2. A method as described in claim 1 further comprising the step of: a) providing verifying means for receiving said enabling information and for decrypting said encrypted information E, said verifying means further comprising memory means for storing preselected decryption keys CD, said preselected keys CD being in one-to-one correspondence with said classes, and still further comprising means responsive to said enabling information for enabling said verifying means to access selected groups of said preselected keys; and wherein, b) said enabling information comprises information defining a group of said preselected keys CD corresponding to said selected groups of classes.
2. A method as described in claim 1 further comprising the step of: a) providing verifying means for receiving said enabling information and for decrypting said encrypted information E, said verifying means further comprising memory means for storing preselected decryption keys CD, said preselected keys CD being in one-to-one correspondence with said classes, and still further comprising means responsive to said enabling information for enabling said verifying means to access selected groups of said preselected keys; and wherein, b) said enabling information comprises information defining a group of said preselected keys CD corresponding to said selected groups of classes. 3. A method as described in claim 2 wherein said enabling information comprises a code word, the bits being in one-to-one correspondence with said preselected keys CD, said verifying means storing said code word and said enabling means responding to said code word to enable access to one of said preselected keys if and only if a corresponding bit of said code word is asserted.