<s>
ZIP	B-Application
is	O
an	O
archive	O
file	O
format	O
that	O
supports	O
lossless	B-Algorithm
data	I-Algorithm
compression	I-Algorithm
.	O
</s>
<s>
A	O
ZIP	B-General_Concept
file	I-General_Concept
may	O
contain	O
one	O
or	O
more	O
files	O
or	O
directories	O
that	O
may	O
have	O
been	O
compressed	O
.	O
</s>
<s>
The	O
ZIP	B-General_Concept
file	I-General_Concept
format	I-General_Concept
permits	O
a	O
number	O
of	O
compression	B-General_Concept
algorithms	I-General_Concept
,	O
though	O
DEFLATE	B-Algorithm
is	O
the	O
most	O
common	O
.	O
</s>
<s>
This	O
format	O
was	O
originally	O
created	O
in	O
1989	O
and	O
was	O
first	O
implemented	O
in	O
PKWARE	O
,	O
Inc.	O
'	O
s	O
PKZIP	B-Application
utility	O
,	O
as	O
a	O
replacement	O
for	O
the	O
previous	O
ARC	B-Application
compression	B-General_Concept
format	O
by	O
Thom	B-Application
Henderson	I-Application
.	O
</s>
<s>
The	O
ZIP	B-Application
format	O
was	O
then	O
quickly	O
supported	O
by	O
many	O
software	O
utilities	O
other	O
than	O
PKZIP	B-Application
.	O
</s>
<s>
Microsoft	O
has	O
included	O
built-in	O
ZIP	B-Application
support	O
(	O
under	O
the	O
name	O
"	O
compressed	B-General_Concept
folders	I-General_Concept
"	O
)	O
in	O
versions	O
of	O
Microsoft	B-Application
Windows	I-Application
since	O
1998	O
via	O
the	O
"	O
Plus	B-Application
!	I-Application
</s>
<s>
Apple	O
has	O
included	O
built-in	O
ZIP	B-Application
support	O
in	O
Mac	O
OS	O
X	O
10.3	O
(	O
via	O
BOMArchiveHelper	O
,	O
now	O
Archive	O
Utility	O
)	O
and	O
later	O
.	O
</s>
<s>
Most	O
free	O
operating	O
systems	O
have	O
built	O
in	O
support	O
for	O
ZIP	B-Application
in	O
similar	O
manners	O
to	O
Windows	O
and	O
Mac	B-Application
OS	I-Application
X	O
.	O
</s>
<s>
ZIP	B-General_Concept
files	I-General_Concept
generally	O
use	O
the	O
file	O
extensions	O
or	O
and	O
the	O
MIME	B-Protocol
media	O
type	O
.	O
</s>
<s>
ZIP	B-Application
is	O
used	O
as	O
a	O
base	O
file	O
format	O
by	O
many	O
programs	O
,	O
usually	O
under	O
a	O
different	O
name	O
.	O
</s>
<s>
When	O
navigating	O
a	O
file	B-Application
system	I-Application
via	O
a	O
user	O
interface	O
,	O
graphical	O
icons	O
representing	O
ZIP	B-General_Concept
files	I-General_Concept
often	O
appear	O
as	O
a	O
document	O
or	O
other	O
object	O
prominently	O
featuring	O
a	O
zipper	B-Application
.	O
</s>
<s>
The	O
format	O
was	O
created	O
after	O
Systems	O
Enhancement	O
Associates	O
(	O
SEA	O
)	O
filed	O
a	O
lawsuit	O
against	O
PKWARE	O
claiming	O
that	O
the	O
latter	O
's	O
archiving	O
products	O
,	O
named	O
PKARC	O
,	O
were	O
derivatives	O
of	O
SEA	O
's	O
ARC	B-Application
archiving	O
system	O
.	O
</s>
<s>
The	O
name	O
"	O
zip	B-Application
"	O
(	O
meaning	O
"	O
move	O
at	O
high	O
speed	O
"	O
)	O
was	O
suggested	O
by	O
Katz	O
's	O
friend	O
,	O
Robert	O
Mahoney	O
.	O
</s>
<s>
They	O
wanted	O
to	O
imply	O
that	O
their	O
product	O
would	O
be	O
faster	O
than	O
ARC	B-Application
and	O
other	O
compression	B-General_Concept
formats	I-General_Concept
of	O
the	O
time	O
.	O
</s>
<s>
By	O
distributing	O
the	O
zip	B-General_Concept
file	I-General_Concept
format	I-General_Concept
within	O
APPNOTE.TXT	O
,	O
compatibility	O
with	O
the	O
zip	B-General_Concept
file	I-General_Concept
format	I-General_Concept
proliferated	O
widely	O
on	O
the	O
public	O
Internet	O
during	O
the	O
1990s	O
.	O
</s>
<s>
The	O
.ZIP	B-General_Concept
File	I-General_Concept
Format	O
Specification	O
has	O
its	O
own	O
version	O
number	O
,	O
which	O
does	O
not	O
necessarily	O
correspond	O
to	O
the	O
version	O
numbers	O
for	O
the	O
PKZIP	B-Application
tool	O
,	O
especially	O
with	O
PKZIP	B-Application
6	O
or	O
later	O
.	O
</s>
<s>
At	O
various	O
times	O
,	O
PKWARE	O
has	O
added	O
preliminary	O
features	O
that	O
allow	O
PKZIP	B-Application
products	O
to	O
extract	O
archives	O
using	O
advanced	O
features	O
,	O
but	O
PKZIP	B-Application
products	O
that	O
create	O
such	O
archives	O
are	O
not	O
made	O
available	O
until	O
the	O
next	O
major	O
release	O
.	O
</s>
<s>
The	O
.ZIP	B-General_Concept
file	I-General_Concept
format	O
specification	O
is	O
formally	O
named	O
"	O
APPNOTE	O
-	O
.ZIP	B-General_Concept
File	I-General_Concept
Format	O
Specification	O
"	O
and	O
it	O
is	O
published	O
on	O
the	O
PKWARE.com	O
website	O
since	O
the	O
late	O
1990s	O
.	O
</s>
<s>
Specifications	O
of	O
some	O
features	O
such	O
as	O
BZIP2	B-Application
compression	B-General_Concept
,	O
strong	O
encryption	O
specification	O
and	O
others	O
were	O
published	O
by	O
PKWARE	O
a	O
few	O
years	O
after	O
their	O
creation	O
.	O
</s>
<s>
2.0	O
:	O
(	O
1993	O
)	O
File	O
entries	O
can	O
be	O
compressed	O
with	O
DEFLATE	B-Algorithm
and	O
use	O
traditional	O
PKWARE	O
encryption	O
(	O
ZipCrypto	O
)	O
.	O
</s>
<s>
4.5	O
:	O
(	O
2001	O
)	O
Documented	O
64-bit	O
zip	B-Application
format	O
.	O
</s>
<s>
5.2	O
:	O
(	O
2003	O
)	O
AES	B-Algorithm
encryption	I-Algorithm
support	O
for	O
SES	O
(	O
defined	O
in	O
APPNOTE	O
5.1	O
that	O
was	O
not	O
published	O
online	O
)	O
and	O
AES	B-Algorithm
from	O
WinZip	B-Application
(	O
"	O
AE-x	O
"	O
)	O
;	O
corrected	O
version	O
of	O
RC2-64	O
supported	O
for	O
SES	O
encryption	O
.	O
</s>
<s>
Expanded	O
list	O
of	O
supported	O
compression	B-General_Concept
algorithms	I-General_Concept
(	O
LZMA	B-General_Concept
,	O
PPMd+	B-Algorithm
)	O
,	O
encryption	O
algorithms	O
(	O
Blowfish	B-Algorithm
,	O
Twofish	B-Algorithm
)	O
,	O
and	O
hashes	O
.	O
</s>
<s>
6.3.2	O
:	O
(	O
2007	O
)	O
Documented	O
compression	B-General_Concept
method	O
97	O
(	O
WavPack	B-Application
)	O
.	O
</s>
<s>
6.3.5	O
:	O
(	O
2018	O
)	O
Documented	O
compression	B-General_Concept
methods	O
16	O
,	O
96	O
and	O
99	O
,	O
DOS	O
timestamp	O
epoch	O
and	O
precision	O
,	O
added	O
extra	O
fields	O
for	O
keys	O
and	O
decryption	O
,	O
as	O
well	O
as	O
typos	O
and	O
clarifications	O
.	O
</s>
<s>
6.3.7	O
:	O
(	O
2020	O
)	O
Added	O
Zstandard	B-Language
compression	B-General_Concept
method	O
ID	O
20	O
.	O
</s>
<s>
6.3.8	O
:	O
(	O
2020	O
)	O
Moved	O
Zstandard	B-Language
compression	B-General_Concept
method	O
ID	O
from	O
20	O
to	O
93	O
,	O
deprecating	O
the	O
former	O
.	O
</s>
<s>
Documented	O
method	O
IDs	O
94	O
and	O
95	O
(	O
MP3	B-Application
and	O
XZ	B-Language
respectively	O
)	O
.	O
</s>
<s>
6.3.10	O
:	O
(	O
2022	O
)	O
Added	O
several	O
z/OS	B-Application
attribute	O
values	O
for	O
APPENDIX	O
B	O
.	O
</s>
<s>
WinZip	B-Application
,	O
starting	O
with	O
version	O
12.1	O
,	O
uses	O
the	O
extension	O
for	O
ZIP	B-General_Concept
files	I-General_Concept
that	O
use	O
compression	B-General_Concept
methods	O
newer	O
than	O
DEFLATE	B-Algorithm
;	O
specifically	O
,	O
methods	O
BZip	B-Application
,	O
LZMA	B-General_Concept
,	O
PPMd	B-Algorithm
,	O
Jpeg	O
and	O
Wavpack	B-Application
.	O
</s>
<s>
The	O
last	O
2	O
are	O
applied	O
to	O
appropriate	O
file	O
types	O
when	O
"	O
Best	O
method	O
"	O
compression	B-General_Concept
is	O
selected	O
.	O
</s>
<s>
In	O
April	O
2010	O
,	O
ISO/IEC	O
JTC	O
1	O
initiated	O
a	O
ballot	O
to	O
determine	O
whether	O
a	O
project	O
should	O
be	O
initiated	O
to	O
create	O
an	O
ISO/IEC	O
International	O
Standard	O
format	O
compatible	O
with	O
ZIP	B-Application
.	O
</s>
<s>
The	O
proposed	O
project	O
,	O
entitled	O
Document	O
Packaging	O
,	O
envisaged	O
a	O
ZIP-compatible	O
'	O
minimal	O
compressed	O
archive	O
format	O
 '	O
suitable	O
for	O
use	O
with	O
a	O
number	O
of	O
existing	O
standards	O
including	O
OpenDocument	B-Application
,	O
Office	B-Operating_System
Open	I-Operating_System
XML	I-Operating_System
and	O
EPUB	O
.	O
</s>
<s>
In	O
2015	O
,	O
ISO/IEC	O
21320-1	O
"	O
Document	O
Container	O
File	O
—	O
Part	O
1	O
:	O
Core	O
"	O
was	O
published	O
which	O
states	O
that	O
"	O
Document	O
container	O
files	O
are	O
conforming	O
Zip	B-General_Concept
files	I-General_Concept
"	O
.	O
</s>
<s>
It	O
requires	O
the	O
following	O
main	O
restrictions	O
of	O
the	O
ZIP	B-General_Concept
file	I-General_Concept
format	I-General_Concept
:	O
</s>
<s>
Files	O
in	O
ZIP	B-General_Concept
archives	I-General_Concept
may	O
only	O
be	O
stored	O
uncompressed	B-General_Concept
,	O
or	O
using	O
the	O
"	O
deflate	B-Algorithm
"	O
compression	B-General_Concept
(	O
i.e.	O
</s>
<s>
compression	B-General_Concept
method	O
may	O
contain	O
the	O
value	O
"	O
0	O
"	O
-	O
stored	O
or	O
"	O
8	B-Device
"	I-Device
-	O
deflated	O
)	O
.	O
</s>
<s>
ZIP	B-Application
allows	O
contained	O
files	O
to	O
be	O
compressed	O
using	O
many	O
different	O
methods	O
,	O
as	O
well	O
as	O
simply	O
storing	O
a	O
file	O
without	O
compressing	O
it	O
.	O
</s>
<s>
Because	O
the	O
files	O
in	O
a	O
ZIP	B-General_Concept
archive	I-General_Concept
are	O
compressed	O
individually	O
,	O
it	O
is	O
possible	O
to	O
extract	O
them	O
,	O
or	O
add	O
new	O
ones	O
,	O
without	O
applying	O
compression	B-General_Concept
or	O
decompression	O
to	O
the	O
entire	O
archive	O
.	O
</s>
<s>
This	O
contrasts	O
with	O
the	O
format	O
of	O
compressed	O
tar	B-Application
files	I-Application
,	O
for	O
which	O
such	O
random-access	O
processing	O
is	O
not	O
easily	O
possible	O
.	O
</s>
<s>
A	O
directory	O
is	O
placed	O
at	O
the	O
end	O
of	O
a	O
ZIP	B-General_Concept
file	I-General_Concept
.	O
</s>
<s>
This	O
identifies	O
what	O
files	O
are	O
in	O
the	O
ZIP	B-Application
and	O
identifies	O
where	O
in	O
the	O
ZIP	B-Application
that	O
file	O
is	O
located	O
.	O
</s>
<s>
This	O
allows	O
ZIP	B-Application
readers	O
to	O
load	O
the	O
list	O
of	O
files	O
without	O
reading	O
the	O
entire	O
ZIP	B-General_Concept
archive	I-General_Concept
.	O
</s>
<s>
ZIP	B-General_Concept
archives	I-General_Concept
can	O
also	O
include	O
extra	O
data	O
that	O
is	O
not	O
related	O
to	O
the	O
ZIP	B-General_Concept
archive	I-General_Concept
.	O
</s>
<s>
This	O
allows	O
for	O
a	O
ZIP	B-General_Concept
archive	I-General_Concept
to	O
be	O
made	O
into	O
a	O
self-extracting	B-General_Concept
archive	I-General_Concept
(	O
application	O
that	O
decompresses	O
its	O
contained	O
data	O
)	O
,	O
by	O
prepending	O
the	O
program	O
code	O
to	O
a	O
ZIP	B-General_Concept
archive	I-General_Concept
and	O
marking	O
the	O
file	O
as	O
executable	O
.	O
</s>
<s>
Storing	O
the	O
catalog	O
at	O
the	O
end	O
also	O
makes	O
possible	O
hiding	O
a	O
zipped	B-General_Concept
file	I-General_Concept
by	O
appending	O
it	O
to	O
an	O
innocuous	O
file	O
,	O
such	O
as	O
a	O
GIF	O
image	O
file	O
.	O
</s>
<s>
A	O
ZIP	B-General_Concept
file	I-General_Concept
is	O
correctly	O
identified	O
by	O
the	O
presence	O
of	O
an	O
end	O
of	O
central	O
directory	O
record	O
which	O
is	O
located	O
at	O
the	O
end	O
of	O
the	O
archive	O
structure	O
in	O
order	O
to	O
allow	O
the	O
easy	O
appending	O
of	O
new	O
files	O
.	O
</s>
<s>
If	O
the	O
end	O
of	O
central	O
directory	O
record	O
indicates	O
a	O
non-empty	O
archive	O
,	O
the	O
name	O
of	O
each	O
file	O
or	O
directory	O
within	O
the	O
archive	O
should	O
be	O
specified	O
in	O
a	O
central	O
directory	O
entry	O
,	O
along	O
with	O
other	O
metadata	O
about	O
the	O
entry	O
,	O
and	O
an	O
offset	O
into	O
the	O
ZIP	B-General_Concept
file	I-General_Concept
,	O
pointing	O
to	O
the	O
actual	O
entry	O
data	O
.	O
</s>
<s>
The	O
entries	O
within	O
the	O
ZIP	B-General_Concept
file	I-General_Concept
also	O
include	O
this	O
information	O
,	O
for	O
redundancy	O
,	O
in	O
a	O
local	O
file	O
header	O
.	O
</s>
<s>
Because	O
ZIP	B-General_Concept
files	I-General_Concept
may	O
be	O
appended	O
to	O
,	O
only	O
files	O
specified	O
in	O
the	O
central	O
directory	O
at	O
the	O
end	O
of	O
the	O
file	O
are	O
valid	O
.	O
</s>
<s>
Scanning	O
a	O
ZIP	B-General_Concept
file	I-General_Concept
for	O
local	O
file	O
headers	O
is	O
invalid	O
(	O
except	O
in	O
the	O
case	O
of	O
corrupted	O
archives	O
)	O
,	O
as	O
the	O
central	O
directory	O
may	O
declare	O
that	O
some	O
files	O
have	O
been	O
deleted	O
and	O
other	O
files	O
have	O
been	O
updated	O
.	O
</s>
<s>
For	O
example	O
,	O
we	O
may	O
start	O
with	O
a	O
ZIP	B-General_Concept
file	I-General_Concept
that	O
contains	O
files	O
A	O
,	O
B	O
and	O
C	O
.	O
File	O
B	O
is	O
then	O
deleted	O
and	O
C	O
updated	O
.	O
</s>
<s>
This	O
may	O
be	O
achieved	O
by	O
just	O
appending	O
a	O
new	O
file	O
C	O
to	O
the	O
end	O
of	O
the	O
original	O
ZIP	B-General_Concept
file	I-General_Concept
and	O
adding	O
a	O
new	O
central	O
directory	O
that	O
only	O
lists	O
file	O
A	O
and	O
the	O
new	O
file	O
C	O
.	O
When	O
ZIP	B-Application
was	O
first	O
designed	O
,	O
transferring	O
files	O
by	O
floppy	B-Device
disk	I-Device
was	O
common	O
,	O
yet	O
writing	O
to	O
disks	O
was	O
very	O
time-consuming	O
.	O
</s>
<s>
If	O
you	O
had	O
a	O
large	O
zip	B-General_Concept
file	I-General_Concept
,	O
possibly	O
spanning	O
multiple	O
disks	O
,	O
and	O
only	O
needed	O
to	O
update	O
a	O
few	O
files	O
,	O
rather	O
than	O
reading	O
and	O
re-writing	O
all	O
the	O
files	O
,	O
it	O
would	O
be	O
substantially	O
faster	O
to	O
just	O
read	O
the	O
old	O
central	O
directory	O
,	O
append	O
the	O
new	O
files	O
then	O
append	O
an	O
updated	O
central	O
directory	O
.	O
</s>
<s>
Each	O
entry	O
stored	O
in	O
a	O
ZIP	B-General_Concept
archive	I-General_Concept
is	O
introduced	O
by	O
a	O
local	O
file	O
header	O
with	O
information	O
about	O
the	O
file	O
such	O
as	O
the	O
comment	O
,	O
file	O
size	O
and	O
file	O
name	O
,	O
followed	O
by	O
optional	O
"	O
extra	O
"	O
data	O
fields	O
,	O
and	O
then	O
the	O
possibly	O
compressed	O
,	O
possibly	O
encrypted	O
file	O
data	O
.	O
</s>
<s>
The	O
"	O
Extra	O
"	O
data	O
fields	O
are	O
the	O
key	O
to	O
the	O
extensibility	O
of	O
the	O
ZIP	B-Application
format	O
.	O
</s>
<s>
"	O
Extra	O
"	O
fields	O
are	O
exploited	O
to	O
support	O
the	O
ZIP64	O
format	O
,	O
WinZip-compatible	O
AES	B-Algorithm
encryption	I-Algorithm
,	O
file	O
attributes	O
,	O
and	O
higher-resolution	O
NTFS	B-Application
or	O
Unix	O
file	O
timestamps	O
.	O
</s>
<s>
ZIP	B-Application
tools	O
are	O
required	O
by	O
the	O
specification	O
to	O
ignore	O
Extra	O
fields	O
they	O
do	O
not	O
recognize	O
.	O
</s>
<s>
The	O
ZIP	B-Application
format	O
uses	O
specific	O
4-byte	O
"	O
signatures	O
"	O
to	O
denote	O
the	O
various	O
structures	O
in	O
the	O
file	O
.	O
</s>
<s>
There	O
is	O
no	O
BOF	O
or	O
EOF	O
marker	O
in	O
the	O
ZIP	B-Application
specification	O
.	O
</s>
<s>
Conventionally	O
the	O
first	O
thing	O
in	O
a	O
ZIP	B-General_Concept
file	I-General_Concept
is	O
a	O
ZIP	B-Application
entry	O
,	O
which	O
can	O
be	O
identified	O
easily	O
by	O
its	O
local	O
file	O
header	O
signature	O
.	O
</s>
<s>
However	O
,	O
this	O
is	O
not	O
necessarily	O
the	O
case	O
,	O
as	O
this	O
is	O
not	O
required	O
by	O
the	O
ZIP	B-Application
specification	O
-	O
most	O
notably	O
,	O
a	O
self-extracting	B-General_Concept
archive	I-General_Concept
will	O
begin	O
with	O
an	O
executable	O
file	O
header	O
.	O
</s>
<s>
Tools	O
that	O
correctly	O
read	O
ZIP	B-General_Concept
archives	I-General_Concept
must	O
scan	O
for	O
the	O
end	O
of	O
central	O
directory	O
record	O
signature	O
,	O
and	O
then	O
,	O
as	O
appropriate	O
,	O
the	O
other	O
,	O
indicated	O
,	O
central	O
directory	O
records	O
.	O
</s>
<s>
They	O
must	O
not	O
scan	O
for	O
entries	O
from	O
the	O
top	O
of	O
the	O
ZIP	B-General_Concept
file	I-General_Concept
,	O
because	O
(	O
as	O
previously	O
mentioned	O
in	O
this	O
section	O
)	O
only	O
the	O
central	O
directory	O
specifies	O
where	O
a	O
file	O
chunk	O
starts	O
and	O
that	O
it	O
has	O
not	O
been	O
deleted	O
.	O
</s>
<s>
However	O
,	O
tools	O
that	O
attempt	O
to	O
recover	O
data	O
from	O
damaged	O
ZIP	B-Application
archives	O
will	O
most	O
likely	O
scan	O
the	O
archive	O
for	O
local	O
file	O
header	O
signatures	O
;	O
this	O
is	O
made	O
more	O
difficult	O
by	O
the	O
fact	O
that	O
the	O
compressed	O
size	O
of	O
a	O
file	O
chunk	O
may	O
be	O
stored	O
after	O
the	O
file	O
chunk	O
,	O
making	O
sequential	O
processing	O
difficult	O
.	O
</s>
<s>
Viewed	O
as	O
an	O
ASCII	B-Protocol
string	O
this	O
reads	O
"	O
PK	O
"	O
,	O
the	O
initials	O
of	O
the	O
inventor	O
Phil	O
Katz	O
.	O
</s>
<s>
Thus	O
,	O
when	O
a	O
ZIP	B-General_Concept
file	I-General_Concept
is	O
viewed	O
in	O
a	O
text	O
editor	O
the	O
first	O
two	O
bytes	O
of	O
the	O
file	O
are	O
usually	O
"	O
PK	O
"	O
.	O
</s>
<s>
(	O
DOS	O
,	O
OS/2	O
and	O
Windows	O
self-extracting	O
ZIPs	B-Application
have	O
an	O
EXE	O
before	O
the	O
ZIP	B-Application
so	O
start	O
with	O
"	O
MZ	O
"	O
;	O
self-extracting	O
ZIPs	B-Application
for	O
other	O
operating	O
systems	O
may	O
similarly	O
be	O
preceded	O
by	O
executable	O
code	O
for	O
extracting	O
the	O
archive	O
's	O
content	O
on	O
that	O
platform	O
.	O
)	O
</s>
<s>
The	O
specification	O
also	O
supports	O
spreading	O
archives	O
across	O
multiple	O
file-system	B-Application
files	O
.	O
</s>
<s>
Originally	O
intended	O
for	O
storage	O
of	O
large	O
ZIP	B-General_Concept
files	I-General_Concept
across	O
multiple	O
floppy	B-Device
disks	I-Device
,	O
this	O
feature	O
is	O
now	O
used	O
for	O
sending	O
ZIP	B-General_Concept
archives	I-General_Concept
in	O
parts	O
over	O
email	O
,	O
or	O
over	O
other	O
transports	O
or	O
removable	O
media	O
.	O
</s>
<s>
The	O
FAT	B-Application
filesystem	I-Application
of	O
DOS	O
has	O
a	O
timestamp	O
resolution	O
of	O
only	O
two	O
seconds	O
;	O
ZIP	B-General_Concept
file	I-General_Concept
records	O
mimic	O
this	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
the	O
built-in	O
timestamp	O
resolution	O
of	O
files	O
in	O
a	O
ZIP	B-General_Concept
archive	I-General_Concept
is	O
only	O
two	O
seconds	O
,	O
though	O
extra	O
fields	O
can	O
be	O
used	O
to	O
store	O
more	O
precise	O
timestamps	O
.	O
</s>
<s>
The	O
ZIP	B-Application
format	O
has	O
no	O
notion	O
of	O
time	B-Device
zone	I-Device
,	O
so	O
timestamps	O
are	O
only	O
meaningful	O
if	O
it	O
is	O
known	O
what	O
time	B-Device
zone	I-Device
they	O
were	O
created	O
in	O
.	O
</s>
<s>
In	O
September	O
2006	O
,	O
PKWARE	O
released	O
a	O
revision	O
of	O
the	O
ZIP	B-Application
specification	O
providing	O
for	O
the	O
storage	O
of	O
file	O
names	O
using	O
UTF-8	O
,	O
finally	O
adding	O
Unicode	O
compatibility	O
to	O
ZIP	B-Application
.	O
</s>
<s>
+	O
Local	O
file	O
header	O
Offset	O
Bytes	O
Description	O
0	O
4	O
Local	O
file	O
header	O
signature	O
=	O
0x04034b50	O
(	O
PK	O
♥	O
♦	O
or	O
"	O
PK	O
\3\4	O
 "	O
)	O
4	O
2	O
Version	O
needed	O
to	O
extract	O
(	O
minimum	O
)	O
6	O
2	O
General	O
purpose	O
bit	O
flag	O
8	O
2	O
Compression	B-General_Concept
method	O
;	O
e.g.	O
</s>
<s>
A	O
ZIP64	O
local	O
file	O
extra	O
field	O
record	O
,	O
for	O
example	O
,	O
has	O
the	O
signature	O
0x0001	O
and	O
a	O
length	O
of	O
16	O
bytes	O
(	O
or	O
more	O
)	O
so	O
that	O
two	O
64-bit	O
values	O
(	O
the	O
uncompressed	B-General_Concept
and	O
compressed	O
sizes	O
)	O
may	O
follow	O
.	O
</s>
<s>
This	O
is	O
immediately	O
followed	O
by	O
the	O
compressed	B-General_Concept
data	I-General_Concept
.	O
</s>
<s>
If	O
the	O
archive	O
is	O
in	O
Zip64	O
format	O
,	O
the	O
compressed	O
and	O
uncompressed	B-General_Concept
size	O
fields	O
are	O
8	O
bytes	O
long	O
instead	O
of	O
4	O
bytes	O
long	O
(	O
see	O
section	O
4.3.9.2	O
)	O
.	O
</s>
<s>
The	O
equivalent	O
fields	O
in	O
the	O
local	O
header	O
(	O
or	O
in	O
the	O
Zip64	O
extended	O
information	O
extra	O
field	O
in	O
the	O
case	O
of	O
archives	O
in	O
Zip64	O
format	O
)	O
are	O
filled	O
with	O
zero	O
,	O
and	O
the	O
CRC-32	O
and	O
size	O
are	O
appended	O
in	O
a	O
12-byte	O
structure	O
(	O
optionally	O
preceded	O
by	O
a	O
4-byte	O
signature	O
)	O
immediately	O
after	O
the	O
compressed	B-General_Concept
data	I-General_Concept
:	O
</s>
<s>
+	O
Central	O
directory	O
file	O
header	O
Offset	O
Bytes	O
Description	O
0	O
4	O
Central	O
directory	O
file	O
header	O
signature	O
=	O
0x02014b50	O
4	O
2	O
Version	O
made	O
by	O
6	O
2	O
Version	O
needed	O
to	O
extract	O
(	O
minimum	O
)	O
8	O
2	O
General	O
purpose	O
bit	O
flag	O
10	O
2	O
Compression	B-General_Concept
method	O
12	O
2	O
File	O
last	O
modification	O
time	O
14	O
2	O
File	O
last	O
modification	O
date	O
16	O
4	O
CRC-32	O
of	O
uncompressed	B-General_Concept
data	O
20	O
4	O
Compressed	O
size	O
(	O
or	O
0xffffffff	O
for	O
ZIP64	O
)	O
24	O
4	O
Uncompressed	B-General_Concept
size	O
(	O
or	O
0xffffffff	O
for	O
ZIP64	O
)	O
28	O
2	O
File	O
name	O
length	O
(	O
n	O
)	O
30	O
2	O
Extra	O
field	O
length	O
(	O
m	O
)	O
32	O
2	O
File	O
comment	O
length	O
(	O
k	O
)	O
34	O
2	O
Disk	O
number	O
where	O
file	O
starts	O
(	O
or	O
0xffff	O
for	O
ZIP64	O
)	O
36	O
2	O
Internal	O
file	O
attributes	O
38	O
4	O
External	O
file	O
attributes	O
42	O
4	O
Relative	O
offset	O
of	O
local	O
file	O
header	O
(	O
or	O
0xffffffff	O
for	O
ZIP64	O
)	O
.	O
</s>
<s>
This	O
allows	O
software	O
reading	O
the	O
central	O
directory	O
to	O
locate	O
the	O
position	O
of	O
the	O
file	O
inside	O
the	O
ZIP	B-General_Concept
file	I-General_Concept
.	O
</s>
<s>
After	O
all	O
the	O
central	O
directory	O
entries	O
comes	O
the	O
end	O
of	O
central	O
directory	O
(	O
EOCD	B-General_Concept
)	O
record	O
,	O
which	O
marks	O
the	O
end	O
of	O
the	O
ZIP	B-General_Concept
file	I-General_Concept
:	O
</s>
<s>
This	O
ordering	O
allows	O
a	O
ZIP	B-General_Concept
file	I-General_Concept
to	O
be	O
created	O
in	O
one	O
pass	O
,	O
but	O
the	O
central	O
directory	O
is	O
also	O
placed	O
at	O
the	O
end	O
of	O
the	O
file	O
in	O
order	O
to	O
facilitate	O
easy	O
removal	O
of	O
files	O
from	O
multiple-part	O
(	O
e.g.	O
</s>
<s>
"	O
multiple	O
floppy-disk	O
"	O
)	O
archives	O
,	O
as	O
previously	O
discussed	O
.	O
</s>
<s>
The	O
.ZIP	B-General_Concept
File	I-General_Concept
Format	O
Specification	O
documents	O
the	O
following	O
compression	B-General_Concept
methods	O
:	O
Store	O
(	O
no	O
compression	B-General_Concept
)	O
,	O
Shrink	O
(	O
LZW	B-Algorithm
)	O
,	O
Reduce	O
(	O
levels	O
1	O
–	O
4	O
;	O
LZ77	O
+	O
probabilistic	O
)	O
,	O
Implode	O
,	O
Deflate	B-Algorithm
,	O
Deflate64	O
,	O
bzip2	B-Application
,	O
LZMA	B-General_Concept
,	O
WavPack	B-Application
,	O
PPMd	B-Algorithm
,	O
and	O
a	O
LZ77	O
variant	O
provided	O
by	O
IBM	B-Application
z/OS	I-Application
CMPSC	O
instruction	O
.	O
</s>
<s>
The	O
most	O
commonly	O
used	O
compression	B-General_Concept
method	O
is	O
DEFLATE	B-Algorithm
,	O
which	O
is	O
described	O
in	O
IETF	O
.	O
</s>
<s>
Other	O
methods	O
mentioned	O
,	O
but	O
not	O
documented	O
in	O
detail	O
in	O
the	O
specification	O
include	O
:	O
PKWARE	O
DCL	O
Implode	O
(	O
old	O
IBM	B-Application
TERSE	I-Application
)	O
,	O
new	O
IBM	B-Application
TERSE	I-Application
,	O
IBM	O
LZ77	O
z	O
Architecture	O
(	O
PFS	O
)	O
,	O
and	O
a	O
JPEG	O
variant	O
.	O
</s>
<s>
The	O
word	O
Implode	O
is	O
overused	O
by	O
PKWARE	O
:	O
the	O
DCL/TERSE	O
Implode	O
is	O
distinct	O
from	O
the	O
old	O
PKZIP	B-Application
Implode	O
,	O
a	O
predecessor	O
to	O
Deflate	B-Algorithm
.	O
</s>
<s>
The	O
DCL	O
Implode	O
is	O
undocumented	O
partially	O
due	O
to	O
its	O
proprietary	B-Application
nature	O
held	O
by	O
IBM	O
,	O
but	O
Mark	O
Adler	O
has	O
nevertheless	O
provided	O
a	O
decompressor	O
called	O
"	O
blast	O
"	O
alongside	O
zlib	B-Language
.	O
</s>
<s>
ZIP	B-Application
supports	O
a	O
simple	O
password-based	O
symmetric	B-Algorithm
encryption	I-Algorithm
system	O
generally	O
known	O
as	O
ZipCrypto	O
.	O
</s>
<s>
It	O
is	O
documented	O
in	O
the	O
ZIP	B-Application
specification	O
,	O
and	O
known	O
to	O
be	O
seriously	O
flawed	O
.	O
</s>
<s>
Computers	O
running	O
under	O
native	O
Microsoft	B-Application
Windows	I-Application
without	O
third-party	O
archivers	O
can	O
open	O
,	O
but	O
not	O
create	O
,	O
ZIP	B-General_Concept
files	I-General_Concept
encrypted	O
with	O
ZipCrypto	O
,	O
but	O
cannot	O
extract	O
the	O
contents	O
of	O
files	O
using	O
different	O
encryption	O
.	O
</s>
<s>
New	O
features	O
including	O
new	O
compression	B-General_Concept
and	O
encryption	O
(	O
e.g.	O
</s>
<s>
AES	B-Algorithm
)	O
methods	O
have	O
been	O
documented	O
in	O
the	O
ZIP	B-General_Concept
File	I-General_Concept
Format	I-General_Concept
Specification	O
since	O
version	O
5.2	O
.	O
</s>
<s>
A	O
WinZip-developed	O
AES-based	O
open	O
standard	O
(	O
"	O
AE-x	O
"	O
in	O
APPNOTE	O
)	O
is	O
used	O
also	O
by	O
7-Zip	B-Language
and	O
Xceed	O
,	O
but	O
some	O
vendors	O
use	O
other	O
formats	O
.	O
</s>
<s>
PKWARE	O
SecureZIP	B-Application
(	O
SES	O
,	O
proprietary	B-Application
)	O
also	O
supports	O
RC2	B-Algorithm
,	O
RC4	B-Algorithm
,	O
DES	B-Algorithm
,	O
Triple	B-Algorithm
DES	I-Algorithm
encryption	O
methods	O
,	O
Digital	O
Certificate-based	O
encryption	O
and	O
authentication	O
(	O
X.509	O
)	O
,	O
and	O
archive	O
header	O
encryption	O
.	O
</s>
<s>
File	O
name	O
encryption	O
is	O
introduced	O
in	O
.ZIP	B-General_Concept
File	I-General_Concept
Format	O
Specification	O
6.2	O
,	O
which	O
encrypts	O
metadata	O
stored	O
in	O
Central	O
Directory	O
portion	O
of	O
an	O
archive	O
,	O
but	O
Local	O
Header	O
sections	O
remain	O
unencrypted	O
.	O
</s>
<s>
As	O
of	O
version	O
6.2	O
of	O
the	O
specification	O
,	O
the	O
Compression	B-General_Concept
Method	O
and	O
Compressed	O
Size	O
fields	O
within	O
Local	O
Header	O
are	O
not	O
yet	O
masked	O
.	O
</s>
<s>
The	O
original	O
format	O
had	O
a	O
4GB	O
(	O
232	O
bytes	O
)	O
limit	O
on	O
various	O
things	O
(	O
uncompressed	B-General_Concept
size	O
of	O
a	O
file	O
,	O
compressed	O
size	O
of	O
a	O
file	O
,	O
and	O
total	O
size	O
of	O
the	O
archive	O
)	O
,	O
as	O
well	O
as	O
a	O
limit	O
of	O
65,535	O
(	O
216-1	O
)	O
entries	O
in	O
a	O
ZIP	B-General_Concept
archive	I-General_Concept
.	O
</s>
<s>
The	O
format	O
of	O
the	O
Local	O
file	O
header	O
(	O
LOC	O
)	O
and	O
Central	O
directory	O
entry	O
(	O
CEN	O
)	O
are	O
the	O
same	O
in	O
ZIP	B-Application
and	O
ZIP64	O
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
the	O
format	O
of	O
EOCD	B-General_Concept
for	O
ZIP64	O
is	O
slightly	O
different	O
from	O
the	O
normal	O
ZIP	B-Application
version	O
.	O
</s>
<s>
Likewise	O
,	O
some	O
extension	O
libraries	O
support	O
ZIP64	O
,	O
such	O
as	O
DotNetZip	O
,	O
QuaZIP	O
and	O
IO::Compress::Zip	O
in	O
Perl	O
.	O
</s>
<s>
Python	B-Language
's	O
built-in	O
zipfile	B-General_Concept
supports	O
it	O
since	O
2.5	O
and	O
defaults	O
to	O
it	O
since	O
3.4	O
.	O
</s>
<s>
OpenJDK	B-Language
's	O
built-in	O
java.util.zip	O
supports	O
ZIP64	O
from	O
version	O
Java	O
7	O
.	O
</s>
<s>
Android	B-Application
Java	O
API	O
support	O
ZIP64	O
since	O
Android	B-Application
6.0	O
.	O
</s>
<s>
Mac	B-Application
OS	I-Application
Sierra	O
's	O
Archive	O
Utility	O
notably	O
does	O
not	O
support	O
ZIP64	O
,	O
and	O
can	O
create	O
corrupt	O
archives	O
when	O
ZIP64	O
would	O
be	O
required	O
.	O
</s>
<s>
However	O
,	O
the	O
ditto	O
command	O
shipped	O
with	O
Mac	B-Application
OS	I-Application
will	O
unzip	B-General_Concept
ZIP64	O
files	O
.	O
</s>
<s>
More	O
recent	O
versions	O
of	O
Mac	B-Application
OS	I-Application
ship	O
with	O
info-zip	B-Application
'	O
s	O
zip	B-Application
and	O
unzip	B-General_Concept
command	O
line	O
tools	O
which	O
do	O
support	O
Zip64	O
:	O
to	O
verify	O
run	O
zip	B-Application
-v	O
and	O
look	O
for	O
"	O
ZIP64_SUPPORT	O
"	O
.	O
</s>
<s>
Also	O
,	O
because	O
the	O
central	O
directory	O
specifies	O
the	O
offset	O
of	O
each	O
file	O
in	O
the	O
archive	O
with	O
respect	O
to	O
the	O
start	O
,	O
it	O
is	O
possible	O
for	O
the	O
first	O
file	O
entry	O
to	O
start	O
at	O
an	O
offset	O
other	O
than	O
zero	O
,	O
although	O
some	O
tools	O
,	O
for	O
example	O
gzip	B-Application
,	O
will	O
not	O
process	O
archive	O
files	O
that	O
do	O
not	O
start	O
with	O
a	O
file	O
entry	O
at	O
offset	O
zero	O
.	O
</s>
<s>
This	O
allows	O
arbitrary	O
data	O
to	O
occur	O
in	O
the	O
file	O
both	O
before	O
and	O
after	O
the	O
ZIP	B-General_Concept
archive	I-General_Concept
data	O
,	O
and	O
for	O
the	O
archive	O
to	O
still	O
be	O
read	O
by	O
a	O
ZIP	B-Application
application	O
.	O
</s>
<s>
A	O
side-effect	O
of	O
this	O
is	O
that	O
it	O
is	O
possible	O
to	O
author	O
a	O
file	O
that	O
is	O
both	O
a	O
working	O
ZIP	B-General_Concept
archive	I-General_Concept
and	O
another	O
format	O
,	O
provided	O
that	O
the	O
other	O
format	O
tolerates	O
arbitrary	O
data	O
at	O
its	O
end	O
,	O
beginning	O
,	O
or	O
middle	O
.	O
</s>
<s>
Self-extracting	B-General_Concept
archives	I-General_Concept
(	O
SFX	O
)	O
,	O
of	O
the	O
form	O
supported	O
by	O
WinZip	B-Application
,	O
take	O
advantage	O
of	O
this	O
,	O
in	O
that	O
they	O
are	O
executable	O
(	O
)	O
files	O
that	O
conform	O
to	O
the	O
PKZIP	B-Application
AppNote.txt	O
specification	O
,	O
and	O
can	O
be	O
read	O
by	O
compliant	O
zip	B-Application
tools	O
or	O
libraries	O
.	O
</s>
<s>
This	O
property	O
of	O
the	O
format	O
,	O
and	O
of	O
the	O
JAR	B-Language
format	O
which	O
is	O
a	O
variant	O
of	O
ZIP	B-Application
,	O
can	O
be	O
exploited	O
to	O
hide	O
rogue	O
content	O
(	O
such	O
as	O
harmful	O
Java	O
classes	O
)	O
inside	O
a	O
seemingly	O
harmless	O
file	O
,	O
such	O
as	O
a	O
GIF	O
image	O
uploaded	O
to	O
the	O
web	O
.	O
</s>
<s>
Such	O
an	O
empty	O
zip	B-General_Concept
file	I-General_Concept
contains	O
only	O
an	O
End	O
of	O
Central	O
Directory	O
Record	O
(	O
EOCD	B-General_Concept
)	O
:	O
</s>
<s>
The	O
maximum	O
size	O
for	O
both	O
the	O
archive	O
file	O
and	O
the	O
individual	O
files	O
inside	O
it	O
is	O
4,294,967,295	O
bytes	O
(	O
232−1	O
bytes	O
,	O
or	O
4GB	O
minus	O
1	O
byte	O
)	O
for	O
standard	O
ZIP	B-Application
.	O
</s>
<s>
A	O
Seek-Optimized	O
ZIP	B-General_Concept
file	I-General_Concept
(	O
SOZip	O
)	O
profile	O
has	O
been	O
proposed	O
for	O
the	O
ZIP	B-Application
format	O
.	O
</s>
<s>
Such	O
file	O
contains	O
one	O
or	O
several	O
Deflate-compressed	O
files	O
that	O
are	O
organized	O
and	O
annotated	O
such	O
that	O
a	O
SOZip-aware	O
reader	O
can	O
perform	O
very	O
fast	O
random	O
access	O
(	O
seek	O
)	O
within	O
a	O
compressed	O
file	O
.	O
</s>
<s>
SOZip	O
makes	O
it	O
possible	O
to	O
access	O
large	O
compressed	O
files	O
directly	O
from	O
a	O
.zip	B-General_Concept
file	I-General_Concept
without	O
prior	O
decompression	O
.	O
</s>
<s>
It	O
combines	O
the	O
use	O
of	O
ZLib	B-Language
block	O
flushs	O
issued	O
at	O
regular	O
interval	O
with	O
a	O
hidden	O
index	O
file	O
mapping	O
offsets	O
of	O
the	O
uncompressed	B-General_Concept
file	O
to	O
offsets	O
in	O
the	O
compressed	O
stream	O
.	O
</s>
<s>
ZIP	B-Application
readers	O
that	O
are	O
not	O
aware	O
of	O
that	O
extension	O
can	O
read	O
a	O
SOZip-enabled	O
file	O
normally	O
and	O
ignore	O
the	O
extended	O
features	O
that	O
support	O
efficient	O
seek	O
capability	O
.	O
</s>
<s>
file	O
format	O
includes	O
an	O
extra	O
field	O
facility	O
within	O
file	O
headers	O
,	O
which	O
can	O
be	O
used	O
to	O
store	O
extra	O
data	O
not	O
defined	O
by	O
existing	O
ZIP	B-Application
specifications	O
,	O
and	O
which	O
allow	O
compliant	O
archivers	O
that	O
do	O
not	O
recognize	O
the	O
fields	O
to	O
safely	O
skip	O
them	O
.	O
</s>
<s>
The	O
remaining	O
IDs	O
can	O
be	O
used	O
by	O
third-party	O
vendors	O
for	O
proprietary	B-Application
usage	O
.	O
</s>
<s>
When	O
WinZip	B-Application
9.0	O
public	O
beta	O
was	O
released	O
in	O
2003	O
,	O
WinZip	B-Application
introduced	O
its	O
own	O
AES-256	B-Algorithm
encryption	O
,	O
using	O
a	O
different	O
file	O
format	O
,	O
along	O
with	O
the	O
documentation	O
for	O
the	O
new	O
specification	O
.	O
</s>
<s>
The	O
encryption	O
standards	O
themselves	O
were	O
not	O
proprietary	B-Application
,	O
but	O
PKWARE	O
had	O
not	O
updated	O
APPNOTE.TXT	O
to	O
include	O
Strong	O
Encryption	O
Specification	O
(	O
SES	O
)	O
since	O
2001	O
,	O
which	O
had	O
been	O
used	O
by	O
PKZIP	B-Application
versions	O
5.0	O
and	O
6.0	O
.	O
</s>
<s>
WinZip	B-Application
technical	O
consultant	O
Kevin	O
Kearney	O
and	O
StuffIt	B-Application
product	O
manager	O
Mathew	O
Covington	O
accused	O
PKWARE	O
of	O
withholding	O
SES	O
,	O
but	O
PKZIP	B-Application
chief	O
technology	O
officer	O
Jim	O
Peterson	O
claimed	O
that	O
certificate-based	O
encryption	O
was	O
still	O
incomplete	O
.	O
</s>
<s>
In	O
another	O
controversial	O
move	O
,	O
PKWare	O
applied	O
for	O
a	O
patent	O
on	O
16	O
July	O
2003	O
describing	O
a	O
method	O
for	O
combining	O
ZIP	B-Application
and	O
strong	O
encryption	O
to	O
create	O
a	O
secure	O
file	O
.	O
</s>
<s>
In	O
the	O
end	O
,	O
PKWARE	O
and	O
WinZip	B-Application
agreed	O
to	O
support	O
each	O
other	O
's	O
products	O
.	O
</s>
<s>
On	O
21	O
January	O
2004	O
,	O
PKWARE	O
announced	O
the	O
support	O
of	O
WinZip-based	O
AES	B-Algorithm
compression	B-General_Concept
format	O
.	O
</s>
<s>
In	O
a	O
later	O
version	O
of	O
WinZip	B-Application
beta	O
,	O
it	O
was	O
able	O
to	O
support	O
SES-based	O
ZIP	B-General_Concept
files	I-General_Concept
.	O
</s>
<s>
PKWARE	O
eventually	O
released	O
version	O
5.2	O
of	O
the	O
.ZIP	B-General_Concept
File	I-General_Concept
Format	O
Specification	O
to	O
the	O
public	O
,	O
which	O
documented	O
SES	O
.	O
</s>
<s>
The	O
Free	B-Application
Software	I-Application
project	O
7-Zip	B-Language
also	O
supports	O
AES	B-Algorithm
,	O
but	O
not	O
SES	O
in	O
ZIP	B-General_Concept
files	I-General_Concept
(	O
as	O
does	O
its	O
POSIX	O
port	O
p7zip	B-Language
)	O
.	O
</s>
<s>
When	O
using	O
AES	B-Algorithm
encryption	I-Algorithm
under	O
WinZip	B-Application
,	O
the	O
compression	B-General_Concept
method	O
is	O
always	O
set	O
to	O
99	O
,	O
with	O
the	O
actual	O
compression	B-General_Concept
method	O
stored	O
in	O
an	O
AES	B-Algorithm
extra	O
data	O
field	O
.	O
</s>
<s>
In	O
contrast	O
,	O
Strong	O
Encryption	O
Specification	O
stores	O
the	O
compression	B-General_Concept
method	O
in	O
the	O
basic	O
file	O
header	O
segment	O
of	O
Local	O
Header	O
and	O
Central	O
Directory	O
,	O
unless	O
Central	O
Directory	O
Encryption	O
is	O
used	O
to	O
mask/encrypt	O
metadata	O
.	O
</s>
<s>
There	O
are	O
numerous	O
tools	O
available	O
,	O
and	O
numerous	O
libraries	O
for	O
various	O
programming	O
environments	O
;	O
licenses	O
used	O
include	O
proprietary	B-Application
and	O
free	B-Application
software	I-Application
.	O
</s>
<s>
WinZip	B-Application
,	O
WinRAR	B-Application
,	O
Info-ZIP	B-Application
,	O
ZipGenius	B-Application
,	O
7-Zip	B-Language
,	O
PeaZip	B-Application
and	O
B1	B-Application
Free	I-Application
Archiver	I-Application
are	O
well-known	O
tools	O
,	O
available	O
on	O
various	O
platforms	O
.	O
</s>
<s>
Some	O
development	O
libraries	O
licensed	O
under	O
open	O
source	O
agreement	O
are	O
libzip	B-Application
,	O
libarchive	O
,	O
and	O
Info-ZIP	B-Application
.	O
</s>
<s>
For	O
Java	O
:	O
Java	B-Language
Platform	I-Language
,	I-Language
Standard	I-Language
Edition	I-Language
contains	O
the	O
package	O
"	O
java.util.zip	O
"	O
to	O
handle	O
standard	O
files	O
;	O
the	O
Zip64File	O
library	O
specifically	O
supports	O
large	O
files	O
(	O
larger	O
than	O
4GB	O
)	O
and	O
treats	O
files	O
using	O
random	O
access	O
;	O
and	O
the	O
Apache	B-Application
Ant	I-Application
tool	O
contains	O
a	O
more	O
complete	O
implementation	O
released	O
under	O
the	O
Apache	B-Application
Software	I-Application
License	I-Application
.	O
</s>
<s>
The	O
Info-ZIP	B-Application
implementations	O
of	O
the	O
format	O
adds	O
support	O
for	O
Unix	O
filesystem	B-Application
features	O
,	O
such	O
as	O
user	O
and	O
group	O
IDs	O
,	O
file	O
permissions	O
,	O
and	O
support	O
for	O
symbolic	O
links	O
.	O
</s>
<s>
The	O
Apache	B-Application
Ant	I-Application
implementation	O
is	O
aware	O
of	O
these	O
to	O
the	O
extent	O
that	O
it	O
can	O
create	O
files	O
with	O
predefined	O
Unix	O
permissions	O
.	O
</s>
<s>
The	O
Info-ZIP	B-Application
implementations	O
also	O
know	O
how	O
to	O
use	O
the	O
error	O
correction	O
capabilities	O
built	O
into	O
the	O
compression	B-General_Concept
format	O
.	O
</s>
<s>
The	O
Info-ZIP	B-Application
Windows	O
tools	O
also	O
support	O
NTFS	B-Application
filesystem	B-Application
permissions	O
,	O
and	O
will	O
make	O
an	O
attempt	O
to	O
translate	O
from	O
NTFS	B-Application
permissions	O
to	O
Unix	O
permissions	O
or	O
vice	O
versa	O
when	O
extracting	O
files	O
.	O
</s>
<s>
.exe	O
files	O
being	O
created	O
on	O
NTFS	B-Application
volumes	O
with	O
executable	O
permission	O
denied	O
.	O
</s>
<s>
Versions	O
of	O
Microsoft	B-Application
Windows	I-Application
have	O
included	O
support	O
for	O
compression	B-General_Concept
in	O
Explorer	O
since	O
the	O
Microsoft	B-Application
Plus	I-Application
!	I-Application
</s>
<s>
Microsoft	O
calls	O
this	O
feature	O
"	O
Compressed	B-General_Concept
Folders	I-General_Concept
"	O
.	O
</s>
<s>
Not	O
all	O
features	O
are	O
supported	O
by	O
the	O
Windows	O
Compressed	B-General_Concept
Folders	I-General_Concept
capability	O
.	O
</s>
<s>
Unicode	O
entry	O
encoding	O
is	O
not	O
supported	O
until	O
Windows	B-Device
7	I-Device
,	O
while	O
split	O
and	O
spanned	O
archives	O
are	O
not	O
readable	O
or	O
writable	O
by	O
the	O
Compressed	B-General_Concept
Folders	I-General_Concept
feature	O
,	O
nor	O
is	O
AES	B-Algorithm
Encryption	I-Algorithm
supported	O
.	O
</s>
<s>
Microsoft	O
Office	O
started	O
using	O
the	O
zip	B-General_Concept
archive	I-General_Concept
format	O
in	O
2006	O
for	O
their	O
Office	B-Operating_System
Open	I-Operating_System
XML	I-Operating_System
.docx	O
,	O
.xlsx	B-Operating_System
,	O
.pptx	O
,	O
etc	O
.	O
</s>
<s>
files	O
,	O
which	O
became	O
the	O
default	O
file	O
format	O
with	O
Microsoft	B-Application
Office	I-Application
2007	I-Application
.	O
</s>
<s>
There	O
are	O
numerous	O
other	O
standards	O
and	O
formats	O
using	O
"	O
zip	B-Application
"	O
as	O
part	O
of	O
their	O
name	O
.	O
</s>
<s>
For	O
example	O
,	O
zip	B-Application
is	O
distinct	O
from	O
gzip	B-Application
,	O
and	O
the	O
latter	O
is	O
defined	O
in	O
IETF	O
.	O
</s>
<s>
Both	O
zip	B-Application
and	O
gzip	B-Application
primarily	O
use	O
the	O
DEFLATE	B-Algorithm
algorithm	O
for	O
compression	B-General_Concept
.	O
</s>
<s>
Likewise	O
,	O
the	O
ZLIB	B-Language
format	O
(	O
IETF	O
)	O
also	O
uses	O
the	O
DEFLATE	B-Algorithm
compression	I-Algorithm
algorithm	I-Algorithm
,	O
but	O
specifies	O
different	O
headers	O
for	O
error	O
and	O
consistency	O
checking	O
.	O
</s>
<s>
Other	O
common	O
,	O
similarly	O
named	O
formats	O
and	O
programs	O
with	O
different	O
native	O
formats	O
include	O
7-Zip	B-Language
,	O
bzip2	B-Application
,	O
and	O
rzip	B-Application
.	O
</s>
<s>
The	O
theoretical	O
maximum	O
compression	B-General_Concept
factor	O
for	O
a	O
raw	O
DEFLATE	B-Algorithm
stream	O
is	O
about	O
1032	O
to	O
one	O
,	O
but	O
by	O
exploiting	O
the	O
ZIP	B-Application
format	O
in	O
unintended	O
ways	O
,	O
ZIP	B-General_Concept
archives	I-General_Concept
with	O
compression	B-General_Concept
ratios	O
of	O
billions	O
to	O
one	O
can	O
be	O
constructed	O
.	O
</s>
<s>
These	O
zip	B-Application
bombs	O
unzip	B-General_Concept
to	O
extremely	O
large	O
sizes	O
,	O
overwhelming	O
the	O
capacity	O
of	O
the	O
computer	O
they	O
are	O
decompressed	O
on	O
.	O
</s>
