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RE: Suggested "safe" password length
From: JohnNicholson () aol com
Date: Fri, 14 Nov 2003 16:27:01 -0500

I think this is correct. 

As I understand it, the password encryption function breaks passwords into 7-character blocks before encrypting them. 
The impact of this is that for an 8-character password you end up with two blocks - one 7 characters and one 1 
character, each encrypted with the same function. Breaking the encryption on the single character is trivial, and then 
you know how to break the encryption on the 7 character remainder.

By inference, no attack should ever need to break more than a 7-character string (because having broken one means you 
have the key to break the others), and having multiple 7-character strings just gives an attacker 2 (or more) chances 
to hit a combination using a brute force attack.

So, I think the best length is 7-characters, using non-dictionary combinations that include special characters.

At least, this is the theory I've been using. If I'm wrong, I hope someone will let me know so I can change paradigms.

John



In a message dated 11/13/2003 11:37:03 PM Eastern Standard Time, "Michael LaSalvia" <mike () genxweb net> writes:

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Hash: SHA1

Many people say 8 or more but I have read some where that multiples
of 7 are the best to use. It may have been in a class or something I
heard that.

- -----Original Message-----
From: Ashish Sharma [mailto:ashishs () iitg ernet in] 
Sent: Thursday, November 13, 2003 3:06 AM
To: security-basics () securityfocus com
Subject: Suggested "safe" password length

Hi,
I wanted to have an idea about what should be the suggested range of
password lengths and if there is any upper bound.
I was told that there is a range upto which your password is
encrypted
and beyond which the characters are futile. I work on a linux
environment
with md5 encryption of passwords enabled.
TIA
Ashish



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