<s>
In	O
cryptography	O
,	O
a	O
certificate	B-Protocol
revocation	I-Protocol
list	I-Protocol
(	O
or	O
CRL	O
)	O
is	O
"	O
a	O
list	O
of	O
digital	O
certificates	O
that	O
have	O
been	O
revoked	O
by	O
the	O
issuing	O
certificate	B-Architecture
authority	I-Architecture
(	O
CA	O
)	O
before	O
their	O
scheduled	O
expiration	O
date	O
and	O
should	O
no	O
longer	O
be	O
trusted	O
"	O
.	O
</s>
<s>
CRLs	O
are	O
no	O
longer	O
required	O
by	O
the	O
CA/Browser	O
forum	O
,	O
as	O
alternate	O
certificate	B-Protocol
revocation	I-Protocol
technologies	O
(	O
such	O
as	O
OCSP	B-Protocol
)	O
are	O
increasingly	O
used	O
instead	O
.	O
</s>
<s>
Revoked	O
A	O
certificate	O
is	O
irreversibly	O
revoked	O
if	O
,	O
for	O
example	O
,	O
it	O
is	O
discovered	O
that	O
the	O
certificate	B-Architecture
authority	I-Architecture
(	O
CA	O
)	O
had	O
improperly	O
issued	O
a	O
certificate	O
,	O
or	O
if	O
a	O
private-key	B-Algorithm
is	O
thought	O
to	O
have	O
been	O
compromised	O
.	O
</s>
<s>
In	O
a	O
noteworthy	O
example	O
,	O
a	O
certificate	O
for	O
Microsoft	O
was	O
mistakenly	O
issued	O
to	O
an	O
unknown	O
individual	O
,	O
who	O
had	O
successfully	O
posed	O
as	O
Microsoft	O
to	O
the	O
CA	O
contracted	O
to	O
maintain	O
the	O
ActiveX	B-Application
'	O
publisher	O
certificate	O
 '	O
system	O
(	O
VeriSign	B-Application
)	O
.	O
</s>
<s>
This	O
requirement	O
of	O
on-line	O
validation	O
negates	O
one	O
of	O
the	O
original	O
major	O
advantages	O
of	O
PKI	O
over	O
symmetric	B-Algorithm
cryptography	I-Algorithm
protocols	O
,	O
namely	O
that	O
the	O
certificate	O
is	O
"	O
self-authenticating	O
"	O
.	O
</s>
<s>
Symmetric	O
systems	O
such	O
as	O
Kerberos	B-Protocol
also	O
depend	O
on	O
the	O
existence	O
of	O
on-line	O
services	O
(	O
a	O
key	O
distribution	O
center	O
in	O
the	O
case	O
of	O
Kerberos	B-Protocol
)	O
.	O
</s>
<s>
As	O
the	O
certificate	B-Architecture
authority	I-Architecture
is	O
tasked	O
with	O
enforcing	O
the	O
operational	O
policy	O
for	O
issuing	O
certificates	O
,	O
they	O
typically	O
are	O
responsible	O
for	O
determining	O
if	O
and	O
when	O
revocation	O
is	O
appropriate	O
by	O
interpreting	O
the	O
operational	O
policy	O
.	O
</s>
<s>
This	O
issue	O
exists	O
for	O
Kerberos	B-Protocol
systems	O
as	O
well	O
,	O
where	O
failure	O
to	O
retrieve	O
a	O
current	O
authentication	O
token	O
will	O
prevent	O
system	O
access	O
.	O
</s>
<s>
An	O
alternative	O
to	O
using	O
CRLs	O
is	O
the	O
certificate	O
validation	O
protocol	O
known	O
as	O
Online	B-Protocol
Certificate	I-Protocol
Status	I-Protocol
Protocol	I-Protocol
(	O
OCSP	B-Protocol
)	O
.	O
</s>
<s>
OCSP	B-Protocol
has	O
the	O
primary	O
benefit	O
of	O
requiring	O
less	O
network	O
bandwidth	O
,	O
enabling	O
real-time	O
and	O
near	O
real-time	O
status	O
checks	O
for	O
high	O
volume	O
or	O
high-value	O
operations	O
.	O
</s>
<s>
As	O
of	O
Firefox	O
28	O
,	O
Mozilla	O
has	O
announced	O
they	O
are	O
deprecating	O
CRL	O
in	O
favour	O
of	O
OCSP	B-Protocol
.	O
</s>
<s>
An	O
authority	O
revocation	B-Protocol
list	I-Protocol
(	O
ARL	O
)	O
is	O
a	O
form	O
of	O
CRL	O
containing	O
revoked	O
certificates	O
issued	O
to	O
certificate	B-Architecture
authorities	I-Architecture
,	O
contrary	O
to	O
CRLs	O
which	O
contain	O
revoked	O
end-entity	O
certificates	O
.	O
</s>
