20. An apparatus as described in claim 15 wherein said enabling means further comprises a memory means for storing a plurality of said preselected keys CD, and wherein said enabling information comprises information defining a group of said decryption keys CD corresponding to said selected group of classes; said apparatus further comprising means responsive to said enabling information for storing said group of decrypting keys in said memory means.
15. An apparatus for verifying a document belonging to a particular class of documents, said particular class being one of a plurality of classes of document, 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 key E selected from an encryption/decryption key pair E, D and said document further incorporating encrypted decryption, key CE comprising decryption key D for said key pair E, D encrypted with encryption key CE selected from class encryption/decryption key pair CE, CD associated with said particular class, comprising: a) means for scanning said document to input scanned information, said scanned information including said encrypted information E, said encrypted decryption key CE, and information identifying said particular class; b) means responsive to enabling information for enabling retrieval of a decryption key from any document in a selected group of said classes of documents and responsive said identifying information to determine if said document is in said selected group, and if so retrieving said decryption key D from said scanned information; c) means for decrypting said encrypted information E from said scanned information to obtain decrypted encrypted information D; and d) means for comparing said decrypted encrypted information D with said information M to verifying the information contained in said document as authentic and unchanged.