On Wed, Mar 08, 2000 at 05:05:24AM +0800, Arrianto Mukti Wibowo wrote:
> Hi,
>
> I want to know whether there is a crypto building block which doesn't allow
> someone to open an encrypted message before a certain date.
>
> [Damn hard. Math functions don't grok "date". The only reasonable way
> to do this without a trusted third party is to pick an encryption
> algorithm that will take at least as long to decrypt (in likely
> available computer time) as are needed. -Perry]
>
> In another word, I need to know several "date/time-related" crypto papers
> around. Can somebody give me pointers?
I don't think it's exactly what you were asking for, but couldn't you
encrypt the data with a session key and then not give the recipient
the key until the certain date?
A related method would be to encrypt the session/bulk key with
a private key who's public key is in a cert which is not valid
until the certain date. At least that way you can send the data
(and encryted key and cert) at once and not require the recipient to
connect back for the key. Unfortunately you're depending on
the cert-verifying software that the recipient uses to
actually enforce the cert's Validity... and current s/w is
notoriously lax on that. Any software solution like
that would be hackable on the recipient's machine.
--
Eric Murray www.lne.com/~ericm ericm at the site lne.com PGP keyid:E03F65E5
