A method for formation of a shared secret key using a key matrix and a
corresponding authentication protocol are described. The shared secret
key formation scheme is a method in which sets of secret device keys are
formed from arithmetic operations on matrix keys of a key matrix. The
contents of the key matrix are held in confidence by the certification
authority. The selection of which matrix keys to use is based on a key
selection vector assigned by the certification authority. From the secret
device keys, a shared secret key may be formed in accordance with a
selected authentication protocol.