Echelon OpenLDV - Manual (Page 120)

112 Extending xDriver
unique, 32-character hexadecimal string representing the 128-bit MD5 key that
is used by the RNI.
The xDriver lookup interface includes the SetNextAuthenticationKey()
method, which fills the next authentication key to be used by the RNI into the
SCO. If no change the authentication key used by the RNI is desired, the next
authentication key must be the same as the current authentication key. This
field must be filled in immediately after the current authentication key is filled
in.
After these SCO fields are filled in, the xDriver protocol engine generates a 128-
bit digest based on the current authentication key; this digest is sent as part of
every message to the RNI at the other end of the connection. The digest is
extracted by the RNI and compared to a digest produced by the authentication
key configured into the RNI. If the two digests match, then the two keys must
match and the authentication succeeds.
The current and next authentication keys filled into the SCO must match the
authentication key configured into the RNI. You can fill in an authentication key
of all 0s to use the pre-defined, default factory authentication key for the RNI as
the current authentication key. The default factory authentication key is not
secure.
Changing the Current Authentication Key
You can use the SetNextAuthenticationKey method from your lookup
extension component to change the authentication key within an RNI by filling a
next authentication key into the SCO that is different from the current
authentication key. This method initiates an incremental change to the
authentication key that is configured into the RNI, so that it will end up with the
key specified as the Next Authentication Key as its authentication key.
After this change is complete, xDriver calls the UpdateLookup method in the
lookup extension component to acknowledge the change to the RNI’s
authentication key. The lookup extension component muts implement an update
to the database from the UpdateLookup method, so that the new current value
of the authentication key is recorded in the database, and the current
authentication key in the database matches the key in the RNI. The current and
next authentication keys must always be stored in the database, and can only be
updated when the UpdateLookup method is called.
Table 36 on page 113 describes the flow of events that occurs when the next
authentication key field is used to update the authentication key of an RNI. In
this example, the lookup extension fills different MD5 authentication keys into
the current authentication key and next authentication key fields into the SCO.
The table uses a sample authentication key (such as ABCD) that does not use the
required format.