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Security UPDATE--Mathematical Strength of Passphrases--November 3, 2004

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Debunking the Top 5 Myths of Outsourcing Email Security

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1. In Focus: Mathematical Strength of Passphrases

2. Security News and Features

- Recent Security Vulnerabilities

- News: New Security Risk Management Guide

- Feature: Event Response

3. Security Matters Blog

- Microsoft's Virtual Lab

- Need Hands-on Time in a Cisco Lab?

4. Instant Poll

5. Security Toolkit


- Security Forum Featured Thread

6. New and Improved

- SSL VPN for Multiplatform Clients


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==== 1. In Focus: Mathematical Strength of Passphrases ====

by Mark Joseph Edwards, News Editor, mark at ntsecurity / net

Last week, I wrote about why passphrases might be a better idea than passwords. In essence, passphrases are longer and stronger, easier to remember, and more resistant to the assaults of many of the more popular password crackers.

In previous editions of this newsletter, I've mentioned articles by Jesper Johansson, Microsoft security program manager. Recently, Johansson published part 2 of the three-part series "The Great Debates: Pass Phrases vs. Passwords," which compares passphrases and passwords. In part 1 (at the first URL below), Johansson covers the fundamentals, including how passwords are stored. In part 2 (at the second URL below), he looks at the strength of each approach, and in part 3, due out later this month, if I understand correctly, he will offer guidance on how to select stronger passwords and configure password policy.

Part 2 of the series is very interesting because Johansson offers insight into why "longer is stronger" in many cases. Some password-cracking tools attempt to precompute all possible hashes and store them on disk in order to quicken computation time when trying to crack a given password. Johannson points out that precomputing for LAN Manager (LM) hashes is feasible because storing all possible hashes for a 14-character password, for example, based on a 76-character set (the number of characters on a standard American English keyboard when you include lower- and uppercase letters, numbers, punctuation, and special characters) would require about 310TB of storage. Granted, that's a huge amount of data, but storing it is feasible given the file systems available today. On the other hand, trying to store all the possible NT hashes given the same 14-character password and 76-character set wouldn't be feasible because NT's hash algorithm produces longer hashes that would require 5,652,897,009 exabytes (EB) of storage, which according to Johannson, "exceeds the capacity of any file system today." So you can see that using at least 14 characters for passwords and NT hashes makes cracking take much longer than using shorter passwords and LM hashes because all the possible NT hashes can't be precomputed and stored to disk to save processing time.

If all the characters in a password are alphanumeric, and especially if all the letters are the same case, then cracking doesn't take as long as if some nonalphanumeric characters and mixed-case letters are used. As you might know, cracking programs check first for common words using techniques such as dictionary attacks. And if you use only upper- or lowercase letters, the alphanumeric characters add up to only 26 letters and 10 digits, or 36 characters. But if you use the entire set of 76 characters, you greatly increase password strength because you increase the amount of time required to crack your passwords.

Essentially, the strength of a password (or passphrase) is a function of the size of the character set, the number and randomness of characters used from that set, and the computing power of the platform used to attempt to break the password. Because you can't precisely determine which platform crackers might have at their disposal, you could assume the worst-case scenario--that they have the power of a distributed computing network and massive amounts of storage and will therefore be able to crack your password much more quickly than if they worked alone or with a few associates. That means you should consider using password policies that defend against such threats as much as possible by requiring passwords longer than 14 characters, requiring some nonalphanumeric characters, defending your network at all levels against sniffing, and so on.

If you're interested in more information about password strength or need some logical reasoning to justify new password policies for your network, be sure to read Johannson's articles. He goes into a lot of detail (which isn't over the head of a typical network administrator) and offers several anecdotes and cases studies that I think you'll find interesting. Also, please take a moment to visit our Security Hot Topic Web page and answer our latest Instant Poll question: "What password length do you enforce on your network?" I'm interested to know whether you agree that longer passwords are stronger passwords.

On another note, we're happy to announce the IT Prolympics--a contest designed to recognize the most proficient Active Directory (AD) experts in the nation. The gold medal winner will get an all-expenses-paid trip to TechEd 2005. Plus, we'll feature photos and test scores of gold, silver, and bronze winners in the January issue of Windows IT Pro magazine. Learn more about IT Prolympics and enter here:


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==== 2. Security News and Features ====

Recent Security Vulnerabilities

If you subscribe to this newsletter, you also receive Security Alerts, which inform you about recently discovered security vulnerabilities. You can also find information about these discoveries at

News: New Security Risk Management Guide

Microsoft has published a new Security Risk Management Guide that helps people "plan, build, and maintain a successful security risk management program." The new guide is available for free on the company's TechNet Web site.

Feature: Event Response

Windows event logs are a crucial source of information for Windows IT pros. They can warn you of impending problems and alert you to security incidents--but only if you keep on top of them so that you can react to problems quickly. Unfortunately, that's easier said than done. Randy Franklin Smith reviews three tools that monitor event logs and send you alerts.


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==== 3. Security Matters Blog ====

by Mark Joseph Edwards,

Check out these recent entries in the Security Matters blog:

Microsoft's Virtual Lab

Did you know that Microsoft has a virtual lab? I recently learned about the TechNet Virtual Lab, which lets people test the company's latest software in a sandbox environment.

Need Hands-on Time in a Cisco Lab?

The folks over at the Web site have announced they are providing a "free fully equipped lab" with Cisco hardware.

==== 4. Instant Poll ====

Results of Previous Poll:

Do you use Mac OS X on your network?

The voting has closed in this Windows IT Pro Security Hot Topic nonscientific Instant Poll. Here are the results from the 46 votes.

- 33% Yes

- 7% No, but we intend to

- 61% No

- 0% I'm not sure

(Deviations from 100 percent are due to rounding.)

New Instant Poll:

What password length do you enforce on your network?

Go to the Security Hot Topic and submit your vote for

- 14 or fewer characters

- 15 to 24 characters - 25 to 34 characters

- 35 to 44 characters

- 45 or more characters

==== 5. Security Toolkit ====


by John Savill,

Q: Does Microsoft provide a tool to help you determine the meanings of error codes?

Find the answer at

Security Forum Featured Thread

A forum participant has a computer with a file named *yhukyp.exe that runs at boot up. The file is hidden in the All Users startup directory. When he deletes the file, it's copied back from somewhere else. He's looked in the registry under Run and RunOnce and at the system.ini and win.ini files. He wonders whether anyone knows of a guide that might describe where to find the program on the system. Join the discussion at


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Editor's note: Share Your Security Discoveries and Get $100

Share your security-related discoveries, comments, or problems and solutions in the Security Administrator print newsletter's Reader to Reader column. Email your contributions (500 words or less) to [email protected]. If we print your submission, you'll get $100. We edit submissions for style, grammar, and length.


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