In an embodiment, a method for generating and distributing keys retains the scalability of a group VPN, but also provides true pair-wise keying such that an attacker who compromises one of the devices in a VPN cannot use the keys gained by that compromise to decrypt the packets from the other gateways in the VPN, or spoof one of the communicating gateways. The method is resistant to collusion when co-operating attackers overtake several VPN gateways and observe the keys stored in those gateways. In an embodiment, a VPN gateway comprises a cryptographic data processor configured to encrypt and to decrypt data packets; group key management logic; and Key Generation System logic. In one approach a gateway performs, in relation to adding a group member, receiving in a security association (SA) message secret data for use in the KGS; and derives keys for secure communication with one or more peer VPN gateways using the secret data.