<s>
In	O
cryptography	O
,	O
a	O
zero-knowledge	B-General_Concept
password	I-General_Concept
proof	I-General_Concept
(	O
ZKPP	B-General_Concept
)	O
is	O
a	O
type	O
of	O
zero-knowledge	B-Protocol
proof	I-Protocol
that	O
allows	O
one	O
party	O
(	O
the	O
prover	O
)	O
to	O
prove	O
to	O
another	O
party	O
(	O
the	O
verifier	O
)	O
that	O
it	O
knows	O
a	O
value	O
of	O
a	O
password	O
,	O
without	O
revealing	O
anything	O
other	O
than	O
the	O
fact	O
that	O
it	O
knows	O
the	O
password	O
to	O
the	O
verifier	O
.	O
</s>
<s>
The	O
term	O
is	O
defined	O
in	O
IEEE	O
P1363.2	O
,	O
in	O
reference	O
to	O
one	O
of	O
the	O
benefits	O
of	O
using	O
a	O
password-authenticated	B-Protocol
key	I-Protocol
exchange	I-Protocol
(	O
PAKE	B-Protocol
)	O
protocol	O
that	O
is	O
secure	O
against	O
off-line	O
dictionary	O
attacks	O
.	O
</s>
<s>
A	O
ZKPP	B-General_Concept
prevents	O
any	O
party	O
from	O
verifying	O
guesses	O
for	O
the	O
password	O
without	O
interacting	O
with	O
a	O
party	O
that	O
knows	O
it	O
and	O
,	O
in	O
the	O
optimal	O
case	O
,	O
provides	O
exactly	O
one	O
guess	O
in	O
each	O
interaction	O
.	O
</s>
<s>
A	O
common	O
use	O
of	O
a	O
zero-knowledge	B-General_Concept
password	I-General_Concept
proof	I-General_Concept
is	O
in	O
authentication	O
systems	O
where	O
one	O
party	O
wants	O
to	O
prove	O
its	O
identity	O
to	O
a	O
second	O
party	O
using	O
a	O
password	O
but	O
does	O
n't	O
want	O
the	O
second	O
party	O
or	O
anybody	O
else	O
to	O
learn	O
anything	O
about	O
the	O
password	O
.	O
</s>
<s>
The	O
first	O
methods	O
to	O
demonstrate	O
a	O
ZKPP	B-General_Concept
were	O
the	O
encrypted	B-Protocol
key	I-Protocol
exchange	I-Protocol
methods	O
(	O
EKE	O
)	O
described	O
by	O
Steven	O
M	O
.	O
Bellovin	O
and	O
Michael	O
Merritt	O
in	O
1992	O
.	O
</s>
<s>
A	O
considerable	O
number	O
of	O
refinements	O
,	O
alternatives	O
,	O
and	O
variations	O
in	O
the	O
growing	O
class	O
of	O
password-authenticated	B-Protocol
key	I-Protocol
agreement	I-Protocol
methods	O
were	O
developed	O
in	O
subsequent	O
years	O
.	O
</s>
