🚀 go-pugleaf

In his article, Jamie Hanrahan writes,
> Yes.  This is a nearly free way to get the effect you want.  Either RMS or
> Files-11, I forget which, keeps track of the highest block number within the
> file that's actually been written to, and the last byte witin that block
> that's been written to.  Then when you read a block from the file, any 
> bytes beyond the "highwater" mark are zeroed before you get to look at it.

This is true, but the original intent was to "send some files out".  The high
water marking wouldn't do a bit of good, because the disk (if that's what it
is) needs to be "clean" when it leaves the building.  If the disk were to fall
into "unfriendly" hands, they could mount with some other system, and read 
each block, extracting information at will.

If it's magnetic disk, there is a VMS erase pattern that can be used.
DOD_ERAPAT.MAR in SYS$EXAMPLES is the file to use, and it's not even totally
correct.  Most site security officers should know the requirements for
releasing magnetic media that has had classified info on it (declassifying).
Our site just destroys tapes.  They're too cheap to bother compromising
information while trying to save $40 or less. Disks usually require
overwriting by alternating patterns of 1's and 0's several times.  So,
high water marking is great for security on your own system, but once
it leaves your building (or system for that matter), the data onthe disk 
is fair game for anyone.

Did that confuse the issue?

Duff Browne
dab7w@virginia.edu