WebApp Sec mailing list archives
6 char passwords and protection against brute force
From: John Wilander <john.wilander () owasp org>
Date: Thu, 23 Dec 2010 00:35:13 +0100
Hi WebAppSec! The Gawker hack and cracking of password hashes got me thinking (http://www.duosecurity.com/blog/entry/brief_analysis_of_the_gawker_password_dump). Today several of the premium services on the web such as Amazon and Apple require a minimum of 6 characters in customers' passwords. I'm not sure if they check against wordlists before accepting a new password, but still, 6 characters allow for brute forcing. So how do these service providers protect the passwords? Salted hashes I presume but no matter what hash algorithm or salt length is used – it's still just 6 characters to brute force. Let's say Amazon or Apple gets hacked and all users' password hashes downloaded. We can also assume the malicious hackers get the source code and config files so they know how the password protection works. A couple of scenarios: · Unsalted hashes, MD5 or SHA1. Rainbow tables already available. Toast. · Unsalted hashes, SHA256, SHA512 or the like. Rainbow tables still not feasible for these? Easier to brute force six character passwords? Guess so. · One salt for all passwords, MD5 or SHA1. Quicker to build a custom rainbow table based on the known salt or quicker to brute forcing each password? · One salt for all passwords, SHA256, SHA512 or the like. Probably not a rainbow table since it has to be built after the hack. Brute forcing of the passwords. · One salt per password, stored alongside the passwords in the DB + any decent hash algorithm. Rainbow tables not usable so it's brute forcing time. If I'm not mistaken in the list above, dictionary and brute forcing will be the weapon of choice as long as we're not facing a static salt or plain hashing, huh? That brings us back to the minimum number of characters. Six characters is not a lot, and the length of the salt or size of hashes will not have a noticeable impact on cracking time. So, is adaptive hashing/multiple hashing the only way to protect short passwords? Are we confident in that Amazon, Apple etc are using such techniques? Do they have migration plans? Say SHA1 x 1,000 right now and migration to SHA1 x 10,000 in 2011. If done right such hash strengthening should not have to involve the real password. Just rehash the current hash another 9,000 times. Would love to hear your thoughts and insights on this. ... and Merry Christmas! /John -- John Wilander, https://twitter.com/johnwilander Chapter co-leader OWASP Sweden, http://owaspsweden.blogspot.com Co-organizer Global Summit, http://www.owasp.org/index.php/Summit_2011 Conf Comm, http://www.owasp.org/index.php/Global_Conferences_Committee This list is sponsored by Cenzic -------------------------------------- Let Us Hack You. Before Hackers Do! It's Finally Here - The Cenzic Website HealthCheck. FREE. Request Yours Now! http://www.cenzic.com/2009HClaunch_Securityfocus --------------------------------------
Current thread:
- 6 char passwords and protection against brute force John Wilander (Dec 23)
- Re: 6 char passwords and protection against brute force Serguei A. Mokhov (Dec 23)
- Re: 6 char passwords and protection against brute force Dan Crowley (Dec 23)