<s>
IPSW	B-Operating_System
,	O
iPhone	O
Software	O
,	O
is	O
a	O
file	O
format	O
used	O
to	O
install	O
iOS	B-Application
,	O
iPadOS	B-Operating_System
,	O
tvOS	B-Operating_System
,	O
HomePod	B-Device
,	O
and	O
most	O
recently	O
,	O
macOS	B-Application
firmware	B-Application
for	O
devices	O
equipped	O
with	O
Apple	B-Device
silicon	I-Device
.	O
</s>
<s>
All	O
Apple	O
devices	O
share	O
the	O
same	O
IPSW	B-Operating_System
file	O
format	O
for	O
iOS	B-Application
firmware	B-Application
and	O
their	O
derivatives	O
,	O
allowing	O
users	O
to	O
flash	O
their	O
devices	O
through	O
Finder	B-Application
or	O
iTunes	B-Operating_System
on	O
macOS	B-Application
or	O
Windows	O
,	O
respectively	O
.	O
</s>
<s>
Users	O
can	O
flash	O
Apple	B-Device
silicon	I-Device
Macs	O
through	O
Apple	B-Operating_System
Configurator	I-Operating_System
2	I-Operating_System
.	O
</s>
<s>
The	O
.ipsw	B-Operating_System
file	O
itself	O
is	O
a	O
compressed	B-Application
archive	I-Application
file	O
(	O
renamed	O
Zip	B-General_Concept
archive	I-General_Concept
)	O
containing	O
at	O
least	O
three	O
Apple	B-Operating_System
Disk	I-Operating_System
Image	I-Operating_System
files	O
with	O
one	O
containing	O
the	O
root	B-Application
file	I-Application
system	I-Application
of	O
the	O
OS	O
and	O
two	O
ram	B-Application
disks	I-Application
for	O
restore	O
and	O
update	O
.	O
</s>
<s>
tvOS	B-Operating_System
,	O
audioOS	B-Device
and	O
macOS	B-Application
also	O
include	O
a	O
disk	O
image	O
for	O
the	O
recovery	O
environment	O
(	O
recoveryOS	O
)	O
.	O
</s>
<s>
The	O
file	O
also	O
holds	O
the	O
kernel	O
caches	O
,	O
and	O
a	O
"	O
Firmware	B-Application
"	O
folder	O
which	O
contains	O
iBoot	B-Operating_System
,	O
LLB	O
(	O
Low-Level	O
Bootloader	B-Application
)	O
,	O
iBSS	O
(	O
iBoot	B-Operating_System
Single	O
Stage	O
)	O
,	O
iBEC	O
(	O
iBoot	B-Operating_System
Epoch	O
Change	O
)	O
,	O
the	O
Secure	O
Enclave	O
Processor	O
firmware	B-Application
,	O
the	O
Device	O
Tree	O
,	O
Firmware	B-Application
Images	O
(	O
Apple	O
logo	O
,	O
battery	O
images	O
,	O
Recovery	O
mode	O
screen	O
and	O
more	O
)	O
,	O
baseband	O
firmware	B-Application
files	O
in	O
.bbfw	O
format	O
(	O
renamed	O
zip	B-General_Concept
file	I-General_Concept
)	O
,	O
and	O
other	O
firmware	B-Application
files	O
.	O
</s>
<s>
There	O
are	O
two	O
more	O
files	O
named	O
"	O
BuildManifest.plist	O
"	O
and	O
"	O
Restore.plist	O
"	O
,	O
both	O
property	B-Application
lists	I-Application
that	O
contain	O
compatibility	O
information	O
and	O
SHA-256	B-Algorithm
hashes	I-Algorithm
for	O
different	O
components	O
.	O
</s>
<s>
BuildManifest.plist	O
is	O
sent	O
to	O
Apple	O
's	O
TSS	O
server	O
and	O
checked	O
in	O
order	O
to	O
obtain	O
SHSH	B-Operating_System
blobs	I-Operating_System
before	O
every	O
restore	O
.	O
</s>
<s>
Without	O
SHSH	B-Operating_System
blobs	I-Operating_System
,	O
the	O
device	O
will	O
refuse	O
to	O
restore	O
,	O
thus	O
making	O
downgrades	O
very	O
difficult	O
to	O
achieve	O
.	O
</s>
<s>
The	O
archive	B-Application
is	O
not	O
password-protected	O
,	O
but	O
iBoot	B-Operating_System
,	O
LLB	O
,	O
iBEC	O
,	O
iBSS	O
,	O
iBootData	O
and	O
the	O
Secure	O
Enclave	O
Processor	O
firmware	B-Application
images	O
inside	O
it	O
are	O
encrypted	O
with	O
AES	B-Algorithm
.	O
</s>
<s>
Until	O
iOS	B-Operating_System
10	I-Operating_System
,	O
all	O
the	O
firmware	B-Application
files	O
(	O
including	O
the	O
root	B-Application
file	I-Application
system	I-Application
and	O
Restore	O
and	O
Update	O
ramdisks	B-Application
)	O
were	O
encrypted	O
.	O
</s>
<s>
While	O
Apple	O
does	O
not	O
release	O
these	O
keys	O
,	O
they	O
can	O
be	O
extracted	O
using	O
different	O
iBoot	B-Operating_System
or	O
bootloader	B-Application
exploits	O
,	O
such	O
as	O
limera1n	O
(	O
created	O
by	O
George	O
Hotz	O
,	O
more	O
commonly	O
known	O
as	O
geohot	O
)	O
.	O
</s>
<s>
Since	O
then	O
,	O
many	O
tools	O
were	O
created	O
for	O
the	O
decryption	O
and	O
modification	O
of	O
the	O
root	B-Application
file	I-Application
system	I-Application
.	O
</s>
<s>
After	O
the	O
2015	O
San	O
Bernardino	O
attack	O
,	O
the	O
FBI	O
recovered	O
the	O
shooter	O
's	O
iPhone	B-Operating_System
5C	I-Operating_System
,	O
which	O
belonged	O
to	O
the	O
San	O
Bernardino	O
County	O
Department	O
of	O
Public	O
Health	O
.	O
</s>
<s>
The	O
FBI	O
recovered	O
iCloud	B-Application
backups	O
from	O
one	O
and	O
a	O
half	O
months	O
before	O
the	O
shooting	O
,	O
and	O
wanted	O
to	O
access	O
encrypted	O
files	O
on	O
the	O
device	O
.	O
</s>
<s>
The	O
U.S.	O
government	O
ordered	O
Apple	O
to	O
produce	O
an	O
IPSW	B-Operating_System
file	O
that	O
would	O
allow	O
investigators	O
to	O
brute	O
force	O
the	O
passcode	O
of	O
the	O
iPhone	O
.	O
</s>
<s>
The	O
order	O
used	O
the	O
All	O
Writs	O
Act	O
,	O
originally	O
created	O
by	O
the	O
Judiciary	O
Act	O
of	O
1789	O
,	O
to	O
demand	O
the	O
firmware	B-Application
,	O
in	O
the	O
same	O
way	O
as	O
other	O
smartphone	O
manufacturers	O
have	O
been	O
ordered	O
to	O
comply	O
.	O
</s>
