the interface hardware and thus is globally unique the 8 th bit from the left is the individual group or u201c g u201d bit which is usually set to 1 for multicast addresses the bit combination u 1 g 1 is currently unused because a multicast address cannot be globally unique the present invention suggests that this bit combination be allocated for cga addresses the present invention may be used even if such allocation is not made however allocating the bit combination for cga use enables mixed use of cryptographically generated and non cryptographically generated addresses in any security protocol without weakening the security of either address type in accordance with the invention the cryptographically generated addresses include the security parameter sec 302 which determines the level of security the security parameter is a 3 bit unsigned integer it is encoded in the three rightmost bits of the 128 bit ipv6 address 314 the security parameter allows the address owner to increase the computational cost of address generation and thus to also correspondingly increase the cost of brute force attacks against the address in effect and as explained in detail hereinafter incrementing sec 302 by one adds 12 bits to the length of the hash that the attacker must break since the security parameter value is encoded into the address bits an attacker cannot change its value without also changing the address with reference to the flowchart of fig4 the procedure of generating a cga begins in earnest with step 404 which is the computation of the second hash value 500 although called the u201c second u201d hash value herein it is actually the first hash value calculated input into the second hash function includes the concatenation of the address owner 39.