<s>
In	O
cryptography	O
,	O
the	O
Full	B-Algorithm
Domain	I-Algorithm
Hash	I-Algorithm
(	O
FDH	O
)	O
is	O
an	O
RSA-based	O
signature	O
scheme	O
that	O
follows	O
the	O
hash-and-sign	O
paradigm	O
.	O
</s>
<s>
It	O
is	O
provably	O
secure	O
(	O
i.e.	O
,	O
is	O
existentially	O
unforgeable	O
under	O
adaptive	O
chosen-message	O
attacks	O
)	O
in	O
the	O
random	B-Application
oracle	I-Application
model	I-Application
.	O
</s>
<s>
FDH	O
involves	O
hashing	O
a	O
message	O
using	O
a	O
function	O
whose	O
image	O
size	O
equals	O
the	O
size	O
of	O
the	O
RSA	B-Architecture
modulus	O
,	O
and	O
then	O
raising	O
the	O
result	O
to	O
the	O
secret	O
RSA	B-Architecture
exponent	O
.	O
</s>
<s>
In	O
the	O
random	B-Application
oracle	I-Application
model	I-Application
,	O
if	O
RSA	B-Architecture
is	O
-secure	O
,	O
then	O
the	O
full	B-Algorithm
domain	I-Algorithm
hash	I-Algorithm
RSA	B-Architecture
signature	O
scheme	O
is	O
-secure	O
where	O
,	O
</s>
<s>
This	O
means	O
that	O
if	O
there	O
exists	O
an	O
algorithm	O
that	O
can	O
forge	O
a	O
new	O
FDH	O
signature	O
that	O
runs	O
in	O
time	O
t	O
,	O
computes	O
at	O
most	O
hashes	O
,	O
asks	O
for	O
at	O
most	O
signatures	O
and	O
succeeds	O
with	O
probability	O
,	O
then	O
there	O
must	O
also	O
exist	O
an	O
algorithm	O
that	O
breaks	O
RSA	B-Architecture
with	O
probability	O
in	O
time	O
.	O
</s>
