How can I get the CommonName of a certificate?

[lecanard539]

Hi! Thanks for making this crate.

I successfully decoded a rasn_pkix::Certificate, and I can debug-print the tbs_certificate.subject, and I can see that there is a CN because there is an entry with OID 2.5.4.3. I can also see that there is a CommonName struct in the crate. But I don't see how I'm supposed to get at the information inside of Subject.

How can I get an instance of the CommonName struct from a certificate subject if present?

Or more generally, how can I get instances of the appropriate types for the things inside of subject?

Thanks!

[Nicceboy]

Hi, have you checked the type RelativeDistinguishedName and AttributeTypeAndValue https://github.com/librasn/rasn/blob/main/standards/pkix/src/lib.rs#L518, when you follow the types of tbs_certificate.subject ?

Basically, the subject contains oid-value pairs, where AttributeType is ObjectIdentifier and AttributeValue is the corresponding value of that attribute.

The value of matching attribute OID is encoded according to type definition.
CommonName is actually legacy type - type with OID 2.5.4.3 is defined in standard in page 112 as

-- Naming attributes of type X520CommonName

id-at-commonName        AttributeType ::= { id-at 3 }

-- Naming attributes of type X520CommonName:
--   X520CommonName ::= DirectoryName (SIZE (1..ub-common-name))
--
-- Expanded to avoid parameterized type:
X520CommonName ::= CHOICE {
      teletexString     TeletexString   (SIZE (1..ub-common-name)),
      printableString   PrintableString (SIZE (1..ub-common-name)),
      universalString   UniversalString (SIZE (1..ub-common-name)),
      utf8String        UTF8String      (SIZE (1..ub-common-name)),
      bmpString         BMPString       (SIZE (1..ub-common-name)) }

(X520CommonName) in this case, so you would need to extract that value and then decode it as X520CommonName type.