3.2.1.4.3.2.12 PropID = 0x0000000C (CR_PROP_CASIGCERT) "CA Signature Certificate"
The client has requested a particular signing certificate.
The CA SHOULD retrieve the CA certificate from the Signing_Cert_Certificate column in the row indexed by the value of the PropIndex parameter. The CA MUST return the signature certificate in X509 format, as specified in [X660]. The CA MUST return the value through a CERTTRANSBLOB (section 2.2.2.2) structure.
Marshaling rules for the CERTTRANSBLOB structure are specified in section 2.2.2.2.