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24 Security Examples
Reply to: 24 Security Examples
Ran,
I agree with your comments about considering the SDNS work.
>It seemed to me like we ought to _at least_ seriously consider using the
SDNS work, including
>the SDNS Key Mgmt mechanisms, as a good base to work from. Other
considerations aside,
>a lot of work has been done on that and as near as I can tell, all of the
US DoD will be moving
>in an SDNS-like direction (which means that leveraging that work should
help the availability
>of commercial implementations that would eventually [preferably soon] be
really interoperable.
>
>I haven't studied the SP3 and NLSP documents side by side recently, but am
doing so now.
>If someone had an existing summary of differences that they could post to
this list, it would
>be generally useful, I think.
>
>Ran
>atkinson@itd.nrl.navy.mil
However, both NLSP and IEEE 802.10 have already been strongly influenced
by SDNS!
The Secure Data Network System (SDNS) specifications were released to
NIST in 1989 and have not been significantly updated since. The SDNS
specification for network layer security (SP3 - Security Protocol layer
3) is the basis for the connection-less mode of the ISO Network Layer
Security Protocol (NLSP). The SDNS SP4 (Security Protocol layer 4) is
nearly identical to the ISO Transport Layer Security Protocol (TLSP).
The IEEE 802.10C work was originally using the SDNS Key Management
Protocol as a basis for their key management.
SP3 and NLSP both define a new protocol that can be placed in the
network layer to provide cryptographic encapsulation of other protocols.
The connectionless mode of NLSP was originally nearly identical to the
SP3 specification. The major changes in NLSP from SP3 are:
- The NLSP clear header was modified to make the first octet be
a Protocol ID (PID) that is compliant with the ISO TR 9577
guidelines. Both SP3 and SP4 were defined to share the NSEL of
ISO TP. This NSEL limited placement of SP3 to the top (SNICP)
of the network layer. The Initial PID (IPID) assigned to NLSP
allows it to placed at the bottom, middle or top of the network
layer.
- The SP3-I and SP3-D header encapsulation modes were replaced by
identical functionality that uses the Subsequent PID
(SPID) in the data to determine if IP or CLNP has been
encapsulated. Note that the cryptographic encapsulation of
a complete IP datagram is one approach for subnet-to-subnet
protection.
TLSP and SP4 both added security directly into the ISO Transport
protocol. TLSP differs from SP4 only in the removal of a final sequence
number (SP3 has this feature).
To illustrate how all of these protocols could encapsulate information I
have developed a few examples. First, here are a few examples of ways
that NLSP might operate at the network layer.
a) | link | IP | NLSP-CL | TP or TCP(?) or.. |
b) | link | CLNP | NLSP-CL | TP or IDRP or TCP or ... |
c) | link | IP | NLSP-CL(S-NSAP,D-NSAP)| TCP or UDP or ... |
d) | link | IP | NLSP-CL | IP | TCP or UDP or ... |
e) | link | CLNP | NLSP-CL | CLNP | TP or IDRP or ... |
f) | link | NLSP-CL | any 802.2 SNAP |
g) | X.25 | NLSP-CO | any client protocol of X.25 |
NLSP has two distinct modes of operation connection-oriented (CO) and
connection-less (CL). Much of the ISO specification (DIS 11577) is
unreadable because of the CO mechanism. Ipsec, luckily, only needs the
connection-less mode of operation.
The examples of SP3 encapsulation below are similar to NLSP with two
important differences. First, the model for SP3 places it only at the
top (SNICP) of the network layer. Second, the IP/SP3/IP modes of
encapsulation explicitly define a complete IPv4 header as part of SP3
(the SP3-D mode).
h) | link | IP | SP3-N | TP or ? ... |
i) | link | CLNP | SP3-N | TP or ? ... |
j) | link | IP | SP3-A(S-NSAP,D-NSAP) | TP or TCP or UDP or ... |
k) | link | CLNP | SP3-A(S-NSAP,D-NSAP) | TP or TCP or UDP or ... ? |
l) | link | IP | SP3-D( IP ) | TP or TCP or UDP or ... |
m) | link | CLNP | SP3-I(CLNP ) | TP or TCP or UDP or ... |
As an additional point of confusion one mode of SP3 (SP3-N) is identical
to one mode of SP4 (SP4-E). This commonalty is an artifact of
compromise made to ease the religious wars of layer 3/4 security
placement.
n) | link | CLNP | TP(SP4-E) | ISO Session etc.. |
Some transport layer zealots still feel that SP4-E is viable for ipsec.
I still strongly advocate NLSP as a starting point for ipsec, but at
this early stage it might be useful to examine the encapsulation
characteristics of ipsec.
To provide host-to-host security the following example of ipsec protocol
encapsulation seems reasonable.
o) | link | IPv4 | IPSEC | any client protocol of IP |
p) | link | IPv7 | IPSEC | any client protocol of IP |
Alternatives for IPSEC encapsulation for host-to-subnet and subnet-to-
subnet security include example o & p above along with:
s) | link | IPv4 | IPSEC | IPv4 | any client protocol of IP |
t) | link | IPv4 | IPSEC | IPv7 | any client protocol of IP |
u) | link | IPv7 | IPSEC | IPv4 | any client protocol of IP |
v) | link | IPv7 | IPSEC | IPv7 | any client protocol of IP |
w) | link | IP | IPSEC(S-addr,D-addr) | any client protocol of IP |
Given that proposals exist for installing NLSP directly over IEEE 802.2
the following example is of interest. This application is beyond the
charterUs scope of protecting clients of IP.
x) | link | IPSEC | any 802.2 SNAP |
Recursive cryptographic encapsulation is yet another example to
consider.
y) | link | IP |IPSEC|IPSEC|... | any client of IP including IPSEC |
Finally, we should recognize the suggestions to embed cryptographic
security directly into IPv7.
z) | link | IPv7(IPSEC) | any client protocol of IP |
The only advantage of embedding ipsec into IPv7 would be in saving a few
bytes of header information.
There are more permutations of the examples above, but IUve run out of
letters.
Paul