8.3.2 Network layer security

Background:

ISO/IEC 8348, ISO/IEC 8648, ISO/IEC 8880, ISO/IEC 11577, NIST SDNS SP3

NLSP (Network Layer Security Protocol) supports both end-to-end level or subnetwork level security services as depicted in figure B.3 ([FOR94, p.278]). As we are later discussing possible implementations for TCP/IP which uses the connectionless Internet Protocol, we will focus only on the interaction between NLSP and CLNP (ConnectionLess Network Protocol, ISO/IEC 8473).

The network layer can be divided into several sublayers. The amount of sublayers used and the way these sublayers interact has much to do with the complexity of the interaction between different types of underlying networks. For connectionless communication, three types of interaction are relevant from a security point of view:

1.

CLNP headers are not encrypted at all

2.

CLNP headers are partially encrypted (i.e. trusted domain addresses only)

3.

CLNP headers are fully encrypted

  

Figure B.3: Different locations for the NLSP layer

The protection process at the network layer is much the same as that at the transport layer, but some extra data has to be added to cover for services by default not provided by the network layer:

• Sequence integrity (not part of the default network layer protocols, as opposed to the transport layer protocols)
• Traffic padding (the network has to support traffic flow confidentiality, not the transport layer)

The security association identifier is added in clear to the secure network layer data unit. It is interesting to know that routing decisions can be affected through the use of labels in ISO CLNP and Internet IP protocols.