<s>
The	O
certification	B-Protocol
path	I-Protocol
validation	I-Protocol
algorithm	I-Protocol
is	O
the	O
algorithm	O
which	O
verifies	O
that	O
a	O
given	O
certificate	O
path	O
is	O
valid	O
under	O
a	O
given	O
public	B-Architecture
key	I-Architecture
infrastructure	I-Architecture
(	O
PKI	O
)	O
.	O
</s>
<s>
A	O
path	O
starts	O
with	O
the	O
Subject	O
certificate	O
and	O
proceeds	O
through	O
a	O
number	O
of	O
intermediate	O
certificates	O
up	O
to	O
a	O
trusted	O
root	B-Protocol
certificate	I-Protocol
,	O
typically	O
issued	O
by	O
a	O
trusted	O
certificate	B-Architecture
authority	I-Architecture
(	O
CA	O
)	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
a	O
hierarchical	O
PKI	O
,	O
a	O
certificate	O
chain	O
starting	O
with	O
a	O
web	O
server	O
certificate	O
might	O
lead	O
to	O
a	O
small	O
CA	O
,	O
then	O
to	O
an	O
intermediate	O
CA	O
,	O
then	O
to	O
a	O
large	O
CA	O
whose	O
trust	B-General_Concept
anchor	I-General_Concept
is	O
present	O
in	O
the	O
relying	O
party	O
's	O
web	O
browser	O
.	O
</s>
<s>
In	O
a	O
bridged	O
PKI	O
,	O
a	O
certificate	O
chain	O
starting	O
with	O
a	O
user	O
at	O
Company	O
A	O
might	O
lead	O
to	O
Company	O
A	O
's	O
CA	B-Architecture
certificate	I-Architecture
,	O
then	O
to	O
a	O
bridge	O
CA	O
,	O
then	O
to	O
company	O
B	O
's	O
CA	B-Architecture
certificate	I-Architecture
,	O
then	O
to	O
company	O
B	O
's	O
trust	B-General_Concept
anchor	I-General_Concept
,	O
which	O
a	O
relying	O
party	O
at	O
company	O
B	O
could	O
trust	O
.	O
</s>
<s>
The	O
list	O
of	O
certificate	B-Protocol
policy	I-Protocol
object	O
identifiers	O
(	O
OIDs	O
)	O
acceptable	O
to	O
the	O
relying	O
party	O
(	O
or	O
any	O
)	O
;	O
</s>
<s>
In	O
the	O
standardized	O
algorithm	O
,	O
the	O
following	O
steps	O
are	O
performed	O
for	O
each	O
certificate	O
in	O
the	O
path	O
,	O
starting	O
from	O
the	O
trust	B-General_Concept
anchor	I-General_Concept
.	O
</s>
<s>
The	O
revocation	O
status	O
is	O
checked	O
,	O
whether	O
by	O
CRL	B-Protocol
,	O
OCSP	B-Protocol
,	O
or	O
some	O
other	O
mechanism	O
,	O
to	O
ensure	O
the	O
certificate	O
is	O
not	O
revoked	O
;	O
</s>
<s>
Name	O
constraints	O
are	O
checked	O
,	O
to	O
make	O
sure	O
the	O
subject	O
name	O
is	O
within	O
the	O
permitted	O
subtrees	O
list	O
of	O
all	O
previous	O
CA	B-Architecture
certificates	I-Architecture
and	O
not	O
within	O
the	O
excluded	O
subtrees	O
list	O
of	O
any	O
previous	O
CA	B-Architecture
certificate	I-Architecture
;	O
</s>
<s>
The	O
asserted	O
certificate	B-Protocol
policy	I-Protocol
OIDs	O
are	O
checked	O
against	O
the	O
permissible	O
OIDs	O
as	O
of	O
the	O
previous	O
certificate	O
,	O
including	O
any	O
policy	O
mapping	O
equivalencies	O
asserted	O
by	O
the	O
previous	O
certificate	O
;	O
</s>
<s>
Policy	O
constraints	O
and	O
basic	O
constraints	O
are	O
checked	O
,	O
to	O
ensure	O
that	O
any	O
explicit	O
policy	O
requirements	O
are	O
not	O
violated	O
and	O
that	O
the	O
certificate	O
is	O
a	O
CA	B-Architecture
certificate	I-Architecture
,	O
respectively	O
.	O
</s>
