Define COSE_Key_Ref

draft-bradleylundberg-cfrg-arkg.md

@@ -992,6 +992,15 @@ a reference to an ARKG private seed along with a key handle for a derived privat
 
 A COSE key reference is a COSE_Key object whose `kty` value is defined to represent a reference to a key.
 The `kid` parameter MUST be present when `kty` is a key reference type.
+These requirements are encoded in the CDDL type `COSE_Key_Ref`:
+
+~~~cddl
+COSE_Key_Ref = COSE_Key .within {
+  1 ^ => $COSE_kty_ref   ; kty: Any reference type
+  2 ^ => any,            ; kid is required
+  any => any,            ; Any other entries allowed by COSE_Key
+}
+~~~
 
 The following CDDL example represents a reference to a key derived by `ARKG-P256ADD-ECDH`
 and restricted for use with the ESP256 [fully-spec-algs] signature algorithm:
@@ -1069,6 +1078,14 @@ This section registers the following values in the IANA "COSE Key Types" registr
   - Capabilities: \[kty(-1), crv\]
   - Reference: {{cose-key-refs}} of this document
 
+These registrations add the following choices to the CDDL type socket `$COSE_kty_ref`:
+
+~~~cddl
+$COSE_kty_ref /= -65538   ; Placeholder value
+$COSE_kty_ref /= -1       ; Value TBD
+$COSE_kty_ref /= -2       ; Value TBD
+~~~
+
 
 ## COSE Key Type Parameters Registrations