6   Session Key Status message (S_KS_NA_1)

Created: 14 Jan 2025

Status: Approval (Editoral)

Part: Part 5-7 (2013, Edition 1)

Links:

Page: 20

Clause: 7.3.5

Paragraph: Figure 8

Issue

The IEC 60870-5-7 overrides what is specified in IEC62351-5 regarding CLN and MAC in the Session Key Status message: CLN and MAC shall be included in the message only if the Session Key status = OK.

The value of KST indicated in CLN and MAC fields for Key Status = <OK> is 0 (zero) , however in IEC 62351-5, Par. 7.2.6.5, the value of Key Status = <OK> is 1.

Proposal

As described in IEC 62351-5, Par. 7.2.6.9, the MAC shall be included in the Key Status message even if the Session Key Status is not OK (the Session Key was initialized but not valid). The IEC 60870-5-7, Par. 7.3.5, Fig.8, should not override it.

As described in IEC 62351-5, Par. 7.2.6.6, the HAL value shall be 0 (zero), and the MAC value is not present in the message, only if the Session Key is not initialized (not available) on controlled station.

The pseudo-random challenge data shall always be present in the message regardless the current status of the Session Key.