<s>
Lyra2	B-Algorithm
is	O
a	O
password	O
hashing	O
scheme	O
(	O
PHS	O
)	O
that	O
can	O
also	O
work	O
as	O
a	O
key	B-Algorithm
derivation	I-Algorithm
function	I-Algorithm
(	O
KDF	O
)	O
.	O
</s>
<s>
It	O
received	O
a	O
special	O
recognition	O
during	O
the	O
Password	O
Hashing	O
Competition	O
in	O
July	O
2015	O
,	O
which	O
was	O
won	O
by	O
Argon2	B-Algorithm
.	O
</s>
<s>
Lyra2	B-Algorithm
was	O
designed	O
by	O
Marcos	O
A	O
.	O
Simplicio	O
Jr.	O
,	O
Leonardo	O
C	O
.	O
Almeida	O
,	O
Ewerton	O
R	O
.	O
Andrade	O
,	O
Paulo	O
C	O
.	O
F	O
.	O
dos	O
Santos	O
,	O
and	O
Paulo	O
S	O
.	O
L	O
.	O
M	O
.	O
Barreto	O
from	O
Escola	O
Politécnica	O
da	O
Universidade	O
de	O
São	O
Paulo	O
.	O
</s>
<s>
Lyra2	B-Algorithm
preserves	O
the	O
security	O
,	O
efficiency	O
and	O
flexibility	O
of	O
its	O
predecessor	O
,	O
including	O
:	O
(	O
1	O
)	O
the	O
ability	O
to	O
configure	O
the	O
desired	O
amount	O
of	O
memory	O
,	O
processing	O
time	O
and	O
parallelism	B-Operating_System
to	O
be	O
used	O
by	O
the	O
algorithm	O
;	O
and	O
(	O
2	O
)	O
the	O
capacity	O
of	O
providing	O
a	O
high	O
memory	O
usage	O
with	O
a	O
processing	O
time	O
similar	O
to	O
that	O
obtained	O
with	O
scrypt	B-Algorithm
.	O
</s>
<s>
Lyra2	B-Algorithm
is	O
released	O
under	O
public	O
domain	O
,	O
and	O
provides	O
two	O
main	O
extensions	O
:	O
</s>
<s>
Capability	O
of	O
using	O
different	O
underlying	O
sponge	B-Algorithm
functions	I-Algorithm
depending	O
on	O
the	O
target	O
platform	O
(	O
e.g.	O
,	O
BLAKE2b	O
for	O
software	O
implementations	O
;	O
Keccak	B-Algorithm
for	O
hardware	O
implementations	O
;	O
BlaMka	O
for	O
additional	O
resistance	O
against	O
hardware	O
platforms	O
;	O
etc	O
.	O
)	O
</s>
<s>
As	O
any	O
PHS	O
,	O
Lyra2	B-Algorithm
takes	O
as	O
input	O
a	O
salt	O
and	O
a	O
password	O
,	O
creating	O
a	O
pseudorandom	B-Error_Name
output	O
that	O
can	O
then	O
be	O
used	O
as	O
key	O
material	O
for	O
cryptographic	O
algorithms	O
or	O
as	O
an	O
authentication	B-Protocol
string	O
.	O
</s>
<s>
The	O
construction	O
and	O
visitation	O
of	O
the	O
matrix	O
is	O
done	O
using	O
a	O
stateful	O
combination	O
of	O
the	O
absorbing	O
,	O
squeezing	O
and	O
duplexing	O
operations	O
of	O
the	O
underlying	O
sponge	B-Algorithm
(	O
i.e.	O
,	O
its	O
internal	O
state	O
is	O
never	O
reset	O
to	O
zero	O
)	O
,	O
ensuring	O
the	O
sequential	O
nature	O
of	O
the	O
whole	O
process	O
.	O
</s>
<s>
Also	O
,	O
the	O
number	O
of	O
times	O
the	O
matrix	O
's	O
cells	O
are	O
revisited	O
after	O
initialization	O
is	O
defined	O
by	O
the	O
user	O
,	O
allowing	O
Lyra2	B-Algorithm
's	O
execution	O
time	O
to	O
be	O
fine-tuned	O
according	O
to	O
the	O
target	O
platform	O
's	O
resources	O
.	O
</s>
<s>
Against	O
Lyra2	B-Algorithm
,	O
the	O
processing	O
cost	O
of	O
attacks	O
using	O
of	O
the	O
amount	O
of	O
memory	O
employed	O
by	O
a	O
legitimate	O
user	O
is	O
expected	O
to	O
be	O
between	O
and	O
,	O
the	O
latter	O
being	O
a	O
better	O
estimate	O
for	O
,	O
instead	O
of	O
the	O
achieved	O
when	O
the	O
amount	O
of	O
memory	O
is	O
,	O
where	O
is	O
a	O
user-defined	O
parameter	O
to	O
define	O
a	O
processing	O
time	O
.	O
</s>
<s>
This	O
compares	O
well	O
to	O
Scrypt	B-Algorithm
,	O
which	O
displays	O
a	O
cost	O
of	O
when	O
the	O
memory	O
usage	O
is	O
,	O
and	O
with	O
other	O
solutions	O
in	O
the	O
literature	O
,	O
for	O
which	O
the	O
results	O
are	O
usually	O
.	O
</s>
<s>
Nonetheless	O
,	O
in	O
practice	O
these	O
solutions	O
usually	O
involve	O
a	O
value	O
of	O
(	O
memory	O
usage	O
)	O
lower	O
than	O
those	O
attained	O
with	O
the	O
Lyra2	B-Algorithm
for	O
the	O
same	O
processing	O
time	O
.	O
</s>
<s>
The	O
processing	O
time	O
obtained	O
with	O
a	O
SSE	O
single-core	O
implementation	O
of	O
Lyra2	B-Algorithm
are	O
illustrated	O
in	O
the	O
hereby	O
shown	O
figure	O
.	O
</s>
<s>
The	O
results	O
depicted	O
correspond	O
to	O
the	O
average	O
execution	O
time	O
of	O
Lyra2	B-Algorithm
configured	O
with	O
,	O
,	O
bits	O
(	O
i.e.	O
,	O
the	O
inner	O
state	O
has	O
256	O
bits	O
)	O
,	O
and	O
different	O
and	O
settings	O
,	O
giving	O
an	O
overall	O
idea	O
of	O
possible	O
combinations	O
of	O
parameters	O
and	O
the	O
corresponding	O
usage	O
of	O
resources	O
.	O
</s>
<s>
As	O
shown	O
in	O
this	O
figure	O
,	O
Lyra2	B-Algorithm
is	O
able	O
to	O
execute	O
in	O
:	O
less	O
than	O
1	O
s	O
while	O
using	O
up	O
to	O
400	O
MB	O
(	O
with	O
and	O
)	O
or	O
up	O
to	O
1	O
GB	O
of	O
memory	O
(	O
with	O
and	O
)	O
;	O
or	O
in	O
less	O
than	O
5	O
s	O
with	O
1.6	O
GB	O
(	O
with	O
and	O
)	O
.	O
</s>
<s>
All	O
tests	O
were	O
performed	O
on	O
an	O
Intel	B-Device
Xeon	I-Device
E5-2430	I-Device
(	O
2.20GHz	O
with	O
12	O
Cores	O
,	O
64	O
bits	O
)	O
equipped	O
with	O
48	O
GB	O
of	O
DRAM	O
,	O
running	O
Ubuntu	B-Operating_System
14.04	O
LTS	O
64	O
bits	O
,	O
and	O
the	O
source	O
code	O
was	O
compiled	O
using	O
gcc	B-Application
4.9.2	O
.	O
</s>
