<s>
In	O
1997	O
,	O
Moni	O
Naor	O
and	O
Omer	O
Reingold	O
described	O
efficient	O
constructions	O
for	O
various	O
cryptographic	O
primitives	O
in	O
private	B-Application
key	I-Application
as	O
well	O
as	O
public-key	B-Application
cryptography	I-Application
.	O
</s>
<s>
The	O
Naor	O
–	O
Reingold	O
function	O
can	O
be	O
used	O
as	O
the	O
basis	O
of	O
many	O
cryptographic	O
schemes	O
including	O
symmetric	B-Algorithm
encryption	I-Algorithm
,	O
authentication	O
and	O
digital	O
signatures	O
.	O
</s>
<s>
There	O
are	O
other	O
attacks	O
that	O
would	O
be	O
very	O
bad	O
for	O
a	O
pseudorandom	B-Algorithm
number	I-Algorithm
generator	I-Algorithm
:	O
the	O
user	O
expects	O
to	O
get	O
random	O
numbers	O
from	O
the	O
output	O
,	O
so	O
of	O
course	O
the	O
stream	O
should	O
not	O
be	O
predictable	O
,	O
but	O
even	O
more	O
,	O
it	O
should	O
be	O
indistinguishable	O
from	O
a	O
random	O
string	O
.	O
</s>
<s>
Let	O
be	O
the	O
discrepancy	B-Algorithm
of	O
the	O
set	O
.	O
</s>
