1. In a communications system having a plurality of terminal devices (Terminals A to N) coupled to an insecure communications channel (12) over which users of said terminal devices may exchange private messages, each of said user's having a public key (30) and an associated private key (32), an improved method of digitally signing and certifying a message to be transmitted characterized by the steps of:
formulating at least a portion of a digital message (20);
digitally signing said message (40); and
including within said message an authorizing certificate (28, 116) which specifies the authority which has been granted to the signer of said message.

2. A method according to claim 1, further including the step of providing at least one field in said message identifying the nature of the digital data being transmitted (22).

3. A method according to claim 1, wherein the formulating step includes the step of providing a field allowing the user to insert a predetermined comment (26) regarding the data being transmitted.

4. A method according to claim 1, further including the step of applying a hashing function (34) to at least a portion of the message to be transmitted to form a presignature hash (36); and wherein said digitally signing step includes the step of decrypting said presignature hash with said private decrypting key (32) to form said digital signature.

5. A method according to claim 4, further including the step of forming a digital signature packet (42) comprising the digital signature and a representation of said at least a portion of the message to be transmitted.

6. A method according to claim 1, wherein said authorizing certificate (116) defines the cosignature requirements which must accompany the signer's signature.

7. A method according to claim 6, wherein a digital signature by a third party indicating approval of the user's signature is required (116) thereby defining a counter signature requirement.

8. A method according to claim 7, wherein the third party countersigns (86) by digitally signing the sender's digital signature.

9. A method according to claim 6, wherein the step of defining cosignature requirements includes the step of specifying at least one other digital signature which is required to appear in the digital message thereby defining a joint signature requirement (116).

10. A method according to claim 1, wherein said authorizing certificate defines limitations as to the authority granted by the certificate (116).

11. A method according to claim 10, further including the step of setting a monetary limit for the sender.

12. A method according to claim 1, wherein said authorizing certificate includes at least one field indicative of the degree of responsibility delegated to the sender.

13. A method according to claim 1, wherein said authorizing certificate defines a hierarchy of certificates within the transmitted message such that a recipient of the message can verify the authority of the signer based upon an analysis of the signed message.