[dsfjdssdfsd] Blum-Blum-Shub ambiguity in 4086 ...

Dan Brown <dbrown@certicom.com> Mon, 17 March 2014 14:43 UTC

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From: Dan Brown <dbrown@certicom.com>
To: "dsfjdssdfsd@ietf.org" <dsfjdssdfsd@ietf.org>
Thread-Topic: Blum-Blum-Shub ambiguity in 4086 ...
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Date: Mon, 17 Mar 2014 14:42:44 +0000
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Subject: [dsfjdssdfsd] Blum-Blum-Shub ambiguity in 4086 ...
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Two issues:

 

1.      If it is unclear to me from the 4086 description of BBS whether the
state s_i is to be updated after each output. I believe that the state
should be updated to improve backtracking resistance.  (Otherwise, it would
be affected by a similar weak backtracking attack to the one DSS RNG, i.e.
current state compromise the latest output can be distinguished from
random.)

2.      Does the secret state include p and q?  If so, then the BBS suffers
from a more severe backtracking attack: recovering the current state allows
recovery of all the previous states, because p and q allows one to compute
square roots.  This would undermine forward security applications.

 

Best regards,

 


Daniel Brown


Research In Motion Limited