<s>
In	O
computing	O
,	O
Internet	B-Protocol
Key	I-Protocol
Exchange	I-Protocol
(	O
IKE	O
,	O
sometimes	O
IKEv1	B-Protocol
or	O
IKEv2	B-Protocol
,	O
depending	O
on	O
version	O
)	O
is	O
the	O
protocol	O
used	O
to	O
set	O
up	O
a	O
security	B-Protocol
association	I-Protocol
(	O
SA	O
)	O
in	O
the	O
IPsec	B-Protocol
protocol	O
suite	O
.	O
</s>
<s>
IKE	O
builds	O
upon	O
the	O
Oakley	B-Protocol
protocol	I-Protocol
and	O
ISAKMP	B-Protocol
.	O
</s>
<s>
IKE	O
uses	O
X.509	O
certificates	O
for	O
authentication	O
‒	O
either	O
pre-shared	O
or	O
distributed	O
using	O
DNS	B-Protocol
(	O
preferably	O
with	O
DNSSEC	B-Protocol
)	O
‒	O
and	O
a	O
Diffie	B-Protocol
–	I-Protocol
Hellman	I-Protocol
key	I-Protocol
exchange	I-Protocol
to	O
set	O
up	O
a	O
shared	O
session	O
secret	O
from	O
which	O
cryptographic	O
keys	O
are	O
derived	O
.	O
</s>
<s>
defined	O
the	O
Internet	O
IP	B-Protocol
Security	I-Protocol
Domain	O
of	O
Interpretation	O
for	O
ISAKMP	B-Protocol
.	O
</s>
<s>
defined	O
the	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
</s>
<s>
defined	O
the	O
Internet	B-Protocol
Key	I-Protocol
Exchange	I-Protocol
(	O
IKE	O
)	O
.	O
</s>
<s>
updated	O
IKE	O
to	O
version	O
two	O
(	O
IKEv2	B-Protocol
)	O
in	O
December	O
2005	O
.	O
clarified	O
some	O
open	O
details	O
in	O
October	O
2006	O
.	O
combined	O
these	O
two	O
documents	O
plus	O
additional	O
clarifications	O
into	O
the	O
updated	O
IKEv2	B-Protocol
,	O
published	O
in	O
September	O
2010	O
.	O
</s>
<s>
Most	O
IPsec	B-Protocol
implementations	I-Protocol
consist	O
of	O
an	O
IKE	O
daemon	B-Operating_System
that	O
runs	O
in	O
user	B-Operating_System
space	I-Operating_System
and	O
an	O
IPsec	B-Protocol
stack	O
in	O
the	O
kernel	B-Operating_System
that	O
processes	O
the	O
actual	O
IP	B-Protocol
packets	O
.	O
</s>
<s>
User-space	B-Operating_System
daemons	B-Operating_System
have	O
easy	O
access	O
to	O
mass	O
storage	O
containing	O
configuration	O
information	O
,	O
such	O
as	O
the	O
IPsec	B-Protocol
endpoint	O
addresses	O
,	O
keys	O
and	O
certificates	O
,	O
as	O
required	O
.	O
</s>
<s>
Kernel	B-Operating_System
modules	O
,	O
on	O
the	O
other	O
hand	O
,	O
can	O
process	O
packets	O
efficiently	O
and	O
with	O
minimum	O
overhead	O
—	O
which	O
is	O
important	O
for	O
performance	O
reasons	O
.	O
</s>
<s>
The	O
IKE	O
protocol	O
uses	O
UDP	B-Protocol
packets	I-Protocol
,	O
usually	O
on	O
port	O
500	O
,	O
and	O
generally	O
requires	O
4	O
–	O
6	O
packets	O
with	O
2	O
–	O
3	O
round	O
trips	O
to	O
create	O
an	O
ISAKMP	B-Protocol
security	B-Protocol
association	I-Protocol
(	O
SA	O
)	O
on	O
both	O
sides	O
.	O
</s>
<s>
The	O
negotiated	O
key	O
material	O
is	O
then	O
given	O
to	O
the	O
IPsec	B-Protocol
stack	O
.	O
</s>
<s>
For	O
instance	O
,	O
this	O
could	O
be	O
an	O
AES	B-Algorithm
key	I-Algorithm
,	O
information	O
identifying	O
the	O
IP	B-Protocol
endpoints	O
and	O
ports	O
that	O
are	O
to	O
be	O
protected	O
,	O
as	O
well	O
as	O
what	O
type	O
of	O
IPsec	B-Protocol
tunnel	O
has	O
been	O
created	O
.	O
</s>
<s>
The	O
IPsec	B-Protocol
stack	O
,	O
in	O
turn	O
,	O
intercepts	O
the	O
relevant	O
IP	B-Protocol
packets	O
if	O
and	O
where	O
appropriate	O
and	O
performs	O
encryption/decryption	O
as	O
required	O
.	O
</s>
<s>
Implementations	O
vary	O
on	O
how	O
the	O
interception	O
of	O
the	O
packets	O
is	O
done	O
—	O
for	O
example	O
,	O
some	O
use	O
virtual	O
devices	O
,	O
others	O
take	O
a	O
slice	O
out	O
of	O
the	O
firewall	B-Application
,	O
etc	O
.	O
</s>
<s>
IKEv1	B-Protocol
consists	O
of	O
two	O
phases	O
:	O
phase	O
1	O
and	O
phase	O
2	O
.	O
</s>
<s>
IKE	O
phase	O
one	O
's	O
purpose	O
is	O
to	O
establish	O
a	O
secure	O
authenticated	O
communication	O
channel	O
by	O
using	O
the	O
Diffie	B-Protocol
–	I-Protocol
Hellman	I-Protocol
key	I-Protocol
exchange	I-Protocol
algorithm	O
to	O
generate	O
a	O
shared	O
secret	O
key	O
to	O
encrypt	O
further	O
IKE	O
communications	O
.	O
</s>
<s>
This	O
negotiation	O
results	O
in	O
one	O
single	O
bi-directional	O
ISAKMP	B-Protocol
security	B-Protocol
association	I-Protocol
.	O
</s>
<s>
During	O
IKE	O
phase	O
two	O
,	O
the	O
IKE	O
peers	O
use	O
the	O
secure	O
channel	O
established	O
in	O
Phase	O
1	O
to	O
negotiate	O
Security	B-Protocol
Associations	I-Protocol
on	O
behalf	O
of	O
other	O
services	O
like	O
IPsec	B-Protocol
.	O
</s>
<s>
The	O
negotiation	O
results	O
in	O
a	O
minimum	O
of	O
two	O
unidirectional	O
security	B-Protocol
associations	I-Protocol
(	O
one	O
inbound	O
and	O
one	O
outbound	O
)	O
.	O
</s>
<s>
Consequently	O
,	O
both	O
sides	O
of	O
an	O
IKE	O
had	O
to	O
exactly	O
agree	O
on	O
the	O
type	O
of	O
security	B-Protocol
association	I-Protocol
they	O
wanted	O
to	O
create	O
–	O
option	O
by	O
option	O
–	O
or	O
a	O
connection	O
could	O
not	O
be	O
established	O
.	O
</s>
<s>
The	O
IKE	O
specifications	O
were	O
open	O
to	O
a	O
significant	O
degree	O
of	O
interpretation	O
,	O
bordering	O
on	O
design	O
faults	O
(	O
Dead-Peer-Detection	B-Protocol
being	O
a	O
case	O
in	O
point	O
)	O
,	O
giving	O
rise	O
to	O
different	O
IKE	O
implementations	O
not	O
being	O
able	O
to	O
create	O
an	O
agreed-upon	O
security	B-Protocol
association	I-Protocol
at	O
all	O
for	O
many	O
combinations	O
of	O
options	O
,	O
however	O
correctly	O
configured	O
they	O
might	O
appear	O
at	O
either	O
end	O
.	O
</s>
<s>
The	O
IKEv2	B-Protocol
protocol	O
was	O
described	O
in	O
Appendix	O
A	O
of	O
RFC	O
4306	O
in	O
2005	O
.	O
</s>
<s>
Fewer	O
Request	O
for	O
Comments	O
(	O
RFCs	O
)	O
:	O
The	O
specifications	O
for	O
IKE	O
were	O
covered	O
in	O
at	O
least	O
three	O
RFCs	O
,	O
more	O
if	O
one	O
takes	O
into	O
account	O
NAT	B-Protocol
traversal	I-Protocol
and	O
other	O
extensions	O
that	O
are	O
in	O
common	O
use	O
.	O
</s>
<s>
IKEv2	B-Protocol
combines	O
these	O
in	O
one	O
RFC	O
as	O
well	O
as	O
making	O
improvements	O
to	O
support	O
for	O
NAT	B-Protocol
traversal	I-Protocol
(	O
Network	B-Protocol
Address	I-Protocol
Translation	I-Protocol
(	O
NAT	B-Protocol
)	O
)	O
and	O
firewall	B-Application
traversal	O
in	O
general	O
.	O
</s>
<s>
Standard	O
Mobility	O
support	O
:	O
There	O
is	O
a	O
standard	O
extension	O
for	O
IKEv2	B-Protocol
named	O
[	O
rfc:4555	O
Mobility	O
and	O
Multihoming	O
Protocol ]	O
(	O
MOBIKE	O
)	O
(	O
see	O
also	O
,	O
IPsec	B-Protocol
)	O
used	O
to	O
support	O
mobility	O
and	O
multihoming	O
for	O
it	O
and	O
Encapsulating	O
Security	O
Payload	O
(	O
ESP	O
)	O
.	O
</s>
<s>
By	O
use	O
of	O
this	O
extension	O
IKEv2	B-Protocol
and	O
IPsec	B-Protocol
can	O
be	O
used	O
by	O
mobile	O
and	O
multihomed	O
users	O
.	O
</s>
<s>
NAT	B-Protocol
traversal	I-Protocol
:	O
The	O
encapsulation	O
of	O
IKE	O
and	O
ESP	O
in	O
User	B-Protocol
Datagram	I-Protocol
Protocol	I-Protocol
(	O
UDP	B-Protocol
port	O
4500	O
)	O
enables	O
these	O
protocols	O
to	O
pass	O
through	O
a	O
device	O
or	O
firewall	B-Application
performing	O
NAT	B-Protocol
.	O
</s>
<s>
Stream	B-Protocol
Control	I-Protocol
Transmission	I-Protocol
Protocol	I-Protocol
(	O
SCTP	B-Protocol
)	O
support	O
:	O
IKEv2	B-Protocol
allows	O
for	O
the	O
SCTP	B-Protocol
protocol	O
as	O
used	O
in	O
Internet	B-Application
telephony	I-Application
protocol	O
,	O
Voice	B-Application
over	I-Application
IP	I-Application
(	O
VoIP	B-Application
)	O
.	O
</s>
<s>
Simple	O
message	O
exchange	O
:	O
IKEv2	B-Protocol
has	O
one	O
four-message	O
initial	O
exchange	O
mechanism	O
where	O
IKE	O
provided	O
eight	O
distinctly	O
different	O
initial	O
exchange	O
mechanisms	O
,	O
each	O
one	O
of	O
which	O
had	O
slight	O
advantages	O
and	O
disadvantages	O
.	O
</s>
<s>
Fewer	O
cryptographic	O
mechanisms	O
:	O
IKEv2	B-Protocol
uses	O
cryptographic	O
mechanisms	O
to	O
protect	O
its	O
packets	O
that	O
are	O
very	O
similar	O
to	O
what	O
IPsec	B-Protocol
ESP	O
uses	O
to	O
protect	O
the	O
IPsec	B-Protocol
packets	O
.	O
</s>
<s>
Reliability	O
and	O
State	O
management	O
:	O
IKEv2	B-Protocol
uses	O
sequence	O
numbers	O
and	O
acknowledgments	O
to	O
provide	O
reliability	O
and	O
mandates	O
some	O
error	O
processing	O
logistics	O
and	O
shared	O
state	O
management	O
.	O
</s>
<s>
Work	O
arounds	O
(	O
such	O
as	O
Dead-Peer-Detection	B-Protocol
)	O
were	O
developed	O
but	O
not	O
standardized	O
.	O
</s>
<s>
Denial	O
of	O
Service	O
(	O
DoS	O
)	O
attack	O
resilience	O
:	O
IKEv2	B-Protocol
does	O
not	O
perform	O
much	O
processing	O
until	O
it	O
determines	O
if	O
the	O
requester	O
actually	O
exists	O
.	O
</s>
<s>
Supposing	O
HostA	O
has	O
a	O
Security	B-Protocol
Parameter	I-Protocol
Index	I-Protocol
(	O
SPI	B-Protocol
)	O
of	O
A	O
and	O
HostB	O
has	O
an	O
SPI	B-Protocol
of	O
B	O
,	O
the	O
scenario	O
would	O
look	O
like	O
this	O
:	O
</s>
<s>
of	O
modernizing	O
the	O
IKEv2	B-Protocol
protocol	O
and	O
adapting	O
it	O
better	O
to	O
high	O
volume	O
,	O
</s>
<s>
IKE	O
session	O
resumption	O
:	O
the	O
ability	O
to	O
resume	O
a	O
failed	O
IKE/IPsec	O
"	O
session	O
"	O
after	O
a	O
failure	O
,	O
without	O
the	O
need	O
to	O
go	O
through	O
the	O
entire	O
IKE	O
setup	O
process	O
(	O
)	O
.	O
</s>
<s>
IPsec	B-Protocol
traffic	O
visibility	O
:	O
special	O
tagging	O
of	O
ESP	O
packets	O
that	O
are	O
authenticated	O
but	O
not	O
encrypted	O
,	O
with	O
the	O
goal	O
of	O
making	O
it	O
easier	O
for	O
middleboxes	O
(	O
such	O
as	O
intrusion	O
detection	O
systems	O
)	O
to	O
analyze	O
the	O
flow	O
(	O
)	O
.	O
</s>
<s>
Mutual	O
EAP	B-Protocol
authentication	O
:	O
support	O
for	O
EAP-only	O
(	O
i.e.	O
,	O
certificate-less	O
)	O
authentication	O
of	O
both	O
of	O
the	O
IKE	O
peers	O
;	O
the	O
goal	O
is	O
to	O
allow	O
for	O
modern	O
password-based	B-Protocol
authentication	I-Protocol
methods	O
to	O
be	O
used	O
(	O
)	O
.	O
</s>
<s>
High	O
availability	O
extensions	O
:	O
improving	O
IKE/IPsec	O
-level	O
protocol	O
synchronization	O
between	O
a	O
cluster	O
of	O
IPsec	B-Protocol
endpoints	O
and	O
a	O
peer	O
,	O
to	O
reduce	O
the	O
probability	O
of	O
dropped	O
connections	O
after	O
a	O
failover	O
event	O
(	O
)	O
.	O
</s>
<s>
IKE	O
is	O
supported	O
as	O
part	O
of	O
the	O
IPsec	B-Protocol
implementation	O
in	O
Windows	B-Application
2000	I-Application
,	O
Windows	B-Application
XP	I-Application
,	O
Windows	B-Application
Server	I-Application
2003	I-Application
,	O
Windows	B-Application
Vista	I-Application
and	O
Windows	B-Device
Server	I-Device
2008	I-Device
.	O
</s>
<s>
The	O
ISAKMP/IKE	O
implementation	O
was	O
jointly	O
developed	O
by	O
Cisco	O
and	O
Microsoft	O
.	O
</s>
<s>
Microsoft	B-Device
Windows	I-Device
7	I-Device
and	O
Windows	B-Device
Server	I-Device
2008	I-Device
R2	I-Device
partially	O
support	O
IKEv2	B-Protocol
(	O
)	O
as	O
well	O
as	O
MOBIKE	O
(	O
)	O
through	O
the	O
VPN	O
Reconnect	O
feature	O
(	O
also	O
known	O
as	O
Agile	O
VPN	O
)	O
.	O
</s>
<s>
There	O
are	O
several	O
open	O
source	O
implementations	O
of	O
IPsec	B-Protocol
with	O
associated	O
IKE	O
capabilities	O
.	O
</s>
<s>
On	O
Linux	B-Operating_System
,	O
Libreswan	B-Application
,	O
Openswan	B-Protocol
and	O
strongSwan	B-Protocol
implementations	O
provide	O
an	O
IKE	O
daemon	B-Operating_System
which	O
can	O
configure	O
(	O
i.e.	O
,	O
establish	O
SAs	O
)	O
to	O
the	O
KLIPS	O
or	O
XFRM/NETKEY	O
kernel-based	O
IPsec	B-Protocol
stacks	O
.	O
</s>
<s>
XFRM/NETKEY	O
is	O
the	O
Linux	B-Operating_System
native	O
IPsec	B-Protocol
implementation	O
available	O
as	O
of	O
version	O
2.6	O
.	O
</s>
<s>
The	O
Berkeley	B-Operating_System
Software	I-Operating_System
Distributions	I-Operating_System
also	O
have	O
an	O
IPsec	B-Protocol
implementation	O
and	O
IKE	O
daemon	B-Operating_System
,	O
and	O
most	O
importantly	O
a	O
cryptographic	O
framework	O
(	O
OpenBSD	B-Operating_System
Cryptographic	O
Framework	O
,	O
OCF	O
)	O
,	O
which	O
makes	O
supporting	O
cryptographic	B-General_Concept
accelerators	I-General_Concept
much	O
easier	O
.	O
</s>
<s>
OCF	O
has	O
recently	O
been	O
ported	O
to	O
Linux	B-Operating_System
.	O
</s>
<s>
A	O
significant	O
number	O
of	O
network	O
equipment	O
vendors	O
have	O
created	O
their	O
own	O
IKE	O
daemons	B-Operating_System
(	O
and	O
IPsec	B-Protocol
implementations	I-Protocol
)	O
,	O
or	O
license	O
a	O
stack	O
from	O
one	O
another	O
.	O
</s>
<s>
There	O
are	O
a	O
number	O
of	O
implementations	O
of	O
IKEv2	B-Protocol
and	O
some	O
of	O
the	O
companies	O
dealing	O
in	O
IPsec	B-Protocol
certification	O
and	O
interoperability	O
testing	O
are	O
starting	O
to	O
hold	O
workshops	O
for	O
testing	O
as	O
well	O
as	O
updated	O
certification	O
requirements	O
to	O
deal	O
with	O
IKEv2	B-Protocol
testing	O
.	O
</s>
<s>
The	O
following	O
open	O
source	O
implementations	O
of	O
IKEv2	B-Protocol
are	O
currently	O
available	O
:	O
</s>
<s>
strongSwan	B-Protocol
,	O
</s>
<s>
Libreswan	B-Application
,	O
</s>
<s>
Openswan	B-Protocol
,	O
</s>
<s>
Racoon	O
from	O
the	O
KAME	B-Application
project	I-Application
,	O
</s>
<s>
Leaked	O
NSA	O
presentations	O
released	O
by	O
Der	O
Spiegel	O
indicate	O
that	O
IKE	O
is	O
being	O
exploited	O
in	O
an	O
unknown	O
manner	O
to	O
decrypt	O
IPsec	B-Protocol
traffic	O
,	O
as	O
is	O
ISAKMP	B-Protocol
.	O
</s>
<s>
The	O
researchers	O
who	O
discovered	O
the	O
Logjam	B-Protocol
attack	I-Protocol
state	O
that	O
breaking	O
a	O
1024-bit	O
Diffie	B-Protocol
–	I-Protocol
Hellman	I-Protocol
group	I-Protocol
would	O
break	O
66%	O
of	O
VPN	O
servers	O
,	O
18%	O
of	O
the	O
top	O
million	O
HTTPS	O
domains	O
,	O
and	O
26%	O
of	O
SSH	O
servers	O
,	O
which	O
the	O
researchers	O
claim	O
is	O
consistent	O
with	O
the	O
leaks	O
.	O
</s>
<s>
IPsec	B-Protocol
VPN	O
configurations	O
which	O
allow	O
for	O
negotiation	O
of	O
multiple	O
configurations	O
are	O
subject	O
to	O
MITM-based	O
downgrade	O
attacks	O
between	O
the	O
offered	O
configurations	O
,	O
with	O
both	O
IKEv1	B-Protocol
and	O
IKEv2	B-Protocol
.	O
</s>
<s>
For	O
the	O
IKEv1	B-Protocol
this	O
is	O
true	O
for	O
main	O
mode	O
and	O
aggressive	O
mode	O
.	O
</s>
