Patent ID: 8438381

Claim:
A method of hiding data within packets of an IP session between first and second hosts which may otherwise be used to link packets of the session, the first and second hosts being attached respectively to first and second access points, the method comprising: using as interface identifier within the source and/or destination address an interface identifier generated using a group key and a host identity, both the group key and the host identity being known to said first host and said second access point, wherein said generation of said interface identifier comprises: generating a pseudo-random number; combining the pseudo random number with said group key using a cryptographic function to generate a pseudo-random interface identifier; and combining said pseudo-random interface identifier with said host identity using an invertible function; maintaining a mapping at said second access point between a network prefix of said first access point, said host identity and a local access network address of said second host; upon receipt of a packet at said second access point from said first host, identifying said group key using the network prefix of the packet source address, and using the group key and the host address to map the interface identifier part of the source and/or destination address to a local access network address; and using said local access network address to forward the packet to said second host.