phc-discussions - Re: [PHC] (not) protecting password length from side-channels (Re: [PHC] Argon2 modulo division)

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Message-ID: <CA+hr98Fhrq=Q1ixh6=MQE5YZRub4UyuHjN9-cUeC9szpV9p2zw@mail.gmail.com>
Date: Fri, 24 Apr 2015 10:09:25 +0200
From: Krisztián Pintér <pinterkr@...il.com>
To: "discussions@...sword-hashing.net" <discussions@...sword-hashing.net>
Subject: Re: [PHC] (not) protecting password length from side-channels (Re:
 [PHC] Argon2 modulo division)

On Fri, Apr 24, 2015 at 12:57 AM, Ben Harris <ben@...rr.is> wrote:
>>> I'm with Thomas on this.  It is futile for PHC candidates to fully
>>> protect the password length.
>
> Isn't the best solution to just hash the password at the source so it is the
> same length

hashing the password reveals the length the same way. you can minimize
the hops the password goes through in plain doing so. but at what
cost? the source is usually some input box on a window or a web page.
we certainly don't want such generic controls to pick and standardize
a hash for you.

also, hashing is not necessary. padding to 128 bytes would be quite enough.