Re: [TLS] RSA-PSS in TLS 1.3

Hanno Böck <> Thu, 03 March 2016 13:49 UTC

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Date: Thu, 3 Mar 2016 14:49:47 +0100
From: Hanno =?UTF-8?B?QsO2Y2s=?= <>
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Subject: Re: [TLS] RSA-PSS in TLS 1.3
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On Thu, 3 Mar 2016 13:35:46 +0000
"Dang, Quynh (Fed)" <> wrote:

> Why don't we use an even more elegant RSA signature called "
> full-domain hash RSA signature" ?

Full Domain Hashing was originally developed by Rogaway and Bellare and
then later dismissed because they found that they could do better. Then
they developed PSS.


So in essence FDH is a predecessor of PSS and the authors of both
schemes came to the conclusion that PSS is the superior scheme.

> As you know, a SHAKE (as a variable output-length hash function)
> naturally produces a hash value which fits any given modulus size.
> Therefore, no paddings are needed which avoids any potential issues
> with the paddings and the signature algorithm would be very simple. 

You could also use SHAKE in PSS to replace MGF1. This is probably
desirable if you intent to use PSS with SHA-3.

PSS doesn't really have any padding in the traditional sense. That is,
all the padding is somehow either hashed or xored with a hashed value.
I don't think any of the padding-related issues apply in any way to
PSS, if you disagree please explain.

(shameless plug: I wrote my thesis about PSS, in case anyone wants to
read it: - it's been a while, don't be too
hard on me if I made mistakes)

Hanno Böck