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From Christopher Schultz <>
Subject Re: support for salted passwords
Date Tue, 04 Feb 2014 17:20:31 GMT

On 2/2/14, 2:51 AM, Nick Williams wrote:
> On Feb 2, 2014, at 1:23 AM, Gabriel E. Sánchez Martínez wrote:
>> I am very new to Tomcat but am already getting my feet wet with a
>> web application.  A requirement for this application is form-based
>> password authentication, and I would like to store passwords in a
>> database using salted SHA-512 digests
> I can't speak to most of this email, but don't do this. SHA-x is a
> *fast* hashing algorithm. It's not designed for passwords. The
> problem with fast hashing algorithms is that they are *very*
> susceptible to rainbow table attacks. Modern password-hacking systems
> with 24 GPUs can calculate billions of MD5 and SHA-x hash attacks per
> second.
> I strongly recommend you use a *slow* hashing algorithm such as
> bcrypt, which is designed specifically for hashing passwords. These
> algorithms use more than just CPU/GPU operations (such as memory).
> Password hacking systems can only calculate thousands of these per
> second instead of millions. It's much better protection in case your
> password database is ever stolen.

While you are completely correct in your assessment (crypto hashes don't
make good password hashes), the fact that Tomcat supports only the
former is a somewhat tacit affirmation that simply using crypto hashing
for passwords is good security.

I've been tossing-around some upgrades in my mind for the realm
implementations that would allow for better pluggability for things like
this. Right now, the only way to implement, say, bcrypt, would be to
write your own Realm. That's silly: all you need to do is implement two
methods: mutatePassword() and verifyMutatedPassword().

That opens the door for all kinds of things like bcrypt/scrypt/etc. with
a trivial pluggable interface.

Since it sounds like there's a bit of appetite for this, I may spend
some more time on this (that is, some at all).


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