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Original author: 
Casey Johnston

Few Internet frustrations are so familiar as the password restriction. After creating a few (dozen) logins for all our Web presences, the use of symbols, mixed cases, and numbers seems less like a security measure and more like a torture device when it comes to remembering a complex password on a little-used site. But at least that variety of characters keeps you safe, right? As it turns out, there is some contrary research that supports both how frustrating these restrictions are and suggests it’s possible that the positive effect of complexity rules on security may not be as great as long length requirements.

Let's preface this with a reminder: the conventional wisdom is that complexity trumps length every time, and this notion is overwhelmingly true. Every security expert will tell you that “Supercalifragilistic” is less secure than “gj7B!!!bhrdc.” Few password creation schemes will render any password uncrackable, but in general, length does less to guard against crackability than complexity.

A password is not immune from cracking simply by virtue of being long—44,991 passwords recovered from a dump of LinkedIn hashes last year were 16 characters or more. The research we describe below refers specifically to the effects of restrictions placed by administrators on password construction on their crackability. By no means does it suggest that a long password is, by default, more secure than a complex one.

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Original author: 
Dan Goodin


Thanks to the XKCD comic, every password cracking word list in the world probably has correcthorsebatterystaple in it already.

Aurich Lawson

In March, readers followed along as Nate Anderson, Ars deputy editor and a self-admitted newbie to password cracking, downloaded a list of more than 16,000 cryptographically hashed passcodes. Within a few hours, he deciphered almost half of them. The moral of the story: if a reporter with zero training in the ancient art of password cracking can achieve such results, imagine what more seasoned attackers can do.

Imagine no more. We asked three cracking experts to attack the same list Anderson targeted and recount the results in all their color and technical detail Iron Chef style. The results, to say the least, were eye opening because they show how quickly even long passwords with letters, numbers, and symbols can be discovered.

The list contained 16,449 passwords converted into hashes using the MD5 cryptographic hash function. Security-conscious websites never store passwords in plaintext. Instead, they work only with these so-called one-way hashes, which are incapable of being mathematically converted back into the letters, numbers, and symbols originally chosen by the user. In the event of a security breach that exposes the password data, an attacker still must painstakingly guess the plaintext for each hash—for instance, they must guess that "5f4dcc3b5aa765d61d8327deb882cf99" and "7c6a180b36896a0a8c02787eeafb0e4c" are the MD5 hashes for "password" and "password1" respectively. (For more details on password hashing, see the earlier Ars feature "Why passwords have never been weaker—and crackers have never been stronger.")

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