Re: Theoretical limits for password length

From: Gregory G Rose (ggr_at_qualcomm.com)
Date: 08/25/05 

Date: 25 Aug 2005 11:17:07 -0700

In article <dej8q5$2mrm$2@agate.berkeley.edu>,
David Wagner <daw-usenet@taverner.cs.berkeley.edu> wrote:
>Milan VXdgsvt wrote:
>>Let's have a perfect block cipher, with blocks of length N. The cipher
>>has a password of length P. An attacker gets to know K adjacent blocks
>>of plaintext-ciphertext, and has virtually unlimited computing power,
>>enabling a brute search of all passwords.
>>The question is, is there a cipher such that the attacker needs much
>>more than just P/N blocks?
>
>Short answer: No.
>
>Slightly longer answer: Once the entropy in the plaintext exceeds
>the entropy in the password, you're screwed.

ITYM "once the *redundancy* in the plaintext
exceeds the entropy in the password...".

Greg. 

-- 
Greg Rose
232B EC8F 44C6 C853 D68F  E107 E6BF CD2F 1081 A37C
Qualcomm Australia: http://www.qualcomm.com.au

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