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Document password truncation with BCryptPasswordHasher

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dstufft committed Mar 26, 2013
1 parent 207117a commit 33c4abb71a3534deab13564eb3168ed0cbfe1786
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  1. +11 −0 docs/topics/auth/passwords.txt
@@ -100,6 +100,17 @@ To use Bcrypt as your default storage algorithm, do the following:
That's it -- now your Django install will use Bcrypt as the default storage
+.. admonition:: Password truncation with BCryptPasswordHasher
+ The designers of bcrypt truncate all passwords at 72 characters which means
+ that ``bcrypt(password_with_100_chars) == bcrypt(password_with_100_chars[:72])``.
+ ``BCryptPasswordHasher`` does not have any special handling and
+ thus is also subject to this hidden password length limit. The practical
+ ramification of this truncation is pretty marginal as the average user does
+ not have a password greater than 72 characters in length and even being
+ truncated at 72 the compute powered required to brute force bcrypt in any
+ useful amount of time is still astronomical.
.. admonition:: Other bcrypt implementations
There are several other implementations that allow bcrypt to be

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