There are a lot of additions being talked about for the remailers, and timestamping is another which could be put in. With commercial PGP coming out, people may soon be doing "real business" using PGP. In this case, timestamps can be a problem. A simple example: you sign an electronic contract with someone. Before signing, you set your date a month ahead. The other person doesn't stop to notice it - many people have trouble translating numeric dates to month names anyway - and accepts the contract. Two weeks later, you revoke your key. He can't enforce the contract because it was made two weeks after your key was revoked. There are plenty of problems which can be caused by modified timestamps. One means of protection would be to have future PGP's detect and warn of postdated timestamps when a signed message is checked. Another would be to use remailers to create trusted timestamps. The remailer would have a key labeled < Remailer xx timestamp >. Timestamped messages would not necessarily be anonymized. There are several ways this could work. You could send a message to a remailer and get back a detached signature certificate. Or the remailer could sign the message and send it on its way. Ideally the remailer would detect a PGP message, de-armor it, sign the .PGP file, re-armor it, and pass it on. This way, PGP would automatically check all the signatures on the received message. You could bounce a message through several remailers and onto its destination, acquiring several timestamps along the way. Or bounce it back to yourself to create a poor-man's copyright. -- MikeIngle@delphi.com
Mike Ingle writes:
There are a lot of additions being talked about for the remailers, and timestamping is another which could be put in. With commercial PGP coming out, people may soon be doing "real business" using PGP. In this case, timestamps can be a problem. A simple example: you sign an electronic
New ideas for "Mom and Pop Timestapping Services" are useful to discuss, but be aware that several papers on exactly this kind of digital timestamping have been presented at conferences, mostly by Stu Haber and Scott Stornetta of Bellcore. Their system involves a hash of some document which is then published in an effectively unchangeable place: the pages of the "New York Times," Sunday edition, form a pretty good "widely witnessed event," to use their terminology. A digital contract timestamped (to the "granularity" of the publishing schedule, clearly) could not easily be disavowed. There are some other details. To reduce storage/publishing requirements, a binary tree of other documents can all be hashed together, so that only a single number need be published. Anyone trying to alter a contract, or to claim the given contract was not in fact timestamped when it was, would have to produce the same hash value with a different input...this can be made intractable with a good hash function. The hash function hides the content of course, so privacy is maintained. Bellcore is offering a commercial service to do this. An Internet service might be exciting (the distribution of NetNews to many thousands of sites, for archiving on CD-ROMs, tapes, etc., is a lot like the "widely witnessed event" of publishing in the "New York Times"). Alternatives to Bellcore may run afoul of patents, though. -Tim May -- .......................................................................... Timothy C. May | Crypto Anarchy: encryption, digital money, tcmay@netcom.com | anonymous networks, digital pseudonyms, zero 408-688-5409 | knowledge, reputations, information markets, W.A.S.T.E.: Aptos, CA | black markets, collapse of governments. Higher Power: 2^756839 | Public Key: PGP and MailSafe available. Note: I put time and money into writing this posting. I hope you enjoy it.
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