Re:New NIST password guidelines: don't require character typ...
by UnoriginalGuy on Wednesday December 14, 2016 @09:45AM
(#13176270)
> The general attack model is what's known as an offline password-guessing attack.
Most of the time these days we're talking about online services or devices where there are practical limitations (or software limitations) imposed on how quickly we can "guess" a password. This is the most important use of passwords, their strength within a hash should be a concern of the proprietor rather than the user.
Specifically using a salt + pepper, and a hashing algorithm that can be made computationally expensive (or use some other finite computing resource like a lot of memory or even GPU power).
> This is why the oft-cited XKCD scheme for generating passwords -- string together individual words like "correcthorsebatterystaple" -- is no longer good advice. The password crackers are on to this trick.
Them being "on to this trick" doesn't defeat it. It is mathematically stronger. The US-English keyboard has 100 common characters on it. A eight year old child knows over 2,600 words. The key to an "XKCD password" is that one letter in a "random" password must be equal to about half a word in an XKCD-style password (e.g. 8 characters = 4 words, 6 characters = 3 words, and so on).
So:
"12345678" (8 chars)
"OneTwoThreeFour" (4 words)
Are equally as secure (still terrible passwords, but the maths works out). That's because, assuming a "bad guy" knows your trick, the search space is much MUCH larger for an XKCD style password than a traditional password.
Schneier is just mistaken, word-based passwords assuming a reasonable length almost always perform better than random characters, and the maths shows that pretty steadily. We ASSUME a bad guy knows what we're doing, that's a given, but again it is still a much harder task for a bad guy even with perfect intelligence.
Most of the time these days we're talking about online services or devices where there are practical limitations (or software limitations) imposed on how quickly we can "guess" a password. This is the most important use of passwords, their strength within a hash should be a concern of the proprietor rather than the user.
Specifically using a salt + pepper, and a hashing algorithm that can be made computationally expensive (or use some other finite computing resource like a lot of memory or even GPU power).
> This is why the oft-cited XKCD scheme for generating passwords -- string together individual words like "correcthorsebatterystaple" -- is no longer good advice. The password crackers are on to this trick.
Them being "on to this trick" doesn't defeat it. It is mathematically stronger. The US-English keyboard has 100 common characters on it. A eight year old child knows over 2,600 words. The key to an "XKCD password" is that one letter in a "random" password must be equal to about half a word in an XKCD-style password (e.g. 8 characters = 4 words, 6 characters = 3 words, and so on).
So:
"12345678" (8 chars)
"OneTwoThreeFour" (4 words)
Are equally as secure (still terrible passwords, but the maths works out). That's because, assuming a "bad guy" knows your trick, the search space is much MUCH larger for an XKCD style password than a traditional password.
Schneier is just mistaken, word-based passwords assuming a reasonable length almost always perform better than random characters, and the maths shows that pretty steadily. We ASSUME a bad guy knows what we're doing, that's a given, but again it is still a much harder task for a bad guy even with perfect intelligence.