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A comment on New NIST password guidelines: don't require character types or rotation. Parent comment

Re:New NIST password guidelines: don't require character typ... by criddell on Wednesday December 14, 2016 @04:41PM (#13179915)
After reading through most of that, it seems that the big problem with the XKCD scheme is that it's often impractical. Too many sites restrict password length and so you are forced to use the Schneier modification to get more entropy per character.

If you make a password from an alphabet of 64 characters (upper and lower case, digits, and some special characters), there are 6 bits per character of entropy so a ten character random password could have 60 bits of entropy.

If you are choosing words from a list 4000 words long, there are 11 bits of entropy per word and so you would need to string together five random words to get a password of equal strength. The big problem then is having enough space to type that many characters.

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Re:New NIST password guidelines: don't require character typ... by PwdRsch on Wednesday December 14, 2016 @04:53PM (#13179997)
Yep, unfortunately for passphrases the maximum acceptable password length on web sites tends to be the #1 factor limiting their use. I created sample passphrases and tried them on a handful of different sites to measure the problem. See starting slide 31 in this presentation (PDF): http://www.passwordresearch.com/files/How%20Secure%20Are%20M...
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Re:New NIST password guidelines: don't require character typ... by criddell on Thursday December 15, 2016 @11:09AM (#13185541)
Do you know why sites would set a low limit? I can understand limiting to, say, a couple hundred characters, but 16 is ridiculous. These days, all anybody is going to store is a salted hash so the passphrase length should be mostly irrelevant.

Edit: that's a pretty nice slide deck. Thanks for the pointer.

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Re:New NIST password guidelines: don't require character typ... by dragonwriter on Thursday December 15, 2016 @11:10AM (#13185566)
> These days, all anybody is going to store is a salted hash so the passphrase length should be mostly irrelevant.

Since I still run into services where the "forgot password" mechanism emails your current password in the clear, this is unfortunately not as true as one would hope.

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