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yay hi there so it's a pleasure to to
speak here
um yeah so I'm still waiting for the
confirmation that I'm being streamed
right now does it
work everything
is delayed
okay I seem to be live great um so it's
a pleasure to be here um and talking at
the Dalk so the digital uh C3
walk um and so I will be talking about
Bluetooth random number generator which
is a topic I was working on together
with M deala and he did it as a master
teaches and afterward I continued it
um so um
the question is always um how do things
work like in terms of uh what does
Randomness look like and I found this
nice rabbit on the internet and it might
give you some Randomness but uh yeah
that's the big question is it really
random what you get there or is it not
random
um and uh then Mara asked me if he can
do a master teases with me and back then
when he started I had something like 10
students and I was like oh you know I
have tons of students already working on
Bluetooth and I don't really know what
to give you because someone is like
putting it to Linux another person to me
and so on uh I don't really can paralyze
more there and then he was like but I
really want to do Master tees rev you
and then I was like huh yeah so I still
I still have this random number
generator thing um that someone really
should look into um and so um yeah he
started doing a masteris with me
um now the big question is like why is
it even interesting to look in a random
number generator so um if you look into
the specification the specification says
that the random number generator really
needs to be fips compliant because it is
used for um authentication encryption
and everything else that's somewhat um
related to
security so um that means that security
breaks sorry I'm I'm still confused with
the Mumble I'm
sorry
uh okay so um the the random number
generator is very important for security
for encryption um but also for um
authentication and everything that does
security and so it needs to be fips
compliant which means that it needs to
pass certain statistical tests and the
specification also says like that you
should replace the sh one function by sh
256 and so on and proposes some tests
that should be done with the random
number
generator um now the big thing is even
if a random number generator is passing
statistical tests it might still um be
broken so just if it doesn't pass the
test then it's obviously broken but even
if it passes the test there might still
be something going on so it might still
not be cryptographically strong just
because it's passing some
tests and now the big question is in a
Bluetooth chip how can you acquire
Randomness so there is multiple
possibilities um I don't know so I I
asked my unicorn so and of course my
unicorn is here as always um so and now
the big question to the Unicorn is how
do you acquire Randomness um so there
might be first of all the answer to
everything which is 42 or then there is
another thing that you might have heard
about which is um the random access
memory and probably nobody heard about
the um random only memory and then there
is another option which sounds safe
which is the hardware random number
generator so that's a few options um and
still so I didn't have the answer my
unicorn didn't have the answer so I
asked the internet Joker which is
Twitter and I made a poll um so that
everyone who knows infos SEC can um
check it out and then I was looking for
the answers so what was the top answer
yeah 42 is the top
answer um but then some people also
heard about Hardware random number
generators and some said random access
memory and probably nobody ever heard
about the random only
memory so let's see um yeah so how is it
implemented actually um so what what um
M deala looked into is uh the following
four devices the first one is the Google
Nexus 5 which is just like our let's say
hacking device in those terms that is
the first one where we got nexmon and
everything else working
um and then we have three more uh
devices listed here because we have
symbols for them so it's only partial
symbols just some function names and
Global variable names but that's way
more than just nothing because the
Bluetooth firware really doesn't have
any
strings and within those four devices he
was already able to um differentiate
between two variants uh the first one
has an inline super random number
generator but also Hardware number
generator um and no cache and the second
variant somehow has a cache and some
little rewrite in the library thought
that the random number generator uh the
random number generator is um somehow
outlined in a in another function
um
so and how does it look like so the
variant number two is just the code
that's also in the variant number three
for the hardware number generator it
just checks um if the hardware random
number generator is ready and if it's
ready um then it's basically just
checking uh if it has a new number so it
also Pets the watch do in between
because just waiting for a new random
number might take a moment so that the
chip doesn't Crash from this and then
returns a four byte value with the with
the data so that's it very simple just
wait for the next random number and it
has also some constant just to check
like if there is really hard random
number generator present and if it has a
new number and so on but that's just
magic
numbers yeah so um that's that's the
basic setup and then the pseudo random
number generator is way more more
interesting because it's taking a few
values um so the values basically are
the Bluth clock the Blu clock is value
that is shared for communication to all
parties then there is the uh local clock
of the device and then there is a few
more values which have to do with signal
processing and it's taking all those
values and putting them into the not so
secure crc32 functions um just to
compress it back to for bytes so that
somehow the combined entropy of
everything of this is combined back to
the four bytes that we need for the um
random number uh function so it looks
just the same no matter if the one or
the other is called um and so another
input is the previous P random number
but um if it's initialized then um
instead it's taking some memory but
that's that's basically the the only
difference
here
so this this one looks a bit strange so
really not the thing that you want to
see um because like signal inputs might
be predictable and clocks especially are
predictable and CSC 32 also does not
look too good um so what he did there
was doing a few more measurements and so
the measurements really didn't look good
the the plots here are um histograms and
each histogram has just the Valu 0 to
255 which means so the ploth clock for
example is actually Four bytes and then
of course one of the values is more
frequent uh because that's like one of
the digits of the clock and so on so
it's not really a Time plot here or
something here was just looking at the
bite frequency and the only thing that
looks random is this plot age the last
one which is the last random value so if
it would only use um the Pud random
number generator then this would be the
end entropy that theud random number
generator
gets um and then it was already the end
of his thesis and we reported this and
what I currently do is I first uh
request a cve at Mitra they just take
one or two days and then I send it to
broadcom and Cypress and their customers
because um this takes so until broadcom
replies it usually takes a week or
longer so um and they also don't issue
any cve they don't issue any issue ID or
something so if I don't request the cve
in advance myself then I cannot really
track the issue so that's that's why we
do it this way which also confuses then
the the customers of broadcom because
they think broadcom would assign those
CVS but they
don't um yeah so then we did responsible
disclosure and um we said so yeah so why
would you introd produc this to the
random number generator which really
doesn't look good um if you had a proper
Hardware random number generator and
then broadcom said like why should we
ever go to the pseudo random fallback if
we have the hardware in the device so it
was just like everyone claims like yeah
you did you did a mistake but uh nobody
really said like and this is this is the
mistake so uh it was just going forth
and back and broadcom said yeah we we
never ever go to defa back uh so it's
safe
and yeah so this is then probably the
end because mesus was finished so he
handed it in so no pingy used in any of
the devices he looked into um nothing to
see there and then we just say goodbye
and this is the end so to say uh the end
in terms of um yeah um everything
everything is great and uh everything is
secure and nothing is bad and now um the
cool thing here is that now um my other
student former student Yan will have a
lot of time to explain all the weird
machines and remote code execution to
you right because we are just like uh 10
minutes or something in my talk um but
this is this is only half the truth so
uh this is not really the
end because then of course um I looked
into a few more
devices because some if they if they
have a fallback and even the code
changed over time then there should be a
reason why they change the code over
time and of course you should also
measure the hardware random generator
itself um so if it's really secure and
the basic tests don't need so much data
but if you take the DI harder test Suite
it means that you need to get one
gigabyte of random data out of this chip
of a UI it with some pet and it should
be as fast as possible and so on and so
forth so this this was really
pain um so what did I do first of all
you need to try to find a large free
memory area um in the chip while it's
idle and I found some on most chips so
it depends a bit so different chips
different measurements some of them had
smaller regions um and then I also
wanted to be sure that no other process
is writing into the memory area because
actually the area is not really free
it's just currently not being used um by
uh another
process and hopefully not used by
another process so I was just using the
fifth bite to write some test bite
because the process usually writes like
in a sequence and so on so that's what I
did as sanity check and I also
deactivated the original RBG Rand
function so that they are that this is
not called in the
background um and falsifies my
results and then the next thing is that
I did some asynchronous call back so
that I don't pull for data all the time
but I wait until the measurement is
finished uh which makes it a bit faster
but so for this you need to fix the Lou
rum and some HCI call back and stuff and
these were broken on a few devices so
it's somehow broken on the Nexus 6p and
iPhone 7 and it's in another way broken
on the Cypress evoluation boards and
yeah well they removed Lounge RAM on the
iPhone 11 but so except from that so
on most devices it it works some devices
need like certain
patches uh yeah so and then finally I
had like some data from those chips and
really like a gigabyte or more and then
I was like okay it's it's just random
data I really don't care about it so I
just upload it to the the Google Cloud
because who cares um and then it just
locked me out and so on and so forth but
I could log in again but it's like not
what I usually do like putting a lot of
data uh to
Google and then Felix just said like
next time when I do this I should maybe
not call it random data do bin but maybe
encrypted backup. bin would be a funnier
name so the reason the reason why there
is so much data for the Nexus 5 is
probably because I put my backup in
there um yeah so this is the data um you
see 2.7 gabt for the Nexus 5 that's
where my encrypted backup is contained
and all the others are the random
numbers and all of them pass the die
harder
tests um and then there is still some
chips that are too much pain so first of
all I have this uh iMac late 2009 which
basically has a 2007 firmware or
something and it's so slow and it has so
little free memory that you really can't
forget to get data out of this
chip and then there is the Samsung
Galaxy S10 and there they introduce
dearies and stuff so like it just gets
more more pain to write patches and the
iPhone 11 currently is not supported by
internal blue so I need to write
everything with blue tool by hand so
really like enter the hex numbers each
and every one after the other um but
what I did for those devices is that at
least confirmed that there is a hardware
random number generator and that when I
do actions that trigger it um like
pairing and stuff that the number in the
hardware R number generator is changing
so at least there is one present but I
didn't collect like one gigabyte or more
of
data um yeah so now the issue is so
there's tons of variants and the firm
very itself um it's just a raw
binary and that really makes it a lot of
a lot of pain because every mistake that
you that you get um when you try to find
assembly and just find the wrong arm
instruction beginnings and so on and so
forth um every mistake will make um an
error in the call graph and then um you
will get wrong matches so for um Ida 68
the disassembler is a bit more
aggressive and I think it's linear and
then there is an Ida 72 and your on it's
doing it a bit different and then you
have less false positives but it's also
finding less and then there's Amnesia
which is also way too aggressive so if
you have too many um like false
positives uh you get problems if you
don't find all of the functions you also
have problems so it's it's really it's
really pain um and so I have a student
who developed another tool that's not
looking for this assembly but just for
raw binary stuff and that's going to be
released soon but um I also couldn't use
this one there because if you have
different compiler options and stuff so
if you go over a lot of year years uh in
fare
versions then this one also doesn't work
that well it works well for patches
within the same chip and so on but it
doesn't work well for going over 10
years of
firmware uh yeah so the variants um the
oldest variant is the one in the iMac
and also the Asos USB dongle um and the
Pud random number generator fallback um
looks very funny because it really just
depends on a clock and the clock is
incremented each
0.005 seconds by one and that's it so um
the P random number generator there is
really really really bad but also at
least on the IM L 2009 it's not being
used I currently didn't have an Asus USB
dongle to confirm so I just looked into
the F
image um yeah so then there is tons of
more tips of the variant two and three
which are the pseudo ramom number
generator that I just showed to you um
still what you can see here is that the
location of the the mapping of where
this Hardware register is changed um and
so it changed a bit over the years but
then forth and back so the the chip date
the compile date is not always
necessarily exactly what the memory
mapping is and so on and so forth
um yeah then there is variant number
five and variant number five is the one
that you can find in the current um
iPhone 11 but also the iPhone 8 XXR I
don't have a f redump of the chip of the
iPhone XS it's a different one um and
then also the Samsung Galaxy S10 s20 um
they all have this newer variant and the
new variant is a rewrite of this
complete uh random bite generator
Library so it's a everything is
different inside and it has some kind of
asynchronous catch and so on um but uh
it's still using this uh library in the
same way so it's still using the same
calls that I will show you later in a
call cph and what they did is they
removed the pseudo random number
generator at least from what I could see
I mean it's always hard to say because
um there's also like patches and a lot
of other stuff so I could still be
missing something in a firmware without
any symbols and so on and so forth but
it looks like they they skipped the
pseud random number generator which
means if in one of those uh firmware
versions um the hardware random number
generator would be wrong in some way
then there wouldn't be any fallback
which might also not be
good yeah and then there is the variant
number four because I I can count I just
skipped variant number four and the
variant number four yeah somehow they
forgot the hard random number generator
so one of all those devices that I
looked into was actually missing it and
it's obviously the number four because
uh yeah it's probably a bit like the dbn
random number generator which is also
returning four all the time
so um and now if you look into that
device that is missing um the hardware
random number generator we have the same
pattern as in the variant number two so
um we have the previous random value we
have two clocks and we have some um
signal based
inputs um so now the first one the clock
um you can see so this is a measurement
really over uh 50 minutes just looking
into the bluo clock and the heartbe
clock and the heartbe clock starts at FF
FF f f FF and then the Pluto clock
increases the bluo clock itself is
shared over the air um but it might be
reset so they might not so they
correlate but they might not have like a
corresponding value so you still as an
attacker would need to figure out what
the current local um Hardware clock of
the device is um but you might also be
able as an eer to set this so if you
crash the the Bluetooth chip um then it
starts again at FFF F
FF which means um that now crash only
attacks which broadcom is usually not
patching become relevant again and this
is this is really sad so it means a very
simple um crash only attack in whatever
state machine entering some weird state
or whatever that is no memory bug um but
crash is the chip can already be
relevant um to reset this
um yeah and now there is signal
processing inputs so there is a register
called dcfh out and on the left hand
side you can see it's um getting just
values between one and 80 something
around this and on the right hand side
you can see that also um over time it's
not really random but you can see a
pattern so it stays a bit of the time
the same and then the numbers that
follow each other are somewhat similar
um so it's also not really best random
input
there and then there is two more that
are a bit random the first one is thex
init angle um which only takes a few
values if you measure over time and the
second one um is the HC status I think
it's somewhat like RSSI but um so in the
first measurement it was really zero all
the time in the second measurement it
was sometimes zero sometimes getting
values but also just values in the same
range um so it's again not really
random which altogether means that if
those inputs are not random and an eer
um gets the current value of the RNG um
the attacker might be able to predict
the next values of the
RNG now the question is so why did we
even stop after like looking into 17
chips so 17 is the most random number
between 1 and 20 you can you can look
that up on the Internet there's multiple
studies that confirm 17 is the most
random number so I didn't measure more
devices than 17 and also that was um one
of the mottos for um the Easter hack um
some years ago in Frankfurt so just 17
is the most random one that's
why um and then something funny happened
because um broadcom's customer who who
had this issue with the missing uh
Hardware random Jama generator got a bit
nervous and so they asked like can we
take wcom because um like maybe
somewhere else there's also um
Randomness
missing and then I said well I mean you
can tell them but at least we don't have
any NDA or something so they wouldn't
tell us and why should they tell you if
they are insecure so it really doesn't
make that much sense but of course you
can ask like if this black box of magic
of random number generator for qu chips
is uh is like broken and then they asked
and then they gave us some answer and
this answer I'm not allowed to show you
here and then I they gave me another
answer and that's the answer that I'm
allowed to show you here which is uh
yeah they didn't found any
indicators um that that they have the
same issue in uh a random number
generator or something so they say we
think our random numbers are secure um
but that's again thing so you you would
never ever know for a Bluetooth chip
until you do this whole reverse
engineering and all those measurements
if it is really
secure um now the impact so I said um in
all versions so or variant so variant
one to uh five the uh function RBG run
is called the same way um and that means
that there is one variant where it's put
into a wrapper so this sh get 128 byte
rent uh bit rent so this one is a 16
byte uh output and it's just taking 16
times the ivg Rand function and putting
it into the Sha function but it's just
in in a loop so that means that there is
not that much Randomness so for the
timers and so on um You can predict how
they change um and then also those those
values um that come from the signals
stay very similar over time so probably
it's just the same value over the whole
round um and then there's the other
variant so the red one above which is
ulp run this is ultra low power and it's
used for everything that's Bluetooth LE
and for those they are just copying
those four bytes as they are uh without
any sh on top um and you get the direct
state of the previous random value and
this is for example used in the um
security manager ulp function to uh to
send an initialization vector and this
one is to send in PL text over the air
before encryption starts for example so
this dat definitely
leaks um yeah so um random numbers are
needed for example in the numeric
comparison protocol that's a protocol
when you pair two devices and get a six
uh digit number shown on those devices
and this protocol prevents active man in
Middle attacks by making a commitment on
a random number um and then later
opening this commitment so a commitment
is just something I I give you a key for
a safe and I tell you in the save is
something and uh later I give you uh the
other way around I'll give you the the
save whatever but it's basically I'm
committing to something without telling
you the what and then later I open it
and this property breaks as soon as you
can predict the random number um so the
numeric comparison for demand and middle
attack um
is now vulnerable in that sense um yeah
and there is also a few other things
that break but this is just an example
so you can no longer do the pairing with
the six digigit number without being uh
secure against men and middle
attacks and then I looked into Android
and Android uh well they they had a good
idea so overall so if the Bluetooth chip
is um fips compliant it means um
sorry so if the if the um chip is so if
the RG is fips compliant it means that
the Bluetooth chip on an Android device
is a safe source of Randomness in that
sense so it's really good to take this
one because it's certified and Android
runs on very many many many many devices
and you never know if in a cheap
whatsoever uh China phone you would have
um a good RNG and it's a good idea to
take the Bluetooth
random uh yeah so that's why they do
this I think and what you can see in
this fire shark Trace is that the Le run
function which directly calls the ulp
run which directly calls the RBG run is
called multiple times in a row and the
first four calls are actually used to
create um an elliptic Cur def Helman
private key and then later compute a
public key and the second one is then
sent over the air
um and you you can also look this up in
the in the current Android code and this
of course means that well if you if you
have um RNG that is broken then the the
private Keys directly initialized with
with this one and so it's uh just
leaking the key without even any active
man in the middle so just a passive man
in the middle that somehow can infer
from the other numbers that are sent
over the air what what was the previous
state of the r is now able to know the
key just
passive now the question is so when will
there be a patch so the device uh with
the missing hardw random number
generator um I I skipped the name of the
device on purpose uh because this one
didn't um pass the 90day deadline yet
because we found this one a bit later um
but um the problem is that also broadcom
and their customer they cannot provide
us with um the patch in advance or they
don't even give us the binary or
something thing and they also don't tell
us when exactly it will be patched so
all I do is I go like to two vendor
websites and check like is there any
update announc and once there is the cve
that I initially um got from from Mitra
if this one is listed there then I can
hope for like uh yeah I don't know
reverse engineering that patch and if
it's not mentioned then usually it means
that there is no patch so I don't know
for the for the first issue that that
was really serious that we found I
started like um reverse engineering each
monthly patch and then like so I did it
for three months and it didn't happen
until in the fourth month it it was
happening and then it was already off
officially announced um and as there is
currently no patch announced um they
will definitely not make the 90-day
deadline and I also think like even if
giving them two more weeks it it really
will not make the deadline so um yeah
let's let's see how that develops but I
think there will not be any good patch
in
time so um the lesson learned don't
trust any embedded random number
generator or it might just be a bad P
random number generator that still was
passing some statistical tests um but
once you know the the inputs of such a p
random number generator uh you might see
that it's insecure so yeah you never you
never know um and then also during all
this patching I I really saw like how
the film evolved over more than 10 years
and how each of them has like their
individual bugs that you need to fix to
interact with it and to get like one
gigabyte out of data out of that chip
and so on and so forth so that was
definitely interesting uh for this
project and now I need to give some
credits first of all to Mara for
surviving AIS with me and um also Felix
who helps me with everything that's
crypto and that I don't understand then
there is Matias my boss uh who makes it
possible to buy like one smartphone and
another smartphone and I don't know and
another smartphone and still another
smartphone and then there is Jacob who
made it possible for me to access one of
the devices that I needed um remote in a
setup so he's also in the next mon team
and then I had two proof readers for the
paper that I wrote In Parallel um who
also helped me a lot like last minute
that's that's always the thing because
papers always get done last
minute um so that's it uh for my talk
and now you can ask questions um there's
also a pet where you can put in your
questions um and then I will answer
them so let's
see
a full screen for
my wait a second yep
um so do you see me full screen on my
camera
now I hope so I hope so okay um so the
questions um the first the
first what yeah yeah yeah yeah you can
only hear me in the live stream that's
okay oh I'm I'm I'm already in the
question pad so I I just answer the
question from the
pet
okay I can yeah so I can hear everyone
speaking the Mumble it's just that
people cannot hear me speaking the
Mumble but I can hear
you so
yeah
yeah yeah
okay yeah it it doesn't matter so I I
just I just read the questions myself
and answer the questions myself yeah
yeah yeah it's it's easier if I just do
it on my own I'm sorry um so the the
first question is if we are able to
access the main CPU from an exploit in
the Bluetooth chip so that that depends
so it's it's a complicated question
which I which I cannot fully answer yet
but
um
so okay so I'm going on my own so anyway
so there is uh so people are asking if
there is an exploit to um escalate into
the operating system um and so the first
thing is that there is like a lot of
drivers and I would say the most
interesting one is um since the iPhone
Xs and iPhone 11 they are attaching the
Bluetooth chip via PCI Express but
except from that I'm not
um uh commenting
anymore uh yeah so then people are
asking entropy yeah so I mean it's not
really random there's the timer which is
not random and then there's like um two
more inputs that are like one bite or
something but not even the full bite
being used so I don't know there might
be um like one bite or something that
you need to Pro Force
um uh yeah so next question how did we
access the Bluetooth chip on the iPhones
um yeah jailbreaks so um internal blue
is working well on everything like I
don't know I also have this this uh cute
iPhone uh six here um so on iPhone uh 6
on iOS 12 but also iOS 13 everything
that's an UI chip um it's working with
internal blue but you need a CH break
but yeah Checkmate does a great job and
then you can just install it
um yeah
so and
um no no no no in internal blue internal
blue someone
is ah can I I cannot edit the pet but
internal blue um and then
um it doesn't have anything to do with
the RKA up for the covid-19 tracking no
no no it's
nothing um we don't have any working
exploit right now I mean that that would
be cool like I don't know building
something to calculate it back yeah
um but then again um currently
publishing exploit is so so because it's
not being fixed in time so uh yeah I
mean we we probably should build it uh
it shouldn't be too highight based on
the
measurements
um uh yeah so then there is the next
question so how much uh money would
vendor save by not including uh a good
Hardware in I mean they just need to
include a good p random number generator
actually so uh that's everything that
the Bluetooth specification
requires um and I'm I'm not even sure
like um so for me for me the firm very
but I don't know it it might just be
that for the smartphone where it's
missing that they already put it in
there uh but didn't really VI it or
something or for example that um the
chip already went into production but I
don't think that they initially leave it
out to save some money
um yeah so next question
um so how can we make more accurate
statistical tests I mean die harder um
and so on they already have accurate
statistical tests um the problem is just
that if you have like some super random
number generator and don't know the
inputs then it will look very random
despite the input itself was not
random um yeah so the Pay-Per-View we
just submitted it to a conference um we
might so the conference doesn't prevent
us from from uh publishing on archive or
something um But it includes the model
of the vulnerable smartphone so we can
earliest we can do it would be I think
first of May or something so um
yeah then next comment is uh great work
and what does my unicorn think about all
the stuff I don't know so yeah unicorn
uh on the stream again saying hello
um yeah next
question um
if
um so how they how they could fix the
super random number generator using the
other sources than they had I I really I
really don't know and that's the thing
so that's why I asked them like how are
you going to fix this and they just said
like we are going to fix it in time and
this is this is really an issue the
whole the whole patching policy there um
so it's it's really annoying because I I
don't know how it how it will be fixed
and when it will be fixed so I have no
idea um and now yeah can I quickly
explain what random only memory is so
this is um basically just a joke that
Yan um is going to to make in
a so he's going to make the next talk so
and so I was like you know they don't
have a hardware random number generator
what do you think where they will like
get the randomness from when they patch
it and then I was like I don't know yeah
so maybe random access memory and then
just for fun we said like oh maybe
there's there's also uh random only
memory like ROM but ROM obviously is not
random only memory but it's just like
where the hell should they get the
sources from to make a good uh patch for
this uh yeah so why is there no SPF
record for bluetooth. law this this the
bluetooth. law domain I don't don't know
so for some Legacy reasons I I still
have some website hosted at one and one
or I don't know it's no United internet
or ionos I don't know what I just I just
clicked it there and there is nothing
properly configured on it I'm
sorry um and then last question why does
unicorn wear an antenna on its head yeah
so that's that's a controversial thing
like if tin foil heads actually uh help
you to um get less radiation or if they
increase uh
radiation uh yeah so I don't know but I
mean I it looks at least stylish I guess
um so enjoy it enjoy the the Hat um yeah
so I don't know so now you can probably
see it better that's that's the awesome
tinfoil head that my friends made for my
unicorn when it
graduated
um okay so I think that's the questions
already uh yeah cool no more questions I
guess except from if I hear something in
the Mumble but looks all right um so we
can probably hand over to
Yan