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.
1. A method for verifying a document belonging to a particular class of documents, said particular class being one of a plurality of classes of documents, each of said classes corresponding to a class encryption/decryption key pair CE,CD, said document incorporating encrypted information E comprising information M derived from said document and encrypted with an encryption E selected from an encryption/decryption key pair E, D and said document further incorporating an encrypted decryption key DE comprising decryption key D selected from said key pair E, D encrypted with encryption key CE; selected from encryption decryption key pair CE,CD associated with said particular class, said method comprising the steps of: a) providing enabling information for enabling retrieval of a decryption key from any document in a selected group of said classes; b) determining if said document is in said selected group, and if so retrieving said decryption key D from said document; c) decrypting said encrypted information E to obtain decrypted information D and deriving said information M from said document; and d) comparing said decrypted encrypted information D.sub.i D with said information M to verify the information contained in said document as authentic and unchanged.