<s>
Group	B-Protocol
Domain	I-Protocol
of	I-Protocol
Interpretation	I-Protocol
or	O
GDOI	B-Protocol
is	O
a	O
cryptographic	B-Protocol
protocol	I-Protocol
for	O
group	O
key	O
management	O
.	O
</s>
<s>
The	O
GDOI	B-Protocol
protocol	O
is	O
specified	O
in	O
an	O
IETF	O
Standard	O
,	O
RFC	O
6407	O
,	O
and	O
is	O
based	O
on	O
Internet	B-Protocol
Security	I-Protocol
Association	I-Protocol
and	I-Protocol
Key	I-Protocol
Management	I-Protocol
Protocol	I-Protocol
(	O
ISAKMP	B-Protocol
)	O
,	O
RFC	O
2408	O
,	O
and	O
Internet	B-Protocol
Key	I-Protocol
Exchange	I-Protocol
version	O
1	O
(	O
IKE	O
)	O
.	O
</s>
<s>
Whereas	O
IKE	O
is	O
run	O
between	O
two	O
peers	O
to	O
establish	O
a	O
"	O
pair-wise	O
security	O
association	O
"	O
,	O
GDOI	B-Protocol
protocol	O
is	O
run	O
between	O
a	O
group	O
member	O
and	O
a	O
"	O
group	O
controller/key	O
server	O
"	O
(	O
controller	O
)	O
and	O
establishes	O
a	O
security	O
association	O
among	O
two	O
or	O
more	O
group	O
members	O
.	O
</s>
<s>
GDOI	B-Protocol
"	O
interprets	O
"	O
IKE	O
or	O
ISAKMP	B-Protocol
for	O
the	O
group	O
security	O
domain	O
in	O
addition	O
to	O
pair-wise	O
security	O
associations	O
.	O
</s>
<s>
GDOI	B-Protocol
uses	O
an	O
IKE	O
v1	O
Phase	O
1	O
security	O
association	O
for	O
authenticating	O
a	O
GDOI	B-Protocol
member	O
to	O
a	O
GDOI	B-Protocol
controller	O
.	O
</s>
<s>
The	O
IKE/GDOI	O
Phase	O
1	O
cryptographic	B-Protocol
protocol	I-Protocol
exchange	O
protects	O
a	O
new	O
type	O
of	O
Phase	O
2	O
exchange	O
in	O
which	O
the	O
member	O
requests	O
(	O
"	O
pulls	O
"	O
)	O
group	O
state	O
from	O
the	O
controller	O
.	O
</s>
<s>
The	O
"	O
group	O
key	O
"	O
is	O
the	O
most	O
important	O
state	O
in	O
a	O
GDOI	B-Protocol
member	O
.	O
</s>
<s>
Thus	O
,	O
the	O
group	O
key	O
is	O
also	O
called	O
a	O
"	O
key	O
encrypting	O
key	O
"	O
in	O
GDOI	B-Protocol
.	O
</s>
<s>
Once	O
the	O
"	O
Rekey-SA	O
"	O
is	O
established	O
,	O
the	O
GDOI	B-Protocol
controller	O
can	O
send	O
(	O
"	O
push	O
"	O
)	O
unsolicited	O
updates	O
to	O
the	O
group	O
security	O
association	O
to	O
members	O
over	O
multicast	O
,	O
broadcast	O
or	O
unicast	O
channels	O
.	O
</s>
<s>
This	O
is	O
why	O
GDOI	B-Protocol
is	O
called	O
a	O
"	O
multicast	O
key	O
management	O
system	O
"	O
as	O
it	O
uses	O
and	O
supports	O
multicast	O
messaging	O
for	O
very	O
large	O
groups	O
.	O
</s>
<s>
These	O
multicast	O
messages	O
are	O
unsolicited	O
messages	O
and	O
are	O
therefore	O
called	O
"	O
push	O
"	O
messages	O
,	O
which	O
are	O
unsolicited	O
messages	O
sent	O
from	O
the	O
controller	O
to	O
the	O
members	O
;	O
explicit	O
requests	O
from	O
a	O
member	O
to	O
a	O
controller	O
are	O
called	O
"	O
pull	O
"	O
messages	O
in	O
GDOI	B-Protocol
.	O
</s>
<s>
Thus	O
GDOI	B-Protocol
group	O
key	O
updates	O
are	O
pushed	O
and	O
can	O
reach	O
any	O
number	O
of	O
group	O
members	O
with	O
a	O
single	O
efficient	O
transmission	O
from	O
the	O
controller	O
.	O
</s>
<s>
GDOI	B-Protocol
group	O
key	O
updates	O
also	O
serve	O
to	O
remove	O
members	O
from	O
groups	O
.	O
</s>
<s>
Thus	O
,	O
RFC	O
2627	O
supports	O
efficient	O
group	O
"	O
membership	O
management	O
"	O
for	O
GDOI	B-Protocol
.	O
</s>
<s>
In	O
a	O
practical	O
implementation	O
,	O
GDOI	B-Protocol
group	O
membership	O
management	O
is	O
a	O
separate	O
function	O
that	O
the	O
controller	O
or	O
a	O
AAA	O
function	O
invokes	O
to	O
remove	O
a	O
de-authorized	O
group	O
member	O
.	O
</s>
<s>
The	O
provider	O
or	O
AAA	O
function	O
must	O
have	O
a	O
credential	O
infrastructure	O
such	O
as	O
a	O
Public	B-Architecture
Key	I-Architecture
Infrastructure	I-Architecture
using	O
X.509	O
digital	O
certificates	O
,	O
SPKI	O
or	O
some	O
other	O
credential	O
.	O
</s>
<s>
In	O
an	O
X.509	O
environment	O
,	O
the	O
provider	O
or	O
AAA	O
function	O
will	O
install	O
a	O
certificate	O
to	O
allow	O
a	O
member	O
to	O
join	O
a	O
group	O
when	O
the	O
Group	O
Controller	O
queries	O
the	O
PKI	O
during	O
a	O
GDOI	B-Protocol
Registration	O
exchange	O
when	O
a	O
member	O
attempts	O
to	O
join	O
a	O
group	O
and	O
"	O
pull	O
down	O
"	O
the	O
group	O
state	O
.	O
</s>
<s>
Not	O
all	O
GDOI	B-Protocol
groups	O
make	O
a	O
distinction	O
between	O
sender	O
and	O
receiver	O
,	O
however	O
,	O
and	O
whether	O
or	O
not	O
group	O
members	O
may	O
send	O
to	O
each	O
other	O
is	O
a	O
matter	O
of	O
group	O
policy	O
.	O
</s>
