[Smcwg-public] On the subject:serialNumber attribute

Dimitris Zacharopoulos (HARICA) dzacharo at harica.gr
Wed Apr 13 07:02:48 UTC 2022

On 4/4/2022 1:02 μ.μ., Adriano Santoni via Smcwg-public wrote:
> Hi all,
> I have some doubts about this part, in connection with IV and SV 
> certificates:
>> * Subject distinguished name fields*
>> g. *Certificate Field*: subject:serialNumber (
>> *Contents*: If present, the subject:serialNumber MAY be used to 
>> contain an identifier assigned by the CA or RA to identify and/or to 
>> disambiguate the Subscriber.
> I'm rather dubious about "an identifier assigned by the CA or RA" 
> being appropriate. Unless a pseudonym is used, the Subscriber identity 
> should be clear to Relying Parties without a need to query the CA or 
> RA, which would however be necessary if such identifier was assigned 
> by the CA or RA and the certificate contained no other disambiguating 
> information.
> How about we decide, instead, that the subject: serialNumber MAY 
> contain, for disambiguating purposes, a unique identifier of the 
> Subscriber assigned to him/her by a government agency? It could be 
> taken from the identity document that has been verified according to 
> section 3.2.4 (Authentication of individual identity ) and encoded 
> according to ETSI EN 319 412-1 Section 5.1.3 (e.g. IDCxx-nnnnn, 
> PASxx-nnnnn, TINxx-nnnnn and so on).
> Apart from this, it seems to me that the purpose and requirements of 
> this attribute are not very well explained in the various cases (MV, 
> IV, OV, SV). For example, since the organizationIdentifier attribute 
> is mandatory in the OV case, what would be the use of having the 
> serialNumber in the subject as well?
> Adriano

Sorry if this has already been discussed in S/MIME calls.

Adriano, I don't think this is the situation today. According to ETSI, a 
CA is allowed to use a unique identifier in the subject:serialNumber 
field to disambiguate a natural person in collision cases. The use of 
TIN, IDC, PAS, etc is obviously allowed but not the only way to add a 
serialNumber. In fact, the use of these cases are associated with the 
semanticsIdentifier of the qcStatements. You can totally avoid that 
today and be compliant with the ETSI profiles.


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