<s>
Zerocoin	B-Protocol
is	O
a	O
privacy	O
protocol	O
proposed	O
in	O
2013	O
by	O
Johns	O
Hopkins	O
University	O
professor	O
Matthew	O
D	O
.	O
Green	O
and	O
his	O
graduate	O
students	O
,	O
Ian	O
Miers	O
and	O
Christina	O
Garman	O
.	O
</s>
<s>
It	O
was	O
designed	O
as	O
an	O
extension	O
to	O
the	B-General_Concept
Bitcoin	I-General_Concept
protocol	I-General_Concept
that	O
would	O
improve	O
Bitcoin	B-General_Concept
transactions	O
 '	O
anonymity	O
by	O
having	O
coin-mixing	O
capabilities	O
natively	O
built	O
into	O
the	O
protocol	O
.	O
</s>
<s>
Zerocoin	B-Protocol
is	O
not	O
currently	O
compatible	O
with	O
Bitcoin	B-General_Concept
.	O
</s>
<s>
Due	O
to	O
the	O
public	O
nature	O
of	O
the	O
blockchain	B-Application
,	O
users	O
may	O
have	O
their	O
privacy	O
compromised	O
while	O
interacting	O
with	O
the	O
network	O
.	O
</s>
<s>
In	O
May	O
2013	O
,	O
Matthew	O
D	O
.	O
Green	O
and	O
his	O
graduate	O
students	O
(	O
Ian	O
Miers	O
and	O
Christina	O
Garman	O
)	O
proposed	O
the	O
Zerocoin	B-Protocol
protocol	I-Protocol
where	O
cryptocurrency	O
transactions	O
can	O
be	O
anonymized	O
without	O
going	O
through	O
a	O
trusted	O
third-party	O
,	O
by	O
which	O
a	O
coin	O
is	O
destroyed	O
then	O
minted	O
again	O
to	O
erase	O
its	O
history	O
.	O
</s>
<s>
Initially	O
,	O
the	O
Zerocoin	B-Protocol
protocol	I-Protocol
was	O
planned	O
to	O
be	O
integrated	O
into	O
the	O
Bitcoin	B-General_Concept
network	I-General_Concept
.	O
</s>
<s>
However	O
,	O
the	O
proposal	O
was	O
not	O
accepted	O
by	O
the	O
Bitcoin	B-General_Concept
community	O
.	O
</s>
<s>
Thus	O
,	O
the	O
Zerocoin	B-Protocol
developers	O
decided	O
to	O
launch	O
the	O
protocol	O
into	O
an	O
independent	O
cryptocurrency	O
.	O
</s>
<s>
The	O
project	O
to	O
create	O
a	O
standalone	O
cryptocurrency	O
implementing	O
the	O
Zerocoin	B-Protocol
protocol	I-Protocol
was	O
named	O
"	O
Moneta	O
"	O
.	O
</s>
<s>
In	O
September	O
2016	O
,	O
Zcoin	O
(	O
XZC	O
)	O
,	O
the	O
first	O
cryptocurrency	O
to	O
implement	O
the	O
zerocoin	B-Protocol
protocol	I-Protocol
,	O
was	O
launched	O
by	O
Poramin	O
Insom	O
and	O
team	O
.	O
</s>
<s>
In	O
January	O
2018	O
,	O
an	O
academic	O
paper	O
partially	O
funded	O
by	O
Zcoin	O
was	O
published	O
on	O
replacing	O
Proof-of-work	O
system	O
with	O
memory	O
intensive	O
Merkle	B-Algorithm
tree	I-Algorithm
proof	O
algorithm	O
in	O
ensuring	O
more	O
equitable	O
mining	O
among	O
ordinary	O
users	O
.	O
</s>
<s>
In	O
April	O
2018	O
,	O
a	O
cryptographic	O
flaw	O
was	O
found	O
in	O
the	O
Zerocoin	B-Protocol
protocol	I-Protocol
which	O
allows	O
an	O
attacker	O
to	O
destroy	O
the	O
coins	O
owned	O
by	O
honest	O
users	O
,	O
create	O
coins	O
out	O
of	O
thin	O
air	O
,	O
and	O
steal	O
users	O
 '	O
coins	O
.	O
</s>
<s>
In	O
December	O
2018	O
,	O
Zcoin	O
released	O
an	O
academic	O
paper	O
proposing	O
the	O
Lelantus	O
protocol	O
that	O
removes	O
the	O
need	O
for	O
a	O
trusted	O
setup	O
and	O
hides	O
the	O
origin	O
and	O
the	O
amount	O
of	O
coins	O
in	O
a	O
transaction	O
when	O
using	O
the	O
Zerocoin	B-Protocol
protocol	I-Protocol
.	O
</s>
<s>
Transactions	O
which	O
use	O
the	O
Zerocoin	B-Protocol
feature	O
are	O
drawn	O
from	O
an	O
escrow	O
pool	O
,	O
where	O
each	O
coin	O
's	O
transaction	O
history	O
is	O
erased	O
when	O
it	O
emerges	O
.	O
</s>
<s>
Transactions	O
are	O
verified	O
by	O
zero-knowledge	B-Protocol
proofs	I-Protocol
,	O
a	O
mathematical	O
way	O
to	O
prove	O
a	O
statement	O
is	O
true	O
without	O
revealing	O
any	O
other	O
details	O
about	O
the	O
question	O
.	O
</s>
<s>
On	O
16	O
November	O
2013	O
,	O
Matthew	O
D	O
.	O
Green	O
announced	O
the	O
Zerocash	B-Protocol
protocol	O
,	O
which	O
provides	O
additional	O
anonymity	O
by	O
shielding	O
the	O
amount	O
transacted	O
.	O
</s>
<s>
Zerocash	B-Protocol
reduces	O
transaction	O
sizes	O
by	O
98%	O
,	O
however	O
was	O
significantly	O
more	O
computationally	O
expensive	O
,	O
taking	O
up	O
to	O
3.2GB	O
of	O
memory	O
to	O
generate	O
.	O
</s>
<s>
Zerocash	B-Protocol
utilizes	O
succinct	O
non-interactive	O
zero-knowledge	B-Protocol
arguments	O
of	O
knowledge	O
(	O
also	O
known	O
as	O
zk-SNARKs	O
)	O
,	O
a	O
special	O
kind	O
of	O
zero-knowledge	B-Protocol
method	O
for	O
proving	O
the	O
integrity	O
of	O
computations	O
.	O
</s>
<s>
However	O
,	O
unlike	O
Zerocoin	B-Protocol
,	O
Zerocash	B-Protocol
requires	O
an	O
initial	O
set	O
up	O
by	O
a	O
trusted	O
entity	O
.	O
</s>
<s>
Developed	O
by	O
Matthew	O
D	O
.	O
Green	O
,	O
the	O
assistant	O
professor	O
behind	O
the	O
Zerocoin	B-Protocol
protocol	I-Protocol
,	O
Zcash	B-Protocol
was	O
the	O
first	O
Zerocash	B-Protocol
based	O
cryptocurrency	O
which	O
began	O
development	O
in	O
2013	O
.	O
</s>
<s>
In	O
the	O
late	O
2014	O
,	O
Poramin	O
Insom	O
,	O
a	O
student	O
in	O
Masters	O
in	O
Security	O
Informatics	O
from	O
Johns	O
Hopkins	O
University	O
wrote	O
a	O
paper	O
on	O
implementing	O
the	O
zerocoin	B-Protocol
protocol	I-Protocol
into	O
a	O
cryptocurrency	O
with	O
Matthew	O
Green	O
as	O
faculty	O
member	O
.	O
</s>
<s>
On	O
20	O
February	O
2017	O
,	O
a	O
malicious	O
coding	O
attack	O
on	O
Zerocoin	B-Protocol
protocol	I-Protocol
created	O
370,000	O
fake	O
tokens	O
which	O
perpetrators	O
sold	O
for	O
over	O
400	O
Bitcoins	B-General_Concept
( $	O
440,000	O
)	O
.	O
</s>
<s>
Zcoin	O
team	O
announced	O
that	O
a	O
single-symbol	O
error	O
in	O
a	O
piece	O
of	O
code	O
"	O
allowed	O
an	O
attacker	O
to	O
create	O
Zerocoin	B-Protocol
spend	O
transactions	O
without	O
a	O
corresponding	O
mint	O
"	O
.	O
</s>
<s>
Unlike	O
Ethereum	B-Application
during	O
the	O
DAO	O
event	O
,	O
developers	O
have	O
opted	O
not	O
to	O
destroy	O
any	O
coins	O
or	O
attempt	O
to	O
reverse	O
what	O
happened	O
with	O
the	O
newly	O
generated	O
ones	O
.	O
</s>
<s>
In	O
September	O
2018	O
,	O
Zcoin	O
introduced	O
the	O
Dandelion	O
protocol	O
that	O
hides	O
the	O
origin	O
IP	O
address	O
of	O
a	O
sender	O
without	O
using	O
a	O
The	B-Application
Onion	I-Application
Router	I-Application
(	O
Tor	B-Application
)	O
or	O
Virtual	B-Application
Private	I-Application
Network	I-Application
(	O
VPN	B-Application
)	O
.	O
</s>
<s>
In	O
November	O
2018	O
,	O
Zcoin	O
conducted	O
the	O
world	O
's	O
first	O
large-scale	O
party	O
elections	O
in	O
Thailand	O
Democrat	O
Party	O
using	O
InterPlanetary	B-Protocol
File	I-Protocol
System	I-Protocol
(	O
IPFS	B-Protocol
)	O
.	O
</s>
<s>
In	O
December	O
2018	O
,	O
Zcoin	O
implemented	O
Merkle	B-Algorithm
tree	I-Algorithm
proof	O
,	O
a	O
mining	O
algorithm	O
that	O
deters	O
the	O
usage	O
of	O
Application-specific	O
integrated	O
circuit	O
(	O
ASIC	O
)	O
in	O
mining	O
coins	O
by	O
being	O
more	O
memory	O
intensive	O
for	O
the	O
miners	O
.	O
</s>
<s>
This	O
allows	O
ordinary	O
users	O
to	O
use	O
central	B-General_Concept
processing	I-General_Concept
unit	I-General_Concept
(	O
CPU	O
)	O
and	O
graphics	B-Device
card	I-Device
for	O
mining	O
,	O
so	O
as	O
to	O
enable	O
egalitarianism	O
in	O
coin	O
mining	O
.	O
</s>
<s>
On	O
30	O
July	O
2019	O
,	O
Zcoin	O
formally	O
departed	O
from	O
Zerocoin	B-Protocol
protocol	I-Protocol
by	O
adopting	O
a	O
new	O
protocol	O
called	O
"	O
Sigma	O
"	O
that	O
prevents	O
counterfeit	O
privacy	O
coins	O
from	O
inflating	O
coin	O
supply	O
.	O
</s>
<s>
This	O
is	O
achieved	O
by	O
removing	O
a	O
feature	O
called	O
"	O
trusted	O
setup	O
"	O
from	O
the	O
Zerocoin	B-Protocol
protocol	I-Protocol
.	O
</s>
<s>
One	O
criticism	O
of	O
zerocoin	B-Protocol
is	O
the	O
added	O
computation	O
time	O
required	O
by	O
the	O
process	O
,	O
which	O
would	O
need	O
to	O
have	O
been	O
performed	O
primarily	O
by	O
bitcoin	B-General_Concept
miners	O
.	O
</s>
<s>
If	O
the	O
proofs	O
were	O
posted	O
to	O
the	O
blockchain	B-Application
,	O
this	O
would	O
also	O
dramatically	O
increase	O
the	O
size	O
of	O
the	O
blockchain	B-Application
.	O
</s>
<s>
Nevertheless	O
,	O
as	O
stated	O
by	O
the	O
original	O
author	O
,	O
the	O
proofs	O
could	O
be	O
stored	O
outside	O
the	O
blockchain	B-Application
.	O
</s>
<s>
Since	O
a	O
zerocoin	B-Protocol
will	O
have	O
the	O
same	O
denomination	O
as	O
the	O
bitcoin	B-General_Concept
used	O
to	O
mint	O
the	O
zerocoin	B-Protocol
,	O
anonymity	O
would	O
be	O
compromised	O
if	O
no	O
other	O
zerocoins	B-Protocol
(	O
or	O
few	O
zerocoins	B-Protocol
)	O
with	O
the	O
same	O
denomination	O
are	O
currently	O
minted	O
but	O
unspent	O
.	O
</s>
<s>
A	O
potential	O
solution	O
to	O
this	O
problem	O
would	O
be	O
to	O
only	O
allow	O
zerocoins	B-Protocol
of	O
specific	O
set	O
denominations	O
,	O
however	O
,	O
this	O
would	O
increase	O
the	O
needed	O
computation	O
time	O
since	O
multiple	O
zerocoins	B-Protocol
could	O
be	O
needed	O
for	O
one	O
transaction	O
.	O
</s>
<s>
Depending	O
on	O
the	O
specific	O
implementation	O
,	O
Zerocoin	B-Protocol
requires	O
two	O
very	O
large	O
prime	O
numbers	O
to	O
generate	O
a	O
parameter	O
which	O
cannot	O
be	O
easily	O
factored	O
.	O
</s>
<s>
Such	O
a	O
setup	O
,	O
however	O
,	O
is	O
not	O
possible	O
with	O
the	O
Zerocash	B-Protocol
protocol	O
.	O
</s>
