Run `./califrobnication > ~/file & echo $! | date` on shell server.
This will give you an exact timestamp and an approximate PID.
Next run following command locally, with a flag.txt file of length 49
`date +%s -s @<UNIX TIMESTAMP HERE> ;sudo echo <PID-2 HERE> > /proc/sys/kernel/ns_last_pid; ./califrobnication | hd`
You will get a number of different outputs
Look for one that has the last letter of flag.txt xor'ed in the same place as the } xor'ed was on the shell
Reassemble the flag