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From: John Bradley <ve7jtb@ve7jtb.com>
In-Reply-To: <546A1E4E.8020906@cisco.com>
Date: Mon, 17 Nov 2014 12:25:08 -0500
Message-Id: <A5EC5B4B-DB79-48BA-AE87-93D5897A4AA7@ve7jtb.com>
References: <CAL02cgToqHMvpeXdvnRTf7PEpvsbZf+kP7zM5i=r5rzJP86wCA@mail.gmail.com>
 <4E1F6AAD24975D4BA5B16804296739439BB7A9E3@TK5EX14MBXC286.redmond.corp.microsoft.com>
 <546A1E4E.8020906@cisco.com>
To: Matt Miller <mamille2@cisco.com>
Archived-At: http://mailarchive.ietf.org/arch/msg/jose/rucRPA_b6A83s3exOVelC8zahsM
Cc: Richard Barnes <rlb@ipv.sx>, Michael Jones <Michael.Jones@microsoft.com>, 
 "jose@ietf.org" <jose@ietf.org>
Subject: Re: [jose] Clean interop with "oth"
Precedence: list


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I think using multi prime is about 7 to 9 times faster in decryption =
than regular RSA decryption (depending on implementation).

What I don't know is how much slower a key with r > 2 is when only using =
d is vs the standard case of using d where r =3D 2.

I think looking at key generation that they are the same, but someone =
smarter than me needs to confirm that.

As I recall the idea behind multi-prime was to speed up decryption to =
make RSA practical on mobile platforms of the day. (the alternative =
being EC)

That is less of an issue now given speed improvements, though might now =
be an issue for IoT platforms (I suspect they are all using EC anyway).

If using d is a significant enough slowdown that it can be a denial of =
service attack then perhaps the decrypter shouldn't be using RSA keys in =
 the first place.

If decryption using a multi prime private key only using d where r >2 is =
the same as or similar to decryption using d where r =3D 2 then I would =
go with Mike's wording,  but add a security consideration around the =
performance issues with RSA decryption if people think that is required.


John B.
(PS this math stuff makes my head hurt so I may be completely wrong)



> On Nov 17, 2014, at 11:11 AM, =E2=8C=98 Matt Miller =
<mamille2@cisco.com> wrote:
>=20
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA512
>=20
> Technically, only the private exponent and the modulus are necessary
> for the private operations.  However, the performance can be so bad
> that it be a Denial of Service attack.  Better to reject, in my =
opinion.
>=20
>=20
> - --=20
> - - m&m
>=20
> Matt Miller < mamille2@cisco.com >
> Cisco Systems, Inc.
>=20
> On 11/10/14, 10:08 PM, Mike Jones wrote:
>> Clarification question:  Would the private key operate correctly,
>> if possibly inefficiently, in the multi-prime case if all the
>> private key parameters other than =E2=80=9Cd=E2=80=9D were ignored?  =
I ask, because
>> if this is the case, your wording could be modified to the less
>> severe text:
>>=20
>>=20
>>=20
>> If the consumer of a JWK does not support multi-prime RSA moduli
>> and it encounters a private key that includes the "oth" parameter,
>> then it MUST either reject the key or ignore all the private key
>> parameters other than =E2=80=9Cd=E2=80=9D.
>>=20
>>=20
>>=20
>> -- Mike
>>=20
>>=20
>>=20
>> *From:*jose [mailto:jose-bounces@ietf.org] *On Behalf Of *Richard
>> Barnes *Sent:* Monday, November 10, 2014 7:02 PM *To:*
>> jose@ietf.org *Subject:* [jose] Clean interop with "oth"
>>=20
>>=20
>>=20
>> It seems clear that there are no implementations today that support
>> the "oth" element, i.e., that support RSA with a modulus with
>> multiple factors.  At least some of them simply ignore the "oth"
>> element, which unfortunately leads to incorrect operation.  I would
>> propose something of the following form in JWA:
>>=20
>> """
>>=20
>> If the consumer of a JWK does not support multi-prime RSA moduli
>> and it encounters a private key that includes the "oth" parameter,
>> then it MUST reject the key.
>>=20
>> """
>>=20
>>=20
>>=20
>> _______________________________________________ jose mailing list=20
>> jose@ietf.org https://www.ietf.org/mailman/listinfo/jose
>>=20
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>=20
> _______________________________________________
> jose mailing list
> jose@ietf.org
> https://www.ietf.org/mailman/listinfo/jose


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