Secure Shell

[clark.wbst at PARC-MAXC.ARPA]

I did it to the V6 shell by simply changing all system calls from
write to write1, etc.  My system calls then analyzed the arguments 
and bombed out if it did not like them.  This consisted mostly of
passing only path names starting with the login directory name,
a system wide 'bin' with safe commands, modified like the shell,
and any path not starting with / and having no .. in it.  Since
ln was not available, and no development tools, they could not
make their own programs, other than by the far fetched way of
typing the object in.  I used it to give lab practicals.

--Ray Clark