Fixed name of COSE header parameter for countersignature

draft-ietf-ace-key-groupcomm.md

@@ -2018,7 +2018,7 @@ If source authentication of messages exchanged in the group is also ensured by m
 
 If source authentication of messages exchanged in the group is not ensured by means of signatures, then the administrative keying material conveyed in the 'mgt_key_material' parameter of the Join Response sent by KDC (see {{gid-post}}) MUST also comprise a KDC's authentication credential including the public key to use for signature verification, together with a corresponding PoP evidence. Within the 'mgt_key_material' parameter, it is RECOMMENDED to specify this information by using the same format and encoding used for the parameters 'kdc_cred', 'kdc_nonce', and 'kdc_cred_verify' in the Join Response. It is up to separate documents profiling the use of the group rekeying scheme to specify such details.
 
-After that, the KDC specifies the computed countersignature in the 'COSE_Countersignature0' header parameter of the COSE_Encrypt0 object.
+After that, the KDC specifies the computed countersignature in the 'Countersignature0 version 2' header parameter of the COSE_Encrypt0 object.
 
 Finally, the KDC specifies the COSE_Encrypt0 object as payload of a CoAP request, which is sent to the target group members as per the used message delivery method.