<s>
Proof-of-stake	B-Protocol
(	O
PoS	O
)	O
protocols	O
are	O
a	O
class	O
of	O
consensus	B-Operating_System
mechanisms	I-Operating_System
for	O
blockchains	B-Application
that	O
work	O
by	O
selecting	O
validators	O
in	O
proportion	O
to	O
their	O
quantity	O
of	O
holdings	O
in	O
the	O
associated	O
cryptocurrency	O
.	O
</s>
<s>
The	O
first	O
functioning	O
use	O
of	O
PoS	O
for	O
cryptocurrency	O
was	O
Peercoin	B-Protocol
in	O
2012	O
,	O
although	O
the	O
scheme	O
,	O
on	O
the	O
surface	O
,	O
still	O
resembled	O
a	O
POW	O
.	O
</s>
<s>
For	O
a	O
blockchain	B-Application
transaction	O
to	O
be	O
recognized	O
,	O
it	O
must	O
be	O
appended	O
to	O
the	O
blockchain	B-Application
.	O
</s>
<s>
In	O
the	O
proof	B-Protocol
of	I-Protocol
stake	I-Protocol
blockchain	B-Application
the	O
appending	O
entities	O
are	O
named	O
minters	O
or	O
(	O
in	O
the	O
proof	O
of	O
work	O
blockchains	B-Application
this	O
task	O
is	O
carried	O
out	O
by	O
the	O
miners	O
)	O
;	O
in	O
most	O
protocols	O
,	O
the	O
validators	O
receive	O
a	O
reward	O
for	O
doing	O
so	O
.	O
</s>
<s>
For	O
the	O
blockchain	B-Application
to	O
remain	O
secure	O
,	O
it	O
must	O
have	O
a	O
mechanism	O
to	O
prevent	O
a	O
malicious	O
user	O
or	O
group	O
from	O
taking	O
over	O
a	O
majority	O
of	O
validation	O
.	O
</s>
<s>
PoS	O
accomplishes	O
this	O
by	O
requiring	O
that	O
validators	O
have	O
some	O
quantity	O
of	O
blockchain	B-Application
tokens	O
,	O
requiring	O
potential	O
attackers	O
to	O
acquire	O
a	O
large	O
fraction	O
of	O
the	O
tokens	O
on	O
the	O
blockchain	B-Application
to	O
mount	O
an	O
attack	O
.	O
</s>
<s>
Proof	O
of	O
work	O
(	O
PoW	O
)	O
,	O
another	O
commonly	O
used	O
consensus	B-Operating_System
mechanism	I-Operating_System
,	O
uses	O
a	O
validation	O
of	O
computational	O
prowess	O
to	O
verify	O
transactions	O
,	O
requiring	O
a	O
potential	O
attacker	O
to	O
acquire	O
a	O
large	O
fraction	O
of	O
the	O
computational	O
power	O
of	O
the	O
validator	O
network	O
.	O
</s>
<s>
delegated	O
proof	B-Protocol
of	I-Protocol
stake	I-Protocol
(	O
DPoS	O
)	O
;	O
</s>
<s>
liquid	O
proof	B-Protocol
of	I-Protocol
stake	I-Protocol
(	O
LPoS	O
)	O
.	O
</s>
<s>
The	O
additional	O
vulnerabilities	O
of	O
the	O
PoS	O
schemes	O
are	O
directly	O
related	O
to	O
their	O
advantage	O
,	O
a	O
relatively	O
low	O
amount	O
of	O
calculations	O
to	O
be	O
performed	O
while	O
constructing	O
a	O
blockchain	B-Application
.	O
</s>
<s>
The	O
low	O
amount	O
of	O
computing	O
power	O
involved	O
allows	O
a	O
class	O
of	O
attacks	O
that	O
replace	O
a	O
non-negligible	O
portion	O
of	O
the	O
main	O
blockchain	B-Application
with	O
a	O
hijacked	O
version	O
.	O
</s>
<s>
The	O
early	O
stages	O
of	O
a	O
blockchain	B-Application
are	O
much	O
more	O
malleable	O
for	O
rewriting	O
,	O
as	O
they	O
likely	O
have	O
much	O
smaller	O
group	O
of	O
stakeholders	O
involved	O
,	O
simplifying	O
the	O
collusion	O
.	O
</s>
<s>
The	O
PoS	O
schemes	O
enable	O
low-cost	O
creation	O
of	O
blockchain	B-Application
alternatives	O
starting	O
at	O
any	O
point	O
in	O
history	O
(	O
costless	O
simulation	O
)	O
,	O
submitting	O
these	O
forks	O
to	O
eager	O
validators	O
endangers	O
the	O
stability	O
of	O
the	O
system	O
.	O
</s>
<s>
If	O
this	O
situation	O
persists	O
,	O
it	O
can	O
allow	O
double-spending	B-Operating_System
,	O
where	O
a	O
digital	O
token	O
can	O
be	O
spent	O
more	O
than	O
once	O
.	O
</s>
<s>
Bribery	O
attack	O
,	O
where	O
the	O
attackers	O
financially	O
induce	O
some	O
validators	O
to	O
approve	O
their	O
fork	O
of	O
blockchain	B-Application
,	O
is	O
enhanced	O
in	O
PoS	O
,	O
as	O
rewriting	O
a	O
large	O
portion	O
of	O
history	O
might	O
enable	O
the	O
collusion	O
of	O
once-rich	O
stakeholders	O
that	O
no	O
longer	O
hold	O
significant	O
amounts	O
at	O
stake	O
to	O
claim	O
a	O
necessary	O
majority	O
at	O
some	O
point	O
back	O
in	O
time	O
,	O
and	O
grow	O
the	O
alternative	O
blockchain	B-Application
from	O
there	O
,	O
an	O
operation	O
made	O
possible	O
by	O
the	O
low	O
computing	O
cost	O
of	O
adding	O
blocks	O
in	O
the	O
PoS	O
scheme	O
.	O
</s>
<s>
NPoS	O
is	O
utilized	O
by	O
Ouroboros	B-General_Concept
Praos	I-General_Concept
and	O
BABE	O
.	O
</s>
<s>
Proof	B-Protocol
of	I-Protocol
stake	I-Protocol
delegated	O
systems	O
use	O
a	O
two-stage	O
process	O
:	O
first	O
,	O
</s>
<s>
LPoS	O
is	O
used	O
in	O
Tezos	B-Protocol
.	O
</s>
<s>
The	O
first	O
functioning	O
implementation	O
of	O
a	O
proof-of-stake	B-Protocol
cryptocurrency	O
was	O
Peercoin	B-Protocol
,	O
introduced	O
in	O
2012	O
.	O
</s>
<s>
Other	O
cryptocurrencies	O
,	O
such	O
as	O
Blackcoin	O
,	O
Nxt	B-Application
,	O
Cardano	B-Protocol
,	O
and	O
Algorand	O
followed	O
.	O
</s>
<s>
In	O
September	O
2022	O
,	O
Ethereum	B-Application
,	O
the	O
world	O
second	O
largest	O
cryptocurrency	O
in	O
2022	O
,	O
switched	O
from	O
proof	O
of	O
work	O
to	O
a	O
proof	B-Protocol
of	I-Protocol
stake	I-Protocol
consensus	B-Operating_System
mechanism	I-Operating_System
system	O
,	O
after	O
several	O
proposals	O
and	O
some	O
delays	O
.	O
</s>
<s>
Critics	O
have	O
argued	O
that	O
the	O
proof	B-Protocol
of	I-Protocol
stake	I-Protocol
model	O
is	O
less	O
secure	O
compared	O
to	O
the	O
proof	O
of	O
work	O
model	O
.	O
</s>
<s>
Critics	O
have	O
argued	O
that	O
the	O
proof	B-Protocol
of	I-Protocol
stake	I-Protocol
will	O
likely	O
lead	O
cryptocurrency	O
blockchains	B-Application
being	O
more	O
centralized	O
in	O
comparison	O
to	O
proof	O
of	O
work	O
as	O
the	O
system	O
favors	O
users	O
who	O
have	O
a	O
large	O
amount	O
of	O
cryptocurrency	O
,	O
which	O
in	O
turn	O
could	O
lead	O
to	O
users	O
who	O
have	O
a	O
large	O
amount	O
of	O
cryptocurrency	O
having	O
major	O
influence	O
on	O
the	O
management	O
and	O
direction	O
for	O
a	O
crypto	O
blockchain	B-Application
.	O
</s>
<s>
In	O
2021	O
a	O
study	O
by	O
the	O
University	O
of	O
London	O
found	O
that	O
in	O
general	O
the	O
energy	O
consumption	O
of	O
the	O
proof-of-work	O
based	O
Bitcoin	B-Protocol
was	O
about	O
a	O
thousand	O
times	O
higher	O
than	O
that	O
of	O
the	O
highest	O
consuming	O
proof-of-stake	B-Protocol
system	O
that	O
was	O
studied	O
even	O
under	O
the	O
most	O
favorable	O
conditions	O
and	O
that	O
most	O
proof	B-Protocol
of	I-Protocol
stake	I-Protocol
systems	O
cause	O
less	O
energy	O
consumption	O
in	O
most	O
configurations	O
.	O
</s>
<s>
The	O
researchers	O
also	O
noted	O
that	O
the	O
energy	O
consumption	O
for	O
proof-of-stake	B-Protocol
with	O
permissioned	O
systems	O
that	O
used	O
less	O
validators	O
were	O
more	O
efficient	O
than	O
permission-less	O
systems	O
that	O
do	O
n't	O
use	O
validators	O
at	O
all	O
.	O
</s>
<s>
They	O
also	O
could	O
n't	O
find	O
the	O
energy	O
consumption	O
of	O
a	O
proof-of-stake	B-Protocol
system	O
on	O
a	O
large	O
scale	O
,	O
as	O
such	O
a	O
system	O
did	O
not	O
exist	O
at	O
the	O
time	O
of	O
the	O
report	O
.	O
</s>
<s>
In	O
January	O
2022	O
Vice-Chair	O
of	O
the	O
European	O
Securities	O
and	O
Markets	O
Authority	O
Erik	O
Thedéen	O
called	O
on	O
the	O
EU	O
to	O
ban	O
the	O
proof	O
of	O
work	O
model	O
in	O
favor	O
of	O
the	O
proof	B-Protocol
of	I-Protocol
stake	I-Protocol
model	O
due	O
to	O
its	O
lower	O
energy	O
consumption	O
.	O
</s>
<s>
On	O
15	O
September	O
2022	O
,	O
Ethereum	B-Application
transitioned	O
its	O
consensus	B-Operating_System
mechanism	I-Operating_System
from	O
proof-of-work	O
to	O
proof-of-stake	B-Protocol
in	O
an	O
upgrade	O
process	O
known	O
as	O
"	O
the	O
Merge	O
"	O
.	O
</s>
<s>
This	O
has	O
cut	O
Ethereum	B-Application
's	O
energy	O
usage	O
by	O
99%	O
.	O
</s>
