<s>
In	O
cryptography	O
,	O
Merkle	B-Protocol
's	I-Protocol
Puzzles	I-Protocol
is	O
an	O
early	O
construction	O
for	O
a	O
public-key	B-Application
cryptosystem	I-Application
,	O
a	O
protocol	O
devised	O
by	O
Ralph	O
Merkle	O
in	O
1974	O
and	O
published	O
in	O
1978	O
.	O
</s>
<s>
The	O
parameters	O
of	O
the	O
puzzle	O
game	O
can	O
be	O
chosen	O
to	O
make	O
it	O
considerably	O
harder	O
to	O
for	O
an	O
eavesdropper	O
to	O
break	O
the	O
code	O
than	O
for	O
the	O
parties	O
to	O
communicate	O
,	O
but	O
Merkle	B-Protocol
puzzles	I-Protocol
do	O
not	O
provide	O
the	O
enormous	O
qualitative	O
differences	O
in	O
difficulty	O
that	O
are	O
required	O
for	O
(	O
and	O
define	O
)	O
security	O
in	O
modern	O
cryptography	O
.	O
</s>
<s>
However	O
,	O
this	O
scheme	O
has	O
the	O
distinction	O
of	O
being	O
one	O
of	O
the	O
first	O
examples	O
of	O
public-key	B-Application
cryptography	I-Application
,	O
and	O
was	O
an	O
inspiration	O
for	O
the	O
Diffie-Hellman	B-Protocol
key	I-Protocol
exchange	I-Protocol
protocol	O
,	O
which	O
has	O
much	O
higher	O
complexity	O
,	O
relying	O
on	O
the	O
discrete	O
logarithm	O
problem	O
.	O
</s>
