[Cryptech Tech] arm

[Peter Gutmann]

Basil Dolmatov <dol at reedcat.net> writes:

>Following some set of design rules and protocols on the bus will make this
>vector of attack us feasible.

(I assume "us" should be "less").

It doesn't work that way.  Look at, for example, this diagram:

http://m.eet.com/media/1092513/ATMEL_SAM3U_Block_Diagram.jpg

The "USB device" IP block in there will be (say) 8051 with its own ROM and RAM
implementing the USB protocol.  If you can compromise that, you have DMA
access to everything in the CPU/SoC.  With a USB/SPI bridge you'd need to
compromise the USB bridge, use that to compromise the SPI bus, and then get
across the peripheral bridge before you can get the same level of access (if
that level of access is even possible) that the on-chip USB gives you.

Peter.