Date: Wed, 14 Jun 2017 03:28:29 +0000
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To: dcrup@ietf.org
From: Scott Kitterman <sklist@kitterman.com>
Message-ID: <BFDFAA4E-F253-497A-9881-D2223B45037A@kitterman.com>
Archived-At: <https://mailarchive.ietf.org/arch/msg/dcrup/aj4b5tTjwe8t_HQEBPiHH_W16G4>
Subject: Re: [Dcrup] rsa-sha1 usage
Precedence: list



On June 13, 2017 11:20:42 PM EDT, Jim Fenton <fenton@bluepopcorn=2Enet> wr=
ote:
>On 6/13/17 8:16 PM, Murray S=2E Kucherawy wrote:
>> On Tue, Jun 13, 2017 at 6:55 PM, Jim Fenton <fenton@bluepopcorn=2Enet
>> <mailto:fenton@bluepopcorn=2Enet>> wrote:
>>
>>>     That being the case, why do we think people will pay attention
>to
>>>     a MUST NOT today?
>>
>>     Because implementations will stop supporting rsa-sha1, forcing
>the
>>     issue for any who upgrade=2E I'm all for having them stop
>supporting
>>     signing with rsa-sha1, but they should continue to support
>>     verification for a while=2E
>>
>>
>> We can't have this logic both ways=2E  Scott claimed nobody pays
>> attention to the advice in RFCs ("Operational practice=E2=80=8B isn't c=
losely
>> coupled with standards changes")=2E  If that's true, then there's no
>> meat to a MUST NOT anyway, and it really only matters what people
>will
>> implement=2E  And if that's true, then saying current implementations
>> neither sign with nor verify "rsa-sha1" because it's deprecated
>> suffices, and we're done=2E
>
>Based on no supporting data whatsoever, my conjecture is that
>implementers pay a lot more attention to what RFCs say than people who
>are deploying others' implementations=2E Which basically boils down to
>MUSTs having a significant effect and SHOULDs having little=2E Which is
>why I favor making signing with rsa-sha1 a MUST NOT prior to making
>verification of rsa-sha1 signatures a MUST NOT=2E
>
>-Jim

I agree on the importance of MUST versus SHOULD to implementors=2E  In gen=
eral terms, MUST tells me what I have to implement and SHOULD tells me the =
defaults=2E

I still think we should MUST NOT both signing and verification for rsa-sha=
1 if for no other reason than to not require implementations to support thr=
ee algorithms, but I am starting to get the sense I'm in the rough on that=
=2E

Scott K