedbump attacks because the internal state will be much larger than ''t'' bits, but it is significant for the other second-preimage attacks.