Looking at the PCB & Chips – Hardware Wallet Research #2

So in the previous video we talked a bit more
highlevel about what a hardware wallet is, but now it’s time to have a look at the
actual device. So this is the Ledger Nano S. I have to say, a pretty cool looking device.On
one side it has the Ledger Logo and on the backside it says “vires in numeris”, which
is fancy language for “strength in numbers”. SO LET’S HIT THE SUBSCRIBE BUTTON TO GET
THAT NUMBER UP! Just kidding. So from the outside the Ledger has two buttons
to enter the pin and change settings and so forth.

A screen to display different kinds
of information and menus and a usb port, to connect the device to your computer so you
can actually do cryptocurrency transactions. Here I was just testing it out, setting a
secure pin and let it generate a private key, and I’m writing down my mnemonic backup
phrase. So yeah it seems to work. On your computer you will actually have a software
running that interacts with the Ledger. The Ledger Manager is actually a Chrome app. So
before I was updating the Ledger Nano I actually made sure to open the Chrome Developer Tools
to observe requests the software maybe makes to the internet. Mostly I was interested in
if the firmware is downloaded and if we can grab the firmware update through that. So
I left that open when I did the update.

Now don’t get excited and think, “oh gosh
a chrome app and you can debug it so easily, how awful”. It’s not. This hardware wallet
is supposed to protect you against malware on your PC, so the software running there
should not really matter. Also I don’t consider further obfuscation really helpful, especially
because I want to actually understand what the device I bought does. Rather than spending
countless hours defeating obfuscation. So I’m big fan of that choice.
Anyway, we are much more interested in the hardware for now and we will come back to
the Chrome app later. I just wanted to mention it because timeline wise, that is what I did
before I opened up the Ledger. Okay… we can remove the metal case very
easily, but to open the plastic case we need some tools. Urgh it kinda hurts to just having
spent around a 100$, and only a few hours later you trying to pry it open and hoping
not to break it.

So opening up is easy, there are just a few hooks in place and maybe you
could snap one off accidentally, but in general it seems pretty straight forward.
So here you can see the USB socket, some chips and a flat cable wrapping around to the other
side. That’s the display connector. Also don’t get annoyed when I just show
different shots of it, I just spent around 1500$ on a Camera and Lenses just because
I was so excited for this opportunity to make these videos that I wanted to have great shots.
And I have no clue what I am doing but I think it looks good.

So appreciate them.
Anyway, we can simply push out the pcb and screen, it’s not glued in or anything. So
here you can see the flat cable bending around to the screen and here are the two buttons.
Here it is from the bottom side. We can already see some very interesting looking points.
These TP numbered points are probably Test Points. When you manufacture hardware you
often expose test points, that are not necessary outputs for debug interfaces or anything,
they are usually just a way to verify that the assembled hardware works.

So you can have
an automatic device coming down with some needles, and running some tests on it. Very
normal. But there are also a few unlabeled points over here, and to those we will get
to soon. On the front side we have three chips, one
with a lot of pins and then two smaller ones. But now you have to say bye to my beautiful
shots for a while. Unfortunately a lot of hardware research is done through documentations
and manuals, so please excuse me for stretching this moments with no content and useless talking
in order to show more footage from my 1500$ camera setup. A pcb might look very intimidating and you
feel like you have no clue what to do now, this is just dark magic, but there is always
stuff you can do. Most chips, especially on typical small devices like this are nothing
special. They are bought from huge manufacturers and you can just look up what these chips
are for. You don’t need to understand how to build hardware with them in order to get
an understanding of what does what. The most prominent and biggest chip here is this one.
And when you google the first cryptic number here “f042k66” you find a bit of information.
I mean the ledger is a known device using this chip so many other people have documented
that already, but let’s assume these results weren't here, because it’s a different device,
then you find some traces about “stm32 f042k6”, the last 6 is missing so when you search for
that the results are a lot clearer.

STM32 F042k6 is an ARM chip. And on the official
information page of STMicroelectronics you can also find the STMicroelectronics logo,
the ST and it’s here on the chip. So yeah, pretty sure that’s the chip, or at least
from the same family. So it’s very likely the documentation you find here is very relevant.
This is just a very typical microcontroller.

Actually it’s ARM, so it’s a different
architecture from the microcontroller we have seen before on this channel – that was AVR.
Anyway. So this is a ARM 32-bit Cortex -M0 CPU, Runs with up to 48 MHz. Has 16 to 332
Kilobytes of Flash Memory, so that’s basically persistent memory where the program code is
stored and 6 Kilobytes of SRAM. So RAM. So there is not much RAM on there. Other interesting
features for us might be that it can speak USB, it has two serial connections, and we
know serial, we have used serial several times before with the AVR stuff.
And it supports the serial wire debug protocol. SWD. mhmh… stuff like that is obviously
very interesting for research. But let’s move on and have another look
at the board. Do you see here these two lines going from the USB to the microcontroller?
So it looks like USB is directly communicating with this ARM processor.

And the one button
here looks also to be directly connected to this chip. So this chip seems kind of to be
the main component. It handles the USB communication, the button presses and looks like these lines
here are also connected to the display? So seems like it also controls the display.
Also now that we know the ST logo, we know this second chip here is from the same manufacturer.
But when you try to search for those labels, you can’t really find anything. Also is
that NBO, NB0, N8O, N80? As you know I’m not super into electronics, so I can only
speculate. And I assume this is a generic label because this is actually the secure
element.

On the ledger wallet website it states that
two chips are used, the STM32F042, which we already identified, and the ST31H320 (secure).
There is only one other chip here under the display cable and that one is also from ST
and it’s a ST8R00W, which is a syncronous (TYPO! TYPO! Missing ‘h’. Literally a
garbage product). It’s a boost converter with output current cut-off function.

No idea
what that is, but it’s doing some electronics magic, maybe it’s required to drive the
display. As you can see it’s just an analog component and not a digital microcontroller
or so. So this means this one has to be the secure element – the ST31H320. This chip is “Designed for secure ID (so
for secure identification) and banking applications. (So for example this could be inside a smart
card, like your typical baking chip card and you can identify yourself to the bank), the
ST31H platform products are serial access microcontrollers (which I think means it communicates
via a serial interface with other components) that incorporate the most recent generation
of ARM processors for embedded secure systems.

Their SecurCore® SC000™ 32-bit RISC core
is built on the Cortex™ M0 core with additional security features to help to protect against
advanced forms of attacks.” In hardware speech a “core” is basically
like a library in software. Chips are designed through their own design languages, like programming
languages, for example VHDL or verilog, and we have used verilog once before on this channel
to implement something simple. So These design files, or libraries basically, can just be
licensed by somebody, and then they are allowed to go with that design to a manufacturer plant
and they have then machines that produce chips that contain this design.

And if you have
heard of FPGAs before, they are like reprogrammable chips, so you can implement your own chip
or license cores for your FPGA and configure the FPGA with ii. So ST licensed the SecureCore
SC000 RISC core, which is based on the Cortex M0 core. Basically a library based on another
library and they pay tons of money to be allowed to manufacturer a chip with those. This means
you can also look up some information on these cores because companies might want to license
these from ARM. And yeah, the Cortex M0 is just a general very small ARM processor, " small
silicon area”, so it doesn’t take up much actual space on the chip.

And the Arm SecurCore
processors are the most widely licensed 32-bit processors for smartcards worldwide. So I
obviously don’t know if any of the smartcards I have here use this chip, but totally might
have one. But, the “explanation of anti-tampering features requires a SecurCore NDA.” a non
disclosure agreement with arm. So without anybody leaking this or researchers trying
to reverse engineer it, the public won’t know how exactly it’s supposed to protect
you. From hardware security classes at university I also got a great tip, you should research
a bit the pay TV hacking scene around smart cards, there are some nice documentaries,
and what kind of crazy (and expensive) attacks exists to get access to the secrets stored
on these chips. But let’s go back to the insecure STM32
for now and start by having a look into the official ledger documentation which is really
great and goes into a lot of detail. I want to highlight a sentence in Chapter 10.

There are “two hardware chips, one being
secure (the ST31 Secure Element), and the other having JTAG enabled and acting as a
proxy (the STM32 MCU).”. JTAG. That sounds awesome… We will have a look
at that next video.

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