<s>
Ouroboros	B-General_Concept
is	O
a	O
family	O
of	O
proof-of-stake	B-Protocol
consensus	O
protocols	O
used	O
in	O
the	O
Cardano	B-Protocol
and	O
Polkadot	B-Protocol
blockchains	B-Application
.	O
</s>
<s>
It	O
can	O
run	O
both	O
permissionless	O
and	O
permissioned	O
blockchains	B-Application
.	O
</s>
<s>
Ouroboros	B-General_Concept
was	O
published	O
as	O
"	O
the	O
first	O
provable	O
secure	O
PoS	O
consensus	O
protocol	O
"	O
.	O
</s>
<s>
Later	O
that	O
year	O
,	O
Ouroboros	B-General_Concept
(	O
Classic	O
)	O
was	O
implemented	O
by	O
IOHK	O
as	O
the	O
basis	O
of	O
the	O
Cardano	B-Protocol
blockchain	B-Application
platform	O
and	O
various	O
upgrades	O
.	O
</s>
<s>
Ouroboros	B-General_Concept
versions	O
include	O
:	O
</s>
<s>
Ouroboros	B-General_Concept
BFT	O
was	O
an	O
interim	O
version	O
used	O
in	O
2020	O
to	O
enable	O
the	O
switch	O
between	O
the	O
Classic	O
and	O
Praos	O
versions	O
of	O
Cardano	B-Protocol
using	O
a	O
hard	O
fork	O
combinator	O
that	O
preserved	O
the	O
blockchain	B-Application
history	O
;	O
</s>
<s>
Ouroboros	B-General_Concept
Praos	O
(	O
2017	O
)	O
provided	O
security	O
against	O
fully-adaptive	O
corruption	O
in	O
the	O
semi-synchronous	O
model	O
.	O
</s>
<s>
In	O
2020	O
,	O
this	O
version	O
was	O
used	O
to	O
introduce	O
decentralized	O
block	O
production	O
on	O
Cardano	B-Protocol
by	O
stake	O
pools	O
;	O
</s>
<s>
Ouroboros	B-General_Concept
Genesis	O
(	O
2018	O
)	O
provides	O
security	O
with	O
a	O
dynamic	O
participation	O
model	O
;	O
</s>
<s>
Ouroboros	B-General_Concept
Chronos	O
(	O
2019	O
)	O
is	O
independent	O
of	O
global	O
time	O
;	O
</s>
<s>
Ouroboros	B-General_Concept
Crypsinous	O
(	O
2019	O
)	O
gives	O
higher	O
levels	O
of	O
privacy	O
.	O
</s>
<s>
Cardano	B-Protocol
's	O
founder	O
Charles	O
Hoskinson	O
has	O
described	O
the	O
Ouroboros	B-General_Concept
consensus	O
mechanism	O
as	O
energy	O
efficient	O
.	O
</s>
<s>
compared	O
Ouroboros	B-General_Concept
to	O
other	O
PoS	O
protocols	O
.	O
</s>
<s>
The	O
cryptocurrency	O
Polkadot	B-Protocol
uses	O
an	O
adapted	O
form	O
of	O
Ouroboros	B-General_Concept
called	O
Blind	O
Assignment	O
for	O
Blockchain	B-Application
Extension	O
.	O
</s>
