Legal interception of encrypted IP traffic

摘要

A method of facilitating the legal interception of an IP session between two or more terminals I,R, wherein said session uses encryption to secure traffic. The method comprises storing a key k allocated to one of said terminals I at the terminal and at a node TTF within a network through which said session is conducted. Prior to the creation of said session, a seed value 'Nonce' is exchanged between the terminal I at which the key is stored and said node TTF and a security function PRF( ) is applied to the key and the seed value at both the terminal I and the node TTF to generate a pre-master key k_m. The pre-master key also becomes known to the other terminal R involved in the IP session. The pre-master key is used, directly or indirectly, to encrypt and decrypt traffic associated with said IP session. The traffic may be intercepted using the pre-master key available at the node TTF. The security function is preferably a pseudo-random function. Terminal R may provide a second seed value and the security function may be applied to both seed values.