-----BEGIN PGP SIGNED MESSAGE----- Earlier, L. Detwiler posted a message which listed some desirable properties of digital signatures. (I won't comment on the rest of the post since I'm behind in list mail and haven't read up). Signatures (real and digital) ideally have the following properties, and maybe others: 1) Unforgeable. The presence of the signature shows the signer attached it on purpose. Also, the signature should convince another party that the signer signed the document (i.e. the signature can be linked to somebody or a pseudonym or whatever satisfies the recipient). 2) Not transferable. If the signer signs one document, it should be impossible to transfer the signature to another document. (Beware signing random documents - see a previous post on the "Notary Protocol" or Judith Moore's paper on protocol failures). In the digital world, transfering a signature should make it invalid. 3) Can't repudiate. The signer can't claim he/she did not in fact sign a document which bears the signature. 4) Can't alter. A document which is signed can't be altered without invalidating the signature. I don't know if a signed contract with white-out, strike-outs, and various inserted edits is still valid, but a good digital signature should contain information (secure cryptographic hash like md5, md4, snefru, snefru256, etc.) about the text signed. For instance, PGP and RIPEM signatures contain an md5 hash of the message text, so altering the document after it's signed will invalidate the signature. -----BEGIN PGP SIGNATURE----- Version: 2.3a iQCVAgUBLMxYWoOA7OpLWtYzAQHARQQAm9m28LRxWWXMeCDN9uNvTc58+4vndkpZ +2VCAGQ5x4EMYOCWCWV81+kJ3qHS6lXZ3crpRONCcXINi58tB4+mr+XWEKsB98Ms 1C5yCS8P+jGMREq4RNiNWf+LNS4oMXtMi/66a0ytEHvNE5v8vYgOsM14FYe5fQ/u wmorJXkuetE= =OSlu -----END PGP SIGNATURE-----