[Cryptography] The Crypto Bone's Threat Model

[Peter Gutmann]

Jerry Leichter <leichter at lrw.com> writes:

>Note the "supposed to be".  Unfortunately, support for write locking is an
>optional part of the SD standard.  Devices are free to ignore the lock.  If
>you want to rely on this feature, you need to choose your SD card reader
>carefully.  (I have no idea how widespread support for the feature actually
>is.)

On the occasions where I've run into it at a low enough level, the lock is an
opt-in rather than opt-out, so the reader has to specifically include code
like:

  if R/O tab set -> return EACCES

On one occasion we got some rather baffled looks from an embedded-systems
vendor whose devices would happily write all over write-protected SD cards.
It was a *feature*, if the field engineers forgot to slide the tab into the
correct position the system wouldn't shut down due to lack of writeable
storage.

Peter.