<s>
Ethereum	B-Protocol
Classic	I-Protocol
is	O
a	O
blockchain-based	O
distributed	B-Architecture
computing	I-Architecture
platform	O
which	O
offers	O
smart	B-Application
contract	I-Application
(	O
scripting	O
)	O
functionality	O
.	O
</s>
<s>
It	O
is	O
open	B-License
source	I-License
and	O
supports	O
a	O
modified	O
version	O
of	O
Nakamoto	O
consensus	O
via	O
transaction-based	O
state	O
transitions	O
executed	O
on	O
a	O
public	O
Ethereum	B-Application
Virtual	B-Architecture
Machine	I-Architecture
(	O
EVM	O
)	O
.	O
</s>
<s>
Ethereum	B-Protocol
Classic	I-Protocol
maintains	O
the	O
original	O
,	O
unaltered	O
history	O
of	O
the	O
Ethereum	B-Application
network	O
.	O
</s>
<s>
The	O
Ethereum	B-Application
project	O
's	O
mainnet	O
initially	O
released	O
via	O
Frontier	O
on	O
30	O
July	O
2015	O
.	O
</s>
<s>
However	O
,	O
due	O
to	O
a	O
hack	O
of	O
a	O
third-party	O
project	O
,	O
The	B-Protocol
DAO	I-Protocol
,	O
the	O
Ethereum	B-Application
Foundation	I-Application
created	O
a	O
new	O
version	O
of	O
the	O
Ethereum	B-Application
mainnet	O
on	O
20	O
July	O
2016	O
with	O
an	O
irregular	O
state	O
change	O
implemented	O
that	O
erased	O
the	B-Protocol
DAO	I-Protocol
theft	O
from	O
the	O
Ethereum	B-Application
blockchain	B-Application
history	O
.	O
</s>
<s>
The	O
Ethereum	B-Application
Foundation	I-Application
applied	O
their	O
trademark	O
to	O
the	O
new	O
,	O
altered	O
version	O
of	O
the	O
Ethereum	B-Application
blockchain	B-Application
;	O
Ethereum	B-Application
(	O
code	O
:	O
ETH	O
)	O
.	O
</s>
<s>
The	O
older	O
,	O
unaltered	O
version	O
of	O
Ethereum	B-Application
was	O
renamed	O
and	O
continued	O
on	O
as	O
Ethereum	B-Protocol
Classic	I-Protocol
(	O
code	O
:	O
ETC	O
)	O
.	O
</s>
<s>
Ethereum	B-Protocol
Classic	I-Protocol
's	O
native	O
Ether	B-Application
token	O
is	O
a	O
cryptocurrency	O
traded	O
on	O
digital	O
currency	O
exchanges	O
under	O
the	O
currency	O
code	O
ETC	O
.	O
</s>
<s>
Ether	B-Application
is	O
created	O
as	O
a	O
reward	O
to	O
network	B-Protocol
nodes	I-Protocol
for	O
a	O
process	O
known	O
as	O
"	O
mining	O
"	O
,	O
which	O
validates	O
computations	O
performed	O
on	O
Ethereum	B-Protocol
Classic	I-Protocol
's	O
EVM	O
.	O
</s>
<s>
Implemented	O
on	O
11	O
December	O
2017	O
,	O
the	O
current	O
ETC	O
monetary	O
policy	O
seeks	O
the	O
same	O
goals	O
as	O
bitcoin	B-Protocol
of	O
being	O
mechanical	O
,	O
algorithmic	O
,	O
and	O
capped	O
.	O
</s>
<s>
Ethereum	B-Protocol
Classic	I-Protocol
provides	O
a	O
decentralized	O
Turing-complete	B-Algorithm
virtual	B-Architecture
machine	I-Architecture
,	O
the	O
Ethereum	B-Application
Virtual	B-Architecture
Machine	I-Architecture
(	O
EVM	O
)	O
,	O
which	O
can	O
execute	O
scripts	O
using	O
an	O
international	O
network	O
of	O
public	O
nodes	B-Protocol
.	O
</s>
<s>
The	O
virtual	B-Architecture
machine	I-Architecture
's	O
instruction	B-General_Concept
set	I-General_Concept
is	O
Turing-complete	B-Algorithm
in	O
contrast	O
to	O
others	O
like	O
bitcoin	B-Protocol
script	O
.	O
</s>
<s>
Several	O
codenamed	O
prototypes	O
of	O
the	O
Ethereum	B-Application
platform	O
were	O
developed	O
by	O
the	O
Ethereum	B-Application
Foundation	I-Application
,	O
as	O
part	O
of	O
their	O
proof-of-concept	O
series	O
,	O
prior	O
to	O
the	O
official	O
launch	O
of	O
the	O
Frontier	O
network	O
.	O
</s>
<s>
Ethereum	B-Protocol
Classic	I-Protocol
followed	O
this	O
codebase	O
after	O
the	B-Protocol
DAO	I-Protocol
incident	O
.	O
</s>
<s>
On	O
20	O
July	O
2016	O
,	O
as	O
a	O
result	O
of	O
the	O
exploitation	O
of	O
a	O
flaw	O
in	O
The	B-Protocol
DAO	I-Protocol
project	O
's	O
smart	B-Application
contract	I-Application
software	O
,	O
and	O
subsequent	O
theft	O
of	O
$50	O
million	O
worth	O
of	O
Ether	B-Application
,	O
the	O
Ethereum	B-Application
network	O
split	O
into	O
two	O
separate	O
blockchains	B-Application
–	O
the	O
altered	O
history	O
was	O
named	O
Ethereum	B-Application
(	O
ETH	O
)	O
and	O
the	O
unaltered	O
history	O
was	O
named	O
Ethereum	B-Protocol
Classic	I-Protocol
(	O
ETC	O
)	O
.	O
</s>
<s>
The	O
new	O
chain	O
with	O
the	O
altered	O
history	O
was	O
branded	O
as	O
Ethereum	B-Application
(	O
code	O
:	O
ETH	O
)	O
with	O
the	O
BIP-44	O
Coin	O
Index	O
60	O
and	O
EVM	O
Chain	O
ID	O
1	O
attributed	O
to	O
it	O
by	O
the	O
trademark-owning	O
Ethereum	B-Application
Foundation	I-Application
.	O
</s>
<s>
On	O
this	O
new	O
chain	O
,	O
the	O
history	O
of	O
the	O
theft	O
was	O
erased	O
from	O
the	O
Ethereum	B-Application
blockchain	B-Application
.	O
</s>
<s>
Some	O
members	O
of	O
the	O
Ethereum	B-Application
community	O
ignored	O
the	O
change	O
and	O
continued	O
to	O
participate	O
on	O
the	O
original	O
Ethereum	B-Application
network	O
.	O
</s>
<s>
The	O
non-fork	O
chain	O
with	O
an	O
unaltered	O
history	O
continued	O
on	O
as	O
Ethereum	B-Protocol
Classic	I-Protocol
(	O
code	O
:	O
ETC	O
)	O
with	O
the	O
BIP-44	O
Coin	O
Index	O
61	O
and	O
EVM	O
Chain	O
ID	O
61	O
.	O
</s>
<s>
On	O
28	O
May	O
2016	O
,	O
a	O
paper	O
was	O
released	O
detailing	O
security	O
vulnerabilities	O
with	O
the	B-Protocol
DAO	I-Protocol
that	O
could	O
allow	O
Ether	B-Application
to	O
be	O
stolen	O
.	O
</s>
<s>
On	O
12	O
June	O
2016	O
,	O
Stephan	O
Tual	O
publicly	O
claimed	O
that	O
the	B-Protocol
DAO	I-Protocol
funds	O
were	O
safe	O
despite	O
the	O
newly-discovered	O
critical	O
security	O
flaw	O
.	O
</s>
<s>
On	O
15	O
July	O
2016	O
,	O
a	O
short	O
notice	O
on-chain	O
vote	O
was	O
held	O
on	O
the	B-Protocol
DAO	I-Protocol
hard	O
fork	O
.	O
</s>
<s>
Of	O
the	O
82,054,716	O
ETH	O
in	O
existence	O
,	O
only	O
4,542,416	O
voted	O
,	O
for	O
a	O
total	O
voter	O
turn	O
out	O
of	O
5.5	O
%	O
of	O
the	O
total	O
supply	O
on	O
16	O
July	O
2016	O
;	O
3,964,516	O
ETH	O
(	O
87%	O
)	O
voted	O
in	O
favor	O
,	O
1/4	O
of	O
which	O
came	O
from	O
a	O
single	O
address	O
,	O
and	O
577,899	O
ETH	O
(	O
13%	O
)	O
opposed	O
the	B-Protocol
DAO	I-Protocol
fork	O
.	O
</s>
<s>
The	O
expedited	O
process	O
of	O
the	O
carbon	O
vote	O
drew	O
criticism	O
from	O
opponents	O
of	O
the	B-Protocol
DAO	I-Protocol
fork	O
.	O
</s>
<s>
Proponents	O
of	O
the	O
fork	O
were	O
quick	O
to	O
market	O
the	O
vote	O
as	O
an	O
effective	O
consensus	O
mechanism	O
,	O
pushing	O
forward	O
with	O
the	B-Protocol
DAO	I-Protocol
fork	O
four	O
days	O
later	O
.	O
</s>
<s>
The	O
first	O
Ethereum	B-Protocol
Classic	I-Protocol
block	O
that	O
was	O
not	O
included	O
in	O
the	O
forked	O
Ethereum	B-Application
chain	O
was	O
block	O
number	O
1	O
,	O
920	O
,	O
000	O
,	O
which	O
was	O
generated	O
by	O
Ethereum	B-Protocol
Classic	I-Protocol
miners	O
on	O
20	O
July	O
2016	O
.	O
</s>
<s>
A	O
mechanism	O
called	O
the	O
"	O
Difficulty	O
Bomb	O
"	O
was	O
designed	O
to	O
push	O
the	O
Ethereum	B-Application
chain	O
from	O
proof-of-work	O
consensus	O
mechanism	O
to	O
proof-of-stake	O
in	O
the	O
future	O
by	O
exponentially	O
increasing	O
the	O
difficulty	O
of	O
mining	O
.	O
</s>
<s>
While	O
Ethereum	B-Protocol
Classic	I-Protocol
participants	O
debated	O
the	O
merits	O
of	O
the	O
Difficulty	O
Bomb	O
,	O
a	O
network	O
upgrade	O
called	O
"	O
Die	O
Hard	O
"	O
at	O
block	O
3,000,000	O
delayed	O
the	O
effects	O
of	O
the	O
mechanism	O
.	O
</s>
<s>
Once	O
the	O
network	O
participants	O
came	O
to	O
consensus	O
on	O
the	O
issue	O
,	O
Ethereum	B-Protocol
Classic	I-Protocol
upgraded	O
its	O
network	O
on	O
block	O
5,900,000	O
to	O
permanently	O
defuse	O
the	O
Difficulty	O
Bomb	O
.	O
</s>
<s>
In	O
an	O
attempt	O
to	O
modernize	O
the	O
Ethereum	B-Protocol
Classic	I-Protocol
protocol	O
,	O
several	O
protocol	O
upgrades	O
were	O
scheduled	O
to	O
activate	O
features	O
that	O
the	O
Ethereum	B-Application
network	O
already	O
enabled	O
over	O
the	O
past	O
years	O
.	O
</s>
<s>
Finally	O
,	O
with	O
the	O
Phoenix	O
upgrade	O
,	O
Ethereum	B-Protocol
Classic	I-Protocol
achieved	O
protocol	O
parity	O
with	O
Ethereum	B-Application
,	O
allowing	O
for	O
fully	O
cross-compatible	O
applications	O
between	O
the	O
two	O
networks	O
.	O
</s>
<s>
After	O
a	O
series	O
of	O
51%	O
attacks	O
on	O
the	O
Ethereum	B-Protocol
Classic	I-Protocol
network	O
in	O
2020	O
,	O
a	O
change	O
to	O
the	O
underlying	O
Ethash	B-Application
mining	O
algorithm	O
was	O
considered	O
by	O
the	O
community	O
to	O
prevent	O
being	O
a	O
minority	O
proof-of-work	O
chain	O
in	O
the	O
Ethash	B-Application
mining	O
algorithm	O
where	O
Ethereum	B-Application
is	O
dominating	O
the	O
hashrate	O
.	O
</s>
<s>
After	O
evaluating	O
various	O
options	O
such	O
as	O
Monero	B-Protocol
's	I-Protocol
RandomX	O
or	O
the	O
standardized	O
SHA-3-256	B-Algorithm
,	O
it	O
was	O
eventually	O
decided	O
to	O
double	O
the	O
Ethash	B-Application
epoch	O
duration	O
from	O
30,000	O
to	O
60,000	O
in	O
order	O
to	O
reduce	O
the	O
DAG	O
size	O
and	O
prevent	O
Ethash	B-Application
miners	O
to	O
easily	O
switch	O
to	O
Ethereum	B-Protocol
Classic	I-Protocol
.	O
</s>
<s>
This	O
modified	O
Ethash	B-Application
is	O
also	O
referred	O
to	O
as	O
ETChash	O
or	O
Thanos	O
upgrade	O
.	O
</s>
<s>
As	O
with	O
other	O
cryptocurrencies	O
,	O
the	O
validity	O
of	O
each	O
ether	B-Application
is	O
provided	O
by	O
a	O
blockchain	B-Application
,	O
which	O
is	O
a	O
continuously	O
growing	O
list	O
of	O
records	O
,	O
called	O
"	O
blocks	O
"	O
,	O
which	O
are	O
linked	O
and	O
secured	O
using	O
cryptography	O
.	O
</s>
<s>
By	O
design	O
,	O
the	O
blockchain	B-Application
is	O
inherently	O
resistant	O
to	O
modification	O
of	O
the	O
data	O
.	O
</s>
<s>
Unlike	O
Bitcoin	B-Protocol
,	O
Ethereum	B-Protocol
Classic	I-Protocol
operates	O
using	O
accounts	O
and	O
balances	O
in	O
a	O
manner	O
called	O
state	O
transitions	O
.	O
</s>
<s>
This	O
does	O
not	O
rely	O
upon	O
unspent	B-Protocol
transaction	I-Protocol
outputs	I-Protocol
(	O
UTXOs	O
)	O
.	O
</s>
<s>
The	O
state	O
is	O
not	O
stored	O
on	O
the	O
blockchain	B-Application
,	O
it	O
is	O
stored	O
in	O
a	O
separate	O
Merkle	B-Algorithm
Patricia	O
tree	O
.	O
</s>
<s>
A	O
cryptocurrency	B-Protocol
wallet	I-Protocol
stores	O
the	O
public	B-Application
and	I-Application
private	I-Application
"	I-Application
keys	I-Application
"	I-Application
or	O
"	O
addresses	O
"	O
which	O
can	O
be	O
used	O
to	O
receive	O
or	O
spend	O
Ether	B-Application
.	O
</s>
<s>
In	O
the	O
Ethereum	B-Application
tech	O
stack	O
,	O
this	O
is	O
unnecessary	O
as	O
it	O
does	O
not	O
operate	O
in	O
a	O
UTXO	B-Protocol
scheme	O
.	O
</s>
<s>
With	O
the	O
private	B-Application
key	I-Application
,	O
it	O
is	O
possible	O
to	O
write	O
in	O
the	O
blockchain	B-Application
,	O
effectively	O
making	O
an	O
ether	B-Application
transaction	O
.	O
</s>
<s>
To	O
send	O
Ether	B-Application
to	O
an	O
account	O
,	O
the	O
Keccak-256	B-Algorithm
hash	O
of	O
the	O
public	B-Application
key	I-Application
of	O
that	O
account	O
is	O
needed	O
.	O
</s>
<s>
Ether	B-Application
accounts	O
are	O
pseudonymous	O
in	O
that	O
they	O
are	O
not	O
linked	O
to	O
individual	O
persons	O
,	O
but	O
rather	O
to	O
one	O
or	O
more	O
specific	O
addresses	O
.	O
</s>
<s>
ETC	O
is	O
a	O
fundamental	O
token	O
for	O
operation	O
of	O
Ethereum	B-Protocol
Classic	I-Protocol
,	O
which	O
thereby	O
provides	O
a	O
public	O
distributed	O
ledger	O
for	O
transactions	O
.	O
</s>
<s>
Within	O
the	O
context	O
of	O
Ethereum	B-Protocol
Classic	I-Protocol
it	O
might	O
be	O
called	O
ether	B-Application
,	O
but	O
it	O
should	O
not	O
be	O
confused	O
with	O
ETH	O
,	O
which	O
is	O
also	O
called	O
ether	B-Application
.	O
</s>
<s>
It	O
is	O
also	O
used	O
to	O
pay	O
for	O
transaction	O
fees	O
and	O
computational	O
services	O
on	O
the	O
Ethereum	B-Protocol
Classic	I-Protocol
network	O
.	O
</s>
<s>
Ethereum	B-Protocol
Classic	I-Protocol
addresses	O
are	O
composed	O
of	O
the	O
prefix	O
"	O
0x	O
"	O
,	O
a	O
common	O
identifier	O
for	O
hexadecimal	O
,	O
concatenated	O
with	O
the	O
rightmost	O
20	O
bytes	O
of	O
the	O
Keccak-256	B-Algorithm
hash	O
(	O
big	O
endian	O
)	O
of	O
the	O
ECDSA	O
public	B-Application
key	I-Application
(	O
the	O
curve	O
used	O
is	O
the	O
so-called	O
secp256k1	O
,	O
the	O
same	O
as	O
bitcoin	B-Protocol
)	O
.	O
</s>
<s>
An	O
example	O
of	O
an	O
Ethereum	B-Protocol
Classic	I-Protocol
address	O
is	O
0xb794f5ea0ba39494ce839613fffba74279579268	O
.	O
</s>
<s>
User	O
accounts	O
are	O
indistinguishable	O
from	O
contract	O
accounts	O
given	O
only	O
an	O
address	O
for	O
each	O
and	O
no	O
blockchain	B-Application
data	O
.	O
</s>
<s>
Any	O
valid	O
Keccak-256	B-Algorithm
hash	O
put	O
into	O
the	O
described	O
format	O
is	O
valid	O
,	O
even	O
if	O
it	O
does	O
not	O
correspond	O
to	O
an	O
account	O
with	O
a	O
private	B-Application
key	I-Application
or	O
a	O
contract	O
.	O
</s>
<s>
This	O
is	O
unlike	O
bitcoin	B-Protocol
,	O
which	O
uses	O
base58check	O
to	O
ensure	O
that	O
addresses	O
are	O
properly	O
typed	O
.	O
</s>
<s>
On	O
11	O
December	O
2017	O
,	O
the	O
total	O
supply	O
of	O
Ether	B-Application
on	O
Ethereum	B-Protocol
Classic	I-Protocol
was	O
hard	O
capped	O
at	O
ETC	O
210,700,000	O
via	O
the	O
Gotham	O
hard	O
fork	O
upgrade	O
.	O
</s>
<s>
This	O
added	O
a	O
bitcoin-inspired	O
deflationary	O
emission	O
schedule	O
that	O
is	O
documented	O
in	O
Ethereum	B-Protocol
Classic	I-Protocol
Improvement	O
Proposal	O
(	O
ECIP	O
)	O
1017	O
.	O
</s>
<s>
The	O
Ethereum	B-Protocol
Classic	I-Protocol
Improvement	O
Proposal	O
(	O
ECIP	O
)	O
process	O
enables	O
engineers	O
and	O
computer	O
scientists	O
to	O
propose	O
modifications	O
,	O
upgrades	O
,	O
or	O
fixes	O
.	O
</s>
<s>
The	O
people	O
who	O
continued	O
with	O
Ethereum	B-Protocol
Classic	I-Protocol
advocate	O
for	O
blockchain	B-Application
immutability	O
,	O
and	O
the	O
concept	O
that	O
"	O
code	O
is	O
law	O
"	O
against	O
the	O
pro-fork	O
side	O
(	O
Ethereum	B-Application
)	O
which	O
largely	O
argued	O
for	O
extra-protocol	O
intentionality	O
,	O
decentralized	O
decision-making	O
,	O
and	O
conflict	O
resolution	O
.	O
</s>
<s>
On	O
20	O
July	O
2016	O
,	O
due	O
to	O
reliance	O
on	O
the	O
same	O
clients	O
,	O
the	B-Protocol
DAO	I-Protocol
fork	O
created	O
a	O
replay	O
attack	O
where	O
a	O
transaction	O
was	O
broadcast	O
on	O
both	O
the	O
ETC	O
and	O
ETH	O
networks	O
.	O
</s>
<s>
On	O
13	O
January	O
2017	O
,	O
the	O
Ethereum	B-Protocol
Classic	I-Protocol
network	O
was	O
updated	O
to	O
resolve	O
transaction	O
replay	O
attacks	O
.	O
</s>
<s>
On	O
29	O
June	O
2017	O
,	O
the	O
Ethereum	B-Protocol
Classic	I-Protocol
Twitter	O
account	O
made	O
a	O
public	O
statement	O
indicating	O
reason	O
to	O
believe	O
that	O
the	O
website	O
for	O
Classic	O
Ether	B-Application
Wallet	O
had	O
been	O
compromised	O
.	O
</s>
<s>
The	O
Ethereum	B-Protocol
Classic	I-Protocol
Twitter	O
account	O
confirmed	O
the	O
details	O
released	O
via	O
Threatpost	O
.	O
</s>
<s>
The	O
Ethereum	B-Protocol
Classic	I-Protocol
team	O
worked	O
with	O
Cloudflare	B-Application
to	O
place	O
a	O
warning	O
on	O
the	O
compromised	O
domain	O
warning	O
users	O
of	O
the	O
phishing	O
attack	O
.	O
</s>
<s>
ETC	O
has	O
experienced	O
multiple	O
51%	O
double-spending	B-Operating_System
attacks	O
throughout	O
its	O
history	O
.	O
</s>
<s>
The	O
first	O
significant	O
attack	O
occurred	O
in	O
January	O
2019	O
,	O
when	O
Ethereum	B-Protocol
Classic	I-Protocol
was	O
subject	O
to	O
double-spending	B-Operating_System
attacks	O
and	O
an	O
estimated	O
$1.1	O
million	O
worth	O
of	O
ETC	O
was	O
double-spent	O
.	O
</s>
<s>
In	O
response	O
,	O
the	O
Ethereum	B-Protocol
Classic	I-Protocol
team	O
initiated	O
several	O
network	O
upgrades	O
,	O
including	O
the	O
adoption	O
of	O
a	O
modified	O
version	O
of	O
the	O
Proof	O
of	O
Work	O
(	O
PoW	O
)	O
consensus	O
algorithm	O
called	O
"	O
ECIP-1049	O
Keccak256.	O
"	O
</s>
