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Re: [Cfrg] A new MGF for RSA-PSS based on SHAKE

Jim Schaad <ietf@augustcellars.com> Wed, 26 September 2018 23:39 UTC

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From: Jim Schaad <ietf@augustcellars.com>
To: 'Peter Gutmann' <pgut001@cs.auckland.ac.nz>, cfrg@irtf.org
References: <3B4BE320-418B-4FC1-8427-0EF2F58A0F01@vigilsec.com> <6FD96340-0D8D-44C0-9374-9D7A3F36F967@gmail.com> <27af097a-6769-fcc4-7b28-12c1ea77055a@uni-paderborn.de> <000d01d45041$a8930250$f9b906f0$@augustcellars.com> <a21a5c72-f9e5-2eb7-4144-bdded4c8321d@uni-paderborn.de>, <E7059316-430B-4DE0-A0C7-09A0B6783C0F@ericsson.com> <1537989175802.46714@cs.auckland.ac.nz>
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Date: Wed, 26 Sep 2018 16:38:38 -0700
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Subject: Re: [Cfrg] A new MGF for RSA-PSS based on SHAKE
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I may be wrong, but I was under the impression that FDH did not require a source of randomness, just a hash function that would deliver a full n-byte hash.  This is highly doable with SHAKE functions.

Jim


> -----Original Message-----
> From: Cfrg <cfrg-bounces@irtf.org> On Behalf Of Peter Gutmann
> Sent: Wednesday, September 26, 2018 12:14 PM
> To: John Mattsson <john.mattsson@ericsson.com>; Saqib A. Kakvi
> <saqib.kakvi@uni-paderborn.de>; cfrg@irtf.org
> Subject: Re: [Cfrg] A new MGF for RSA-PSS based on SHAKE
> 
> ​John Mattsson <john.mattsson@ericsson.com> writes:
> 
> >If FDH gives better security it should be discussed, but based on your
> >comments it is only as secure as PSS.
> 
> Also, given recent results, neither are more secure than good old v1.5:
> 
> https://eprint.iacr.org/2018/855
> 
> Given that PSS and FDH are much, much more complex to implement than v1.5
> (i.e. more things to go wrong), and require a source of random numbers that
> v1.5 doesn't, is there any advantage to using PSS or FDH over just staying with
> v1.5?
> 
> Peter.
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