<s>
In	O
cryptography	O
,	O
scrypt	B-Algorithm
(	O
pronounced	O
"	O
ess	O
crypt	B-Algorithm
"	O
)	O
is	O
a	O
password-based	B-Algorithm
key	I-Algorithm
derivation	I-Algorithm
function	I-Algorithm
created	O
by	O
Colin	O
Percival	O
in	O
March	O
2009	O
,	O
originally	O
for	O
the	O
Tarsnap	B-General_Concept
online	O
backup	O
service	O
.	O
</s>
<s>
The	O
algorithm	O
was	O
specifically	O
designed	O
to	O
make	O
it	O
costly	O
to	O
perform	O
large-scale	O
custom	B-General_Concept
hardware	I-General_Concept
attacks	I-General_Concept
by	O
requiring	O
large	O
amounts	O
of	O
memory	O
.	O
</s>
<s>
In	O
2016	O
,	O
the	O
scrypt	B-Algorithm
algorithm	O
was	O
published	O
by	O
IETF	O
as	O
RFC	O
7914	O
.	O
</s>
<s>
A	O
simplified	O
version	O
of	O
scrypt	B-Algorithm
is	O
used	O
as	O
a	O
proof-of-work	O
scheme	O
by	O
a	O
number	O
of	O
cryptocurrencies	O
,	O
first	O
implemented	O
by	O
an	O
anonymous	O
programmer	O
called	O
ArtForz	O
in	O
Tenebrix	O
and	O
followed	O
by	O
Fairbrix	B-Protocol
and	O
Litecoin	B-Protocol
soon	O
after	O
.	O
</s>
<s>
A	O
password-based	B-Algorithm
key	I-Algorithm
derivation	I-Algorithm
function	I-Algorithm
(	O
password-based	O
KDF	O
)	O
is	O
generally	O
designed	O
to	O
be	O
computationally	O
intensive	O
,	O
so	O
that	O
it	O
takes	O
a	O
relatively	O
long	O
time	O
to	O
compute	O
(	O
say	O
on	O
the	O
order	O
of	O
several	O
hundred	O
milliseconds	O
)	O
.	O
</s>
<s>
They	O
are	O
therefore	O
easily	O
and	O
cheaply	O
implemented	O
in	O
hardware	O
(	O
for	O
instance	O
on	O
an	O
ASIC	O
or	O
even	O
an	O
FPGA	B-Architecture
)	O
.	O
</s>
<s>
The	O
scrypt	B-Algorithm
function	O
is	O
designed	O
to	O
hinder	O
such	O
attempts	O
by	O
raising	O
the	O
resource	O
demands	O
of	O
the	O
algorithm	O
.	O
</s>
<s>
The	O
large	O
memory	O
requirements	O
of	O
scrypt	B-Algorithm
come	O
from	O
a	O
large	O
vector	O
of	O
pseudorandom	B-Error_Name
bit	O
strings	O
that	O
are	O
generated	O
as	O
part	O
of	O
the	O
algorithm	O
.	O
</s>
<s>
Once	O
the	O
vector	O
is	O
generated	O
,	O
the	O
elements	O
of	O
it	O
are	O
accessed	O
in	O
a	O
pseudo-random	B-Error_Name
order	O
and	O
combined	O
to	O
produce	O
the	O
derived	O
key	O
.	O
</s>
<s>
The	O
idea	O
behind	O
scrypt	B-Algorithm
is	O
to	O
deliberately	O
make	O
this	O
trade-off	O
costly	O
in	O
either	O
direction	O
.	O
</s>
<s>
Where	O
Salsa20/8	B-Algorithm
''	O
is	O
the	O
8-round	O
version	O
of	O
Salsa20	B-Algorithm
.	O
</s>
<s>
Scrypt	B-Algorithm
is	O
used	O
in	O
many	O
cryptocurrencies	O
as	O
a	O
proof-of-work	O
algorithm	O
(	O
more	O
precisely	O
,	O
as	O
the	O
hash	O
function	O
in	O
the	O
Hashcash	O
proof-of-work	O
algorithm	O
)	O
.	O
</s>
<s>
It	O
was	O
first	O
implemented	O
for	O
Tenebrix	O
(	O
released	O
in	O
September	O
2011	O
)	O
and	O
served	O
as	O
the	O
basis	O
for	O
Litecoin	B-Protocol
and	O
Dogecoin	O
,	O
which	O
also	O
adopted	O
its	O
scrypt	B-Algorithm
algorithm	O
.	O
</s>
<s>
Mining	O
of	O
cryptocurrencies	O
that	O
use	O
scrypt	B-Algorithm
is	O
often	O
performed	O
on	O
graphics	B-Architecture
processing	I-Architecture
units	I-Architecture
(	O
GPUs	B-Architecture
)	O
since	O
GPUs	B-Architecture
tend	O
to	O
have	O
significantly	O
more	O
processing	O
power	O
(	O
for	O
some	O
algorithms	O
)	O
compared	O
to	O
the	O
CPU	O
.	O
</s>
<s>
This	O
led	O
to	O
shortages	O
of	O
high	O
end	O
GPUs	B-Architecture
due	O
to	O
the	O
rising	O
price	O
of	O
these	O
currencies	O
in	O
the	O
months	O
of	O
November	O
and	O
December	O
2013	O
.	O
</s>
<s>
As	O
of	O
May	O
2014	O
,	O
specialized	O
ASIC	O
mining	O
hardware	O
is	O
available	O
for	O
scrypt-based	O
cryptocurrencies	O
.	O
</s>
<s>
The	O
scrypt	B-Algorithm
utility	O
was	O
written	O
in	O
May	O
2009	O
by	O
Colin	O
Percival	O
as	O
a	O
demonstration	O
of	O
the	O
scrypt	B-Algorithm
key	B-Algorithm
derivation	I-Algorithm
function	I-Algorithm
.	O
</s>
<s>
It	O
's	O
available	O
in	O
most	O
Linux	B-Application
and	O
BSD	B-Operating_System
distributions	O
.	O
</s>
