[PLUG] Does restricting partial words weaken passwords?

[Dave Turner <novalis@novalis.org>]

We discussed on Saturday whether rejecting parts of dictionary words in
passwords would make less secure passwords.

We assumed that a word fragment had 3 characters.

Chance of password of n characters containing part of a dictionary word:
3 = 42.75%
4 = 67.22%
5 = 81.23%
6 = 89.25%
7 = 93.85%
8 = 96.48%

Now vary the size of a word fragment:
1 = 26
100% of search space

2 = 610
90.24% of search space

3 = 7513
42.75% of search space

4 = 46581
10.19% of search space

5 = 124620
1.05% of search space

Other stuff:
Word count of dictionary: 263,533 words.
Size of normal abridged dictionary: about 1/4th of that.
Size of average vocabulary (sources vary wildly): 30,000


-- 
-[Dave Turner                                 Stalk me:  (215)-545-2859]
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