Re: [openpgp] Can the OpenPGP vs. S/MIME situation be fixed?

Andrey Jivsov <> Mon, 04 July 2016 04:05 UTC

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Date: Sun, 03 Jul 2016 21:05:26 -0700
From: Andrey Jivsov <>
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Subject: Re: [openpgp] Can the OpenPGP vs. S/MIME situation be fixed?
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On 07/03/2016 08:41 PM, Peter Gutmann wrote:
> Daniel Kahn Gillmor <> writes:
>> I think we should be clear about what it would take to do what you're
>> proposing; there are two main angles:
>> * certificate interoperability (OpenPGP certs vs. X.509 certs)
> This is easily solved in a technical spec, just define (to use the approach
> I've been using in my code, which as worked more or less seamlessy for some
> years), the use of sKID for S/MIME and issuerAndSerialNumber for PGP.

Commercial PGP products used this type of "same key, two certificates" 
paradigm for over a decade. Some of this is documented in 
(that's what PGP Corp. did; this write-up is incomplete).

One issue with storing OpenPGP KeyID in X.509 Subject Key Identifier 
(SKI) is that over the last decade and earlier popular S/MIME clients 
were not using SKI to identify a recipient. Instead, they were using the 
X.509 cert's Issuer and SN. Therefore, one will have to encode OpenPGP 
keyID into the SN of the X.509 cert to be able to locate the OpenPGP key 
later from the encrypted S/MIME message. This works if the ecosystem 
owns an issuing X.509 Sub-CA, so that it's possible to control the SNs.

>> * message interoperability (PGP/MIME vs. S/MIME)
> This can't be solved by a technical spec, it's an application issue which you
> resolve by e.g. writing a PGP plugin for Outlook.
> Peter.
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