On: Password Requirements: Myths and Madness

[gpderetta]

You could salt the LSH with a different per-user salt.

[wizofaus → gpderetta]

True, if you were only concerned about similarity with the same user's passwords.

[gpderetta → wizofaus]

which in this case we are. We don't want to reject a password because it is similar to some other user password.

Mind, I think the feature is misguided, but it is probably possible to implement it safely.