<s>
The	O
Lai	B-Algorithm
–	I-Algorithm
Massey	I-Algorithm
scheme	I-Algorithm
is	O
a	O
cryptographic	O
structure	O
used	O
in	O
the	O
design	O
of	O
block	O
ciphers	O
.	O
</s>
<s>
It	O
is	O
used	O
in	O
IDEA	B-Algorithm
and	O
IDEA	B-Algorithm
NXT	I-Algorithm
.	O
</s>
<s>
The	O
Lai-Massey	B-Algorithm
Scheme	I-Algorithm
is	O
similar	O
to	O
a	O
Feistel	B-Algorithm
Network	I-Algorithm
in	O
design	O
,	O
using	O
a	O
round	O
function	O
and	O
a	O
half-round	O
function	O
.	O
</s>
<s>
Due	O
to	O
its	O
design	O
,	O
it	O
has	O
an	O
advantage	O
over	O
a	O
Substitution-permutation	B-Algorithm
network	I-Algorithm
since	O
the	O
round-function	O
does	O
not	O
need	O
to	O
be	O
inverted	O
-	O
just	O
the	O
half-round	O
-	O
enabling	O
it	O
to	O
be	O
more	O
easily	O
inverted	O
,	O
and	O
enabling	O
the	O
round-function	O
to	O
be	O
arbitrarily	O
complex	O
.	O
</s>
<s>
The	O
encryption	O
and	O
decryption	O
processes	O
are	O
fairly	O
similar	O
,	O
decryption	O
instead	O
requiring	O
a	O
reversal	O
of	O
the	O
key	B-Algorithm
schedule	I-Algorithm
,	O
an	O
inverted	O
half-round	O
function	O
,	O
and	O
that	O
the	O
round	O
function	O
's	O
output	O
be	O
subtracted	O
instead	O
of	O
added	O
.	O
</s>
<s>
The	O
Lai	B-Algorithm
–	I-Algorithm
Massey	I-Algorithm
scheme	I-Algorithm
offers	O
security	O
properties	O
similar	O
to	O
those	O
of	O
the	O
Feistel	B-Algorithm
structure	I-Algorithm
.	O
</s>
<s>
It	O
also	O
shares	O
its	O
advantage	O
over	O
a	O
substitution	B-Algorithm
–	I-Algorithm
permutation	I-Algorithm
network	I-Algorithm
that	O
the	O
round	O
function	O
does	O
not	O
have	O
to	O
be	O
invertible	O
.	O
</s>
<s>
where	O
both	O
and	O
are	O
permutations	B-Algorithm
(	O
in	O
the	O
mathematical	O
sense	O
,	O
that	O
is	O
,	O
a	O
bijection	O
not	O
a	O
permutation	B-Algorithm
box	I-Algorithm
)	O
.	O
</s>
