-----BEGIN PGP SIGNED MESSAGE----- Digital signatures can have many different uses and meanings. The most popular application of digital signatures is proof of authorship. A person signs something when he claims that he wrote it and if the signature is invalid, the message must have been altered. However, digital signatures are used for many other applications. Typical applications include timestamping, digital cash, and validating a document or statement. The problem with these applications is that there must be some way to distinguish and timestamp signature from a proof of authorship. There are several different ways to do this: - Make all digital signatures prove proof of authorship. Someone would include the text of the document he wants to sign and put a message saying at the end such as: "This document existed on such and such date" or, in the case of digital cash, "This coin was blinded and signed by the bank using standard protocols." - Append some kind of electronic tag to the message that represents a certain kind of authorization. This is identical to the previous method except it relies more on protocols. - Specify the type of signing that is to be done with a key. This could be included in the text of the user-ID field of the public key in a PGP-like program. It could also be done by extending a key generation and management protocol to include a tag on the key itself specifying what this key is to be used for. There are advantages and disadvantages to each of these. The first has the advantage that it requires no protocol modification but relies on "legaleese." The second method does require that protocols be slightly modified, but these modifications could be made by just pre-processing and post-processing the message with another program. However, this is more limited than the first method because it essentially uses "canned" messages. The final method relies on either no modification to the crypto program used or a non-trivial modification. Personally, I tend to think that anything that uses a standardized protocol is a Good Thing. This is why I think that the second and third methods listed above would work better than the first. Comments? - --Mark =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= markm@voicenet.com | finger -l for PGP key 0xf9b22ba5 http://www.voicenet.com/~markm/ | bd24d08e3cbb53472054fa56002258d5 PGP: Because sometimes, a _Captain Midnight_ decoder ring simply isn't enough. -----BEGIN PGP SIGNATURE----- Version: 2.6.3i Charset: noconv iQCVAwUBMQ1agLZc+sv5siulAQFKtwP/Xs7gOm1vP2FeDJDjahymYbMum3JrFqh0 VKXrkjmlh42ygX9y2sLfivN7DMsAGIF86NRaW67x0LD2uPuBl00KyvC18bqEPfiF kMbvOZv96xL4fBssheRR7F4YH/oaASxCagxuAkIqBxi9uEzAppNloxMYHy87w0kY h+48n+YH3D0= =QTZp -----END PGP SIGNATURE-----