<s>
In	O
cryptography	O
,	O
the	O
term	O
ciphertext	B-General_Concept
expansion	I-General_Concept
refers	O
to	O
the	O
length	O
increase	O
of	O
a	O
message	O
when	O
it	O
is	O
encrypted	O
.	O
</s>
<s>
Many	O
modern	O
cryptosystems	O
cause	O
some	O
degree	O
of	O
expansion	O
during	O
the	O
encryption	O
process	O
,	O
for	O
instance	O
when	O
the	O
resulting	O
ciphertext	O
must	O
include	O
a	O
message-unique	O
Initialization	B-Algorithm
Vector	I-Algorithm
(	O
IV	O
)	O
.	O
</s>
<s>
Probabilistic	O
encryption	O
schemes	O
cause	O
ciphertext	B-General_Concept
expansion	I-General_Concept
,	O
as	O
the	O
set	O
of	O
possible	O
ciphertexts	O
is	O
necessarily	O
greater	O
than	O
the	O
set	O
of	O
input	O
plaintexts	O
.	O
</s>
<s>
Certain	O
schemes	O
,	O
such	O
as	O
Cocks	O
Identity	O
Based	O
Encryption	O
,	O
or	O
the	O
Goldwasser-Micali	B-Algorithm
cryptosystem	I-Algorithm
result	O
in	O
ciphertexts	O
hundreds	O
or	O
thousands	O
of	O
times	O
longer	O
than	O
the	O
plaintext	O
.	O
</s>
<s>
Ciphertext	B-General_Concept
expansion	I-General_Concept
may	O
be	O
offset	O
or	O
increased	O
by	O
other	O
processes	O
which	O
compress	O
or	O
expand	O
the	O
message	O
,	O
e.g.	O
,	O
data	B-General_Concept
compression	I-General_Concept
or	O
error	B-Error_Name
correction	I-Error_Name
coding	I-Error_Name
.	O
</s>
