What is the algorithm for the first part of the long 'ssid'?

The 24 byte (6 32-bit numbers) SSID (as shown with mminfo -r "ssid(54)") as stored on disk/tape is actually a 20-byte SSID. From what I have found, the format is:

Offset Description

0      - checksum

4      - type (4 for clientid, 6 for ssid)

8      - 'short' SSID

12    - savetime

16    - some counter?

20    - seems to be networker-server specific

What is the algorithm to compute the checksum?

Are the components of the 'SSID' (in particular - savetime) ever used in the internals of networker or when created, it is taken as opaque once created? (I am currently renaming the savesets, however if it is treated as opaque, I might skip this step)

I am doing some 'not nice' things to some backups and this information would be helpful...

Ondrej