<s>
An	O
offline	B-Protocol
root	I-Protocol
certificate	I-Protocol
authority	I-Protocol
is	O
a	O
certificate	B-Architecture
authority	I-Architecture
(	O
as	O
defined	O
in	O
the	O
X.509	O
standard	O
and	O
)	O
which	O
has	O
been	O
isolated	O
from	O
network	O
access	O
,	O
and	O
is	O
often	O
kept	O
in	O
a	O
powered-down	O
state	O
.	O
</s>
<s>
In	O
a	O
public	B-Architecture
key	I-Architecture
infrastructure	I-Architecture
,	O
the	O
chain	O
of	O
trusted	O
authorities	O
begins	O
with	O
the	O
root	B-Protocol
certificate	I-Protocol
authority	I-Protocol
(	O
root	B-Protocol
CA	I-Protocol
)	O
.	O
</s>
<s>
Once	O
the	O
root	B-Protocol
CA	I-Protocol
is	O
installed	O
and	O
its	O
root	B-Protocol
certificate	I-Protocol
is	O
created	O
,	O
the	O
next	O
action	O
taken	O
by	O
the	O
administrator	O
of	O
the	O
root	B-Protocol
CA	I-Protocol
is	O
to	O
issue	O
certificates	O
authorizing	O
intermediate	O
(	O
or	O
subordinate	O
)	O
CAs	O
.	O
</s>
<s>
This	O
creates	O
the	O
ability	O
to	O
issue	O
,	O
distribute	O
and	O
revoke	O
digital	O
certificates	O
without	O
the	O
direct	O
action	O
of	O
the	O
root	B-Protocol
CA	I-Protocol
.	O
</s>
<s>
Because	O
the	O
consequences	O
of	O
a	O
compromised	O
root	B-Protocol
CA	I-Protocol
are	O
so	O
great	O
(	O
up	O
to	O
and	O
including	O
the	O
need	O
to	O
re-issue	O
each	O
and	O
every	O
certificate	O
in	O
the	O
PKI	O
)	O
,	O
all	O
root	B-Protocol
CAs	I-Protocol
must	O
be	O
kept	O
safe	O
from	O
unauthorized	O
access	O
.	O
</s>
<s>
A	O
common	O
method	O
to	O
ensure	O
the	O
security	O
and	O
integrity	O
of	O
a	O
root	B-Protocol
CA	I-Protocol
is	O
to	O
keep	O
it	O
in	O
an	O
offline	O
state	O
.	O
</s>
<s>
A	O
drawback	O
to	O
offline	O
operation	O
is	O
that	O
hosting	O
of	O
a	O
certificate	B-Protocol
revocation	I-Protocol
list	I-Protocol
by	O
the	O
root	B-Protocol
CA	I-Protocol
is	O
not	O
possible	O
(	O
as	O
it	O
is	O
unable	O
to	O
respond	O
to	O
CRL	O
requests	O
via	O
protocols	O
such	O
as	O
HTTP	B-Protocol
,	O
LDAP	B-Protocol
or	O
OCSP	B-Protocol
)	O
.	O
</s>
<s>
However	O
,	O
it	O
is	O
possible	O
to	O
move	O
certificate	O
validation	O
functionality	O
into	O
a	O
dedicated	O
validation	B-Protocol
authority	I-Protocol
authorized	O
by	O
the	O
offline	B-Protocol
root	I-Protocol
CA	I-Protocol
.	O
</s>
<s>
To	O
better	O
understand	O
how	O
an	O
offline	B-Protocol
root	I-Protocol
CA	I-Protocol
can	O
greatly	O
improve	O
the	O
security	O
and	O
integrity	O
of	O
a	O
PKI	O
,	O
it	O
is	O
important	O
to	O
realize	O
that	O
a	O
CRL	O
is	O
specific	O
to	O
the	O
CA	O
which	O
issued	O
the	O
certificates	O
on	O
the	O
list	O
.	O
</s>
<s>
Consider	O
the	O
scenario	O
where	O
a	O
root	B-Protocol
CA	I-Protocol
issues	O
certificates	O
to	O
three	O
intermediate	O
CAs	O
:	O
A	O
,	O
B	O
,	O
and	O
C	O
:	O
</s>
<s>
The	O
root	B-Protocol
CA	I-Protocol
has	O
issued	O
a	O
total	O
of	O
three	O
certificates	O
.	O
</s>
<s>
However	O
,	O
because	O
the	O
root	B-Protocol
CA	I-Protocol
has	O
only	O
issued	O
three	O
certificates	O
(	O
to	O
each	O
of	O
the	O
intermediate	O
CAs	O
)	O
,	O
the	O
maximum	O
size	O
of	O
its	O
CRL	O
is	O
:	O
</s>
<s>
Therefore	O
,	O
the	O
overall	O
burden	O
of	O
maintaining	O
and	O
hosting	O
a	O
CRL	O
specific	O
to	O
the	O
root	B-Protocol
CA	I-Protocol
is	O
minimized	O
by	O
the	O
use	O
of	O
intermediate	O
CAs	O
,	O
as	O
well	O
as	O
the	O
burden	O
of	O
maintaining	O
an	O
associated	O
validation	B-Protocol
authority	I-Protocol
.	O
</s>
