so um as mentioned my name is Haroon and
i was speaking about how we trace
transactions that went across cryptic
cartilages this work is done by myself
George Capas and Sarah Mahajan all of
our from University College on so as
obviously we speak about printer
currencies we shall first start with
Bitcoin
so Bitcoin was at many as they said many
times before the first winter coffee
that was created in 2009 12 2008 she
then first you did 2009 waited by one of
the synonymous author Satoshi Nakamoto
now with the system he was designed with
the issue of having pseudonymity without
by users who transact with each other
have addresses which are unique and with
that add a layer of anonymity but within
this year they also mentioned that there
are some issues with the system first
being that's only anonymous if you keep
your your coin your addresses private
and the second is that if you leak your
key then the transactions I have leaked
can be perhaps been linked towards you
and for them going backwards and going
forwards but what they also don't
mention is that if you were to other
people were to leak your information
would leak their information that could
then also be used to target you so
they're not more than five years later
we see a large plethora of research
which looks at attacking back when I
mean of MTI provides many of these of
these systems use techniques like
address tracking address tagging and
also address clustering in order to
identify the antecedent system how they
interact with each other and the overall
flow as well as this we've also seen
many crimes that no Bitcoin which then
used these techniques in order to
determine where the coins when and how
and if they can't float the crimean
process or the one of the most famous
ones was the amount GOx hack which the
very was the biggest exchange back in
the day for tea they were hired to lost
many of their coins but but using these
tracking techniques will be able to find
that these coins actually went to
another exchange
very recently another exchange balance
was hacked and they they eight million
dollars worth of bitcoins was stolen
these are however been
very closely monitors in case say what
to move to an exchange with it could be
prison Bitcoin isn't the only kind of
currency as you honor there are many
others in the space um there are some
privacy once was almost the cash and
Monaro a Volusia use next and the
privacy audiology symposium they were
attacked sour the that were shown upon
these to anonymity wait so I'm trying to
say here that the attacks are not only
supposed to pick one they're also
specific to anonymity coins now all of
these systems alone these attacks occur
on unchanged that occur within the same
ecosystem
well the Bitcoin attacks occur in a
Bitcoin or the Zika attacks occur within
Z cash so that's one change seems to be
very studied and very looked into your
amigo system but we've also seen a trend
of crime going across chain this is
where users move their coins from Bix a
Bitcoin and they're backed by a theory
when the most famous ones ones happen
recently was the one a crack attack
which was a ransom which affected many
hospitals and a do so they were able to
get one hundred forty two thousand
dollars worth of Bitcoin which they then
laundered through cross currency
exchanges so the question now is can we
track exchanges that allow you to do
cross currency trades so there are a
couple of exchanges which do this two of
which we will speak about shape-shift
and change Li focusing mainly on
shape-shift what the doggies are
exchange try to do cross currently
trades so they're like a lightweight
exchange they allow user to exchange
multiple coins you're gonna shake bacon
for a 30 mm for bicker whatever point
you have and well the coins support you
can crush it over in currently custom we
have arrived 2000 cryptocurrencies but
they combine the right to convert over
140 so why would you do cross trade war
there's many reasons that I said before
it's very easy to use which I'll
demonstrate perhaps give us some
protection and Amity which won't explain
they're not custodial and that means
that you don't need them like you
already need to have your coins in or
account you just go to the website do
the trade
you've got your pointer back are
straight away and also simply cheaper
because you also do a single rate of
change so how do you do a shift with is
very very straightforward you go to a
website and you say yeah I got Bitcoin
and I want to get some thorough
the next thing you do is you then say
okay I've got this is the ones I want to
confirm you give them the address that
you want your coins to be sent to it's
not a case we want to give them an
ethereal address because we want to get
thrown from our trade after that we then
send them a bit quick to adjust that
they specify once they confirm their
bitcoins and they validate transaction
they then will give us an alluring and
that's it the trade is completely done
you're not gonna cross a cross chain so
what this looks like here on the tube
block changes we've got a queen a which
you're not kiss was Bitcoin and calling
B which you can say is the transaction
flows of ethereum now in point a we said
that we've gone from our case to perhaps
of shifting service that we might know
the address of but in coin B we don't
know where that changes and with that
trades and a dot which no did a go -
hardly propagate afterwards so the aim
of our research is to indeed find the
link which can allow you to connect the
currency which go across chain these are
some of the contributions that we did in
our paper now go through most of them as
we progress through this talk the first
one being the analysis that we did and
how we obtain the data set in order to
perform our attacks of course to do to
do this attack you first need data and
there was a sensor one much it available
we're gonna get ourselves do this so for
this we just went to the urology see at
the bottom and we scraped they can't the
API for a number of month for 30 months
no to obtain a large mass of
transactions well this will give you is
the following you've got a very simple
JSON which contains full acidic piece of
information the currency inputs are the
personal carts you want to send the
output point to the person the currency
that they wanted
you've got the amount that had sent and
you've also got the timestamp with these
simple things we cannot figure out what
was the transaction the person did on
the first chain so in our case just with
Bitcoin so we know we've got Bitcoin
which is fine here we know we've got a
value of zero point five one and lots of
other digits so we go and chain can we
find a transaction with this specific
output value and this specific time give
or take some blocks was on Bitcoin and
in fact we
did fine and this is an example
transaction that editor now we have this
transaction what do we get we got the
user who did the exchange we also have
the exchange shape-shift which was
platform the use used now funny of this
the shape-shift exchange actually allow
actual give you information about the
exchange done if you give them an
address let's say this address able to
use a seconds to you they will then tell
you if this is correct and if it was
quite that will return the full
transaction that happened so here we see
the user got Bitcoin cash here 2.7
Bitcoin caches and the transaction hash
that was available I'm just going to
blockchain check this if this is real if
this is real we now have the full data
of the exchange and the user and when
they receive the money that's just a
very simple three-step process Script
API find the transaction and then look
at the look again Ali p8 confirm this is
correct although there are ways to do
this without using the API but you can
read that in the paper so now we just
shown you is how to link currencies and
exchanges that go across chain I mean I
found the link and we found the shift
that's to call it so now we know how to
do how to do this attack
we looked into some of the heuristics
that we could understand to figure out
how users interact
of course we first offer some results we
scripted for 13 months so this as I said
you've got two point eight million
shifts in total and from need to pick
top eight coins which are around 2.3
million transact
transactions to do this we also have to
go into that run a full node download
all the data and then pass all the data
in order to be able to look into the
chains ourselves so how do we do so
before we were able to try 1.3 million
transactions that weren't completely
cross chain but give us the input
transaction and the upper transaction
duck and so the best case for Z cash we
obtained run 90% of who those
transactions for the worst case which is
Bitcoin we obtain 76% so we now we know
how to go through the chain what about
what bars people try to be clever why
they try to you know move their coins
around try to be small try to obscure
what they're doing so that we came up
with two extra heuristics the first one
was called a u-turn now
it's very straightforward as you see in
the picture the two shifts which are
very close in time and proximity the
first case said the person fix something
he can't they have Bitcoin they do one
trade and they go to Z cash after some
time they wait maybe like half an hour
etc then then do another shift and they
go back into Bitcoin question is how
many users did this kind of transaction
and of these can we figure out the
values all if they had perhaps you the
same coins I've gone using different
addresses and then what this allows us
to do is figure out the movement of
coins wants to use a cell money to the
exchange what did they do then after
that so we found over one hundred and
seven thousand transactions which
matched our heuristic of these we found
ten thousand with a person whose exact
same address that they had received quiz
from I was so and of these these a
thousand of them actually the exact same
coins meaning they did a complete trade
going full circle so another case is
round trip what if a use used it went
through the circle but in fact he did
something in the bottom here between the
trade was kind of obscured what he was
up to you so that is bracing to the
u-turn is two shifts both in close time
and in close value well we're looking
how here is if the first if the value of
the first shift is similar to the value
of the second shift or if they return to
the exact same input address did this
user go from Bitcoin to Z cash do
something that we weren't sure of and
then go all the way back through back to
the original dress and the advantage
over the original one here is that the
identity of the person of the original
initiator is actually known because you
know this person did a Bitcoin
transaction here and he did something
and then he went through Z cash back
again to his version address now from
from that we find around a hot 10,000
100,000
transactions which which one where is
your stake and of those 10,000 actually
went full circle and use the same
address so this another reason is the
point is because it helps us to identify
users who perhaps used the cross chain
system as a way to mix their coins
around and attempt to obscure the
transaction
so now you know how work you know some
of the attacks that we did also look
into some real world scams or a real
world scam where someone in fact did use
this question you know to get away with
the crime so um Russia in lost year late
in early January the fan came up caught
starscape capital what they promise is
that if you invest in our fund who in
fact give you a guaranteed 50% return
and our special trading boat which does
lots of magic machine learning and
generates a big income blow up or okay
obviously this is a good deal they look
like legit company let's give them money
and so they did and they raised their on
two point two million dollars in Gerry
2018 then of course you know you can't
even get 50 percent of stock market so
this is of course a scam and soon off
the disappeared the removed got rid of
the coins and moved it to a different
address they moved the website the
Ramudu social media they had completely
gone off the grid but by looking to a
more into more detail using the
techniques we showed before we
identified that they actually a quarter
of their theory and they shifted
straight into manera because from that
they it can email it to my burner
addresses that received these coins so
there are more scammed in the people
which you can look into such as many
scams on ethereum DB which actually go
question but I will leave that out for
the talk when the last time things we
looked into is how it uses make use of
privacy coins you do they use proper
sequence you know to augment the fact
that they can do a crushing so for this
we use two currencies which we know very
well with the first ones that see cash
and the second one was - so Z cash you
have this feature called the shielded
pool and where does it you put your
coins into the pool and then it become
completely hidden or on the chain you
can move senator on the user you can
split your Queen and do everyone but
they will be the addresses and the
values that you thought would be
completely hidden so okay for in Z cash
how many people send money from the pool
directed to this crushed in exchange
this would mean the exchange refused
coins from a place it cannot
legitimately identify this an unknown
area from that we found our 3800 turns
action which is quite significant which
Kim which are today's money is there are
three quarters of a million dollars
worth of coins
another case we looked into was - sure -
and I shouldn't do something called Co
enjoyed when you makes your transaction
with many other people and doing so you
try to hide who you are sending your
Queens to fourth man - all the inputs
that you do are similar to the same -
the outputs it makes it very very
difficult to determine who had sent
coins to whom that we thought okay how
many people do a quaint join and of
those how many then send them money to
shape-shift from this we found our two
thousand transactions of those one point
of the value is currently 1.2 million
dollars worth this may seem seem like to
be significant Oh - of the volume of
both of these coins over this issue
doesn't agree we don't find that this
kind of music doesn't provide anonymity
it specifically in these two points we
have to go back and use our u-turn here
so you figure out how people in these
ecosystems
use their addresses on the coins
fortunately people in - it seems to use
the same address quite or not and in
fact with an R you tell you find it was
a 64% of them if I use the same address
and easy cash we found that those who
had done a u-turn 54% of them use the
same address and of this 28% of them
actually use exact same coin you mean
the dinner obviously obviously obtain
any anonymity from using these two
systems the reason for that are clear
paps they don't know to use the system
or perhaps they just weren't sure what
what was happening
perhaps today I want an M and an empty
in the first place the summary these
were our contributions we looked into
transaction of cross chain some of our
heuristics there's a relationship
heuristic which you can look into in a
paper which shows you how entities
within the cross unique system operate
and who are the big plays they're looked
into some real-world scams are also more
in the paper we also looked into how
people trade within the system and if
any of them you for transactions protect
your obtain money i'm chris from
arbitrage all other ways to obtain
profit I will also show some demos and
how people who use privacy queens
interact with a cross chain system for
that I am nothing thanks
[Applause]
as you have questions we go for lunch
hey Dave great talk
artemiy from the University of British
Columbia I have a question for example
if you have you consider or have you
seen transactions where they possibly
change let's say Theory m2 Bitcoin and
Dan used tumbling services or other
privacy-preserving techniques so we we
didn't actually look into whether or not
they use mixing surface often but I mean
we have data so there's no reason why
people couldn't have this there's no
reason that prevents this from happening
I did a shirt people did use obtain
Quinn from like for example using Susie
from Zeke I should then from them they
didn't move their money into the pool
this is in the paper people did obtain
went from shape-shift and then do a coat
went straight after but I we found will
be significantly lower all right thanks
so much
okay any other questions for her own
yeah one thing I didn't quite understand
is with Z cache as I understand the
addresses and values are concealed how
did you know the total amount and volume
that was being transferred into these
services so Z cache in fact multiple
types of transactions you can do within
the pool one of them is a very private
one which you can't reduce doesn't or
anything which exchange does not allow
you to do but it doesn't like to do an
extra additional transaction where you
go from the pool into the exchange when
you do this you do not reveal who you
are but you do reveal how many coins you
send and then from W able to type and
tally the total amounts thank you yeah
okay so you have a brief question that
you're the way you find transactions
realize and timing and on values so what
would be a good attack against your
approach if the attackers willing to get
smarter could could they split this over
multiple smaller transactions or wait
you know longer time in order to do the
transfers so there are few ways you can
through when we've done one of them is
students not review the transactions
like the the exchange is very very
transparent just one of the big
advantages if they didn't do this and be
very difficult to track setting up the
second way would be to just look into
how the blockchain operates I try to
mimic other users like this a lot of
people like for example a Bitcoin we
when we found out that there are much
lower accuracy in determining the
transaction but this is because beacon
at such a high throughput that's a lot
people do those values it's hard to
figure out who was who so they were to
try make that they could obtain more
privacy but the issue then last one was
a very advanced users will they have
time to be able to look into this and is
it worth the effort to do so okay let's
take call our speakers and
you