Process for establishing a common cryptographic key for n subscribers

Abstract

A process is described which can be used to generate a cryptographic key for a group of subscribers whose number is subject to change. The process can further provide that even after the group key has been established, subscribers can be removed from or added to the key directory without great effort.

1 - 3 . (canceled) 
   
   
       4 . A process for establishing a common cryptographic key for n subscribers using the Diffie-Hellman process, comprising:
 assigning the n subscribers respective leaves of a binary-structured tree which has a root, n leaves, is of depth [log 2 n] and has treenodes;   for each one of the n subscribers, generating a respective secret, the respective secret being assigned to the one of the n leaves to which the one of the n subscribers is assigned; and   establishing secrets consecutively in a direction of the root of the tree for all k nodes of the tree starting from the n leaves of the tree across an entire hierarchy of the tree, wherein two already known secrets are combined using the Diffie-Hellman process to form a new common secret, the new common secret being allocated to a common node so that a common cryptographic key for all n subscribers is allocated to a last one of tree nodes, the last one of the tree nodes being the root of the tree.   
   
   
       5 . The process as recited in  claim 4 , further comprising:
 excluding a selected one of the n subscribers from the tree, the excluding steps including:
 removing a first one of the n leaves of the tree to which the selected one of the n subscribers is assigned; 
 removing a second one of the n leaves, the second one of the n leaves sharing a common node with the first one of the n leaves, the common node with the first one of the n leaves becoming a new leaf assigned to the one of the n subscribers to which the second one of the n leaves is assigned; and 
 starting from the new leaf of the tree in a direction of the root of the tree, establishing new secrets only in those of the tree nodes which lie within a framework of the tree on a path from the new leaf to the tree root.