Patent ID: 7660417

Claim:
A method of enhancing security for protected communication based on a key agreement procedure in a mobile communications network having a network side for serving a mobile terminal having at least one basic cryptographic security algorithm, said method comprising: said mobile terminal transferring a list of at least one enhanced version, supported by said mobile terminal, of said at least one basic cryptographic security algorithm to said network side; said network side selecting an enhanced version of said at least one basic cryptographic security algorithm for communication between said mobile terminal and said network side based on said list of at least one enhanced version, supported by said mobile terminal, of said at least one basic cryptographic security algorithm and a list of at least one enhanced version, allowed by said network side, of said at least one basic cryptographic security algorithm; said network side transmitting information representative of said selected enhanced version of said at least one basic cryptographic security algorithm to said mobile terminal; said mobile terminal generating an algorithm-specific security key by applying a basic security key resulting from said key agreement procedure and said information representative of said selected enhanced version of said at least one basic cryptographic security algorithm as inputs to a key-modifying function which generates said algorithm-specific security key based on said basic security key and said information applied as inputs; and said mobile terminal applying said algorithm-specific security key as key input to said at least one basic cryptographic security algorithm for protected communication between said mobile terminal and said network side of said mobile communications network, wherein said at least one basic cryptographic security algorithm together with said algorithm-specific security key correspond to said selected enhanced version of said at least one basic cryptographic security algorithm, and wherein both said basic security key and said algorithm-specific security key are valid for protected communication between said mobile terminal and said mobile communication network.