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Re: ADS Password Storage Protection
From: Eoin Miller <eoin.miller () trojanedbinaries com>
Date: Tue, 18 Jul 2006 16:54:57 -0400

Roger A. Grimes wrote:
Length is always more important than complexity because password
keyspace is expressed as Y^X, where Y is the number of possible
characters and X is the password length. Thus, any similar increase in X
has significantly more impact than to Y.
Roger,

That relies upon the assumption of all attackers performing attacks that attempt all possible characters all the time. In most attempts to break passwords, the attacker will remove the uncommonly used characters from being attempted. Since users try and follow the bare minimum requirements, not adding complexity requirements can have a detrimental effect. Consider the following hypothetical situation:

An internal employee has sniffed hashes from a network (we will assume there are no shortcuts/weaknesses in the algorithm). The internal company policy only requires 8 character length passwords and nothing more. Which will be broken first by the attacker who is only trying to crack a hash with lowercase letters [a-z]?

A hash generated from a 10 character password that was created with only lowercase [a-z].

or

A hash generated from a 8 character password that was created with lowercase [a-z], uppercase [A-Z], numerical [0-9].

The likely combinations to guess are not only derived from the length of the password but also from the minimum requirements instituted by the password policy. Having password complexity requirements forces attackers into using more possible combinations. I will not argue that length or complexity is more important than the other because situations can arise that expose the weakness of either. Both are required (and complement each other) when instituting a sound password policy.

--Eoin

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