[Cryptography] Ex-CIA Joshua Schulte Describes His Data/Crypto Hiding Prowess

[Jon Callas]

> On Mar 4, 2020, at 10:56 AM, Jeremy Stanley <fungi at yuggoth.org> wrote:
> 
> Solid state storage devices typically have some (one reference I
> found suggests 7.3%) of their physical blocks hidden in reserve to
> accommodate reshuffling around bad blocks and to ease transparent
> wear levelling. The "physical" block addresses to which your
> operating system's device driver writes aren't all the actual blocks
> on the device, nor even the same actual memory locations each time
> you "fill up" the ones it tells you are there.

That is indeed one of the considerations -- spare blocks for remapping -- and even rotating media does that these days. Drive makers have huge incentives to push what's possible, and large numbers of spare blocks cover many sins. It also gives a mechanism to signal to the OS or diagnostics that the drive is failing but not yet failed. 

Remapped blocks are almost generally being fussy about being written, but still can be read. Thus they have potentially dangerous data that cannot erased. 

On all bleeding-edge technologies, it's hard to say anything definitive because they're actively changing. My understanding is that SSDs in particular are still so bleeding-edge (especially in high-capacity, high-speed cases) that extrapolation from any isolated fact is hard. From rumors I have heard, your 7.3% seems on the low side. I've heard loose talk that some high-reliability drives might be much, much higher, particularly when there are manufacturing changes.

For example, let's suppose we have a manufacturing line that makes 2TB "datacenter" drives and another one that makes 6TB "desktop" drives. Let's also suppose that each drive costs $50 to manufacture and sell fors $150. Now let's suppose we want to start to build 10TB drives with a new process. If we put new firmware on the 6TB drives so that they have 2TB active storage and 4TB of spare space, we can almost certainly hit the reliability metrics of the datacenter drives using the same guts as the desktop drives. That's the sort of crazy talk I've heard that sounds plausible and while I have a raised eyebrow, I've seen wackier things in my day.

	Jon