Permanent SD Card Read-Only Locker
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A package from Lithuania arrived today that may be interesting for the Infosec Community at large. Arsenijs has finally implemented a theoretical approach to program SD Cards to be temporarily or 
permanently protected from write operations.  Having reliable read-only media can be very usefully in many situations - ranging from offensive to defensive. Implants will no longer suffer from premature SD Card failures, tools like CIRClean can get an additional layer of  tamper-resistance  and forensic operations become cost-effective.


Picture of the SD Card Locker

History

This device was developed by Karl Lunt back in 2013, then improved by Nephiel in 2014. Arsentijs recently discovered it was never sold or mass-manufactured. 

New in version 2
  • Redesigned the laser-cut case to be thinner, making the "laser-cut case" locker version less bulky. It's also now transparent, except for the middle layer which is transparent orange.
  • Added usage instructions on the bottom of the PCB. 
  • Added a MicroSD slot on the bottom - it allows you to plug a MicroSD card in directly, without using any adapters. 
  • Reinforced the MicroUSB port soldering 
Common Use cases :
  • Make read-only Raspberry Pi SD cards
  • Make virus-resistant LiveCDs (or, rather, LiveSDs) for all your computer maintenance needs
  • Distribute SD cards with promotional materials
  • Forensic research and data recovery (reading from the SD card while preventing all write operations)
  • Test your SD-card-powered products for unexpected behavior (an SD card becoming read-only is a popular failure mode and tends to happen when the card controller detects severe data corruption).
Feature Set of the SD Card Locker

How does it work?

Larger SD cards have a mechanical "write protect" slide switch on the side. However, that switch is useless :
  1. not all readers support it 
  2. the OS can choose to ignore it 
  3. it's not available on  MicroSD cards 
  4. the switch tends to slide accidentally (or fall out of the SD card altogether) when you have no intention of enabling write protection.
The controller chips inside the SD cards (of all sizes, whether full-size or MicroSD) are required by the SD card standard to support a low-level command that locks the card into a read-only mode, preventing any changes - either temporarily (can be switched back to read-write) or even permanently (without a way to ever restore the write capability).

How to order ? 

You can order it from Tindie for only 12USD

Hints

  • Look into zRAM (Virtual Swap Compressed in RAM,) to move your swap into RAM Memory, this way you can still swap effectively and even use RAM more efficiently.
  • Use fstab to create directories (Like /etc/log) that only exist in RAM



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