From 0009349ca09527b9939c6cee3b7781be3a7ab09c Mon Sep 17 00:00:00 2001 From: davidsarah <> Date: Sun, 11 Oct 2009 15:30:38 +0000 Subject: [PATCH] SHA-256d does not help for attacks in footnote 7 [Imported from Trac: page NewCaps/WhatCouldGoWrong, version 34] --- NewCaps/WhatCouldGoWrong.md | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/NewCaps/WhatCouldGoWrong.md b/NewCaps/WhatCouldGoWrong.md index 58784e8..be4f46e 100644 --- a/NewCaps/WhatCouldGoWrong.md +++ b/NewCaps/WhatCouldGoWrong.md @@ -35,4 +35,4 @@ where *k* = bitlength(*K1*), *r* = bitlength(*R*), *s* = bitlength(*S*), *t* = b 6. *roadblock*/*speedbump* attacks could be restricted to holders of a read cap by use of an extra signature, as in the Elk Point 3 design (diagram at for mutable files). -7. 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 . 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. +7. 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 . 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.