[Servercert-wg] Ballot SC17 version 3: Alternative registration numbers for EU certificates

[Ryan Sleevi]

On Fri, Apr 5, 2019 at 3:02 PM Erwann Abalea via Servercert-wg <
servercert-wg at cabforum.org> wrote:

> EUPSD2AuthorizationNumber ::= SEQUENCE {
>
>   registrationSchemeIdentifier   PrintableString,
>
>   registrationCountry            PrintableString,
>
>   registrationStateorProvince    PrintableString OPTIONAL,
>
>   registrationReference          PrintableString
>
> }
>

The optional value should be (implicitly or explicitly) tagged, correct?
Otherwise, it seems you won't be able to know whether you're reading a
registrationStateorProvince or a registrationReference until you determine
whether or not the following element is valid - that is, whether you have
three or four elements.  Since the point of ASN.1/DER is to avoid these
context-dependent parsers, which is inherent in the deliminter-separated
string being proposed, I suspect the modification (with implicit tagging)
should be

EUPSD2AuthorizationNumber ::= SEQUENCE {
  registrationSchemeIdentifier   PrintableString,
  registrationCountry            PrintableString,
  registrationStateorProvince    [0] IMPLICIT PrintableString OPTIONAL,
  registrationReference          PrintableString
}
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