Hashed Passwords Readily Cracked by Code Dictionaries, Rainbow Tables

 
 
By Fahmida Y. Rashid  |  Posted 2011-12-17 Email Print this article Print
 
 
 
 
 
 
 

Enterprises can't just store cryptographic hashes of user passwords and think they are protected, as attackers spend the time and resources to run them against dictionaries.

Cyber-attackers have access to various tools to launch their campaigns, such as scanning Websites and applications for vulnerabilities, crafting malicious emails and launching drive-by-download Web portals. They have a growing body of information and automated password cracking tools to breach systems and networks, Imperva said in a report.

Cyber-attackers have greater access to rainbow tables and dictionaries to aid them in cracking passwords, Imperva researchers wrote in their monthly Hacker Intelligence Initiative report released Dec. 14. Organizations have to beef up their password security practices to prevent attackers from successfully guessing passwords and getting access to the network, Imperva said.

Imperva analyzed a list of nearly 100,000 passwords that were exposed by a data breach at film enthusiast Website FilmRadar.com. The site had stored user passwords using the SHA1 hash function, which is a common method used to secure applications, but it wasn't enough, according to Imperva. The strength of a cryptographic hash is irrelevant because attackers can bypass the protections and guess what the password is, Imperva found.

"Contrary to common belief, cryptographic hash functions in general-whether they are SHA-1 or any other cryptographic function-are not impervious to hackers," Imperva researchers wrote in the report.

Password cracking tools that make use of rainbow tables and dictionaries are readily available, and most of them are free for anyone to download, Imperva said. Some popular cracking tools include MD5 decrypter, Cyberwar Zone, Cain and Able, and John the Ripper, according to the report. Many of the tools also rely on hacker forums as a way to request and get additional tables and dictionaries.

"With enough determination, a hacker can easily find tools and multiple dictionaries for password cracking," Imperva researchers wrote.

Rainbow tables contain hash values that have already been precomputed for a large number of alphanumeric text. Although creating these tables is generally a lengthy process, once created, they can be reused over and over again. If the attacker has a hashed value of a password for a specific service, all that needs to be done is to look up the hash in the table and find the corresponding alphanumeric string. Imperva found a hacker Website that makes a rainbow table with more than 50 billion hashed values available to the public.

Strong passwords-those with multiple character types, such as both lowercase and uppercase letters, numbers and special characters, as well as long ones-make it computationally difficult to look up the hash in the rainbow table. However, researchers have recently shown that harnessing the power of cloud, such as renting out computing resources from Amazon Elastic Compute Cloud (EC2) can reduce the time required.

Dictionaries are similar in that they list common passwords with a precalculated hash value. Dictionary-based attacks are effective because as people are still using simple and common passwords, such as "Hello123" and "abcd123."

Imperva ran some of the publicly available tools against the FilmRadar passwords. The team managed to uncover 77 of the 100 most popular passwords in less than 10 minutes using rainbow tables hosted on an online service, according to the report. The 100 most common passwords on the list accounted for 10 percent of the list. Nearly 5 percent of all passwords were guessed in less than two days using dictionaries. Even though it was a slow process, hackers could figure out passwords using multiple dictionaries, Imperva said.

"When it comes to consumers implementing good passwords, we give up. Instead of consumers, [the] responsibility rests on enterprises to put in place proper password security policies and procedures as a part of a comprehensive data security discipline," Imperva researchers said. IT and security teams should consider passwords as highly valuable data, even if PCI and other regulations don't apply, according to Imperva.

Imperva recommends that enterprises not rely on just cryptographic hashes, but to "salt" the entries to protect against rainbow table attacks. A salt value is a random value that is added to the beginning of the password before it gets encrypted, making it even harder to crack the password. A salt of just three-bit length increases the storage and precomputation time for rainbow tables eightfold, according to Imperva.

Enterprises should use passphrases, longer passwords that are easier to remember. Passphrases result in long passwords, but users don't need to worry about writing them down on to a Post-It. Password security should also be enforced, by comparing the password against the same dictionaries being used by attackers. Microsoft recently banned common passwords on its Hotmail Webmail service.

"Advice to users is to choose strong passwords. The rest is up to the business," Imperva said.

The "Imperva Enterprise Password Worst Practices" report follows an earlier report from 2009 on poor consumer password practices.


 
 
 
 
 
 
 
 
 
 
 

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