1995-11-08 - expiration dates on cryptography

Header Data

From: John Curtis <jbell@capecod.net>
To: “‘cypherpunks@toad.com>
Message Hash: 1822f6b8af1776ac1915ed69180f7391eb0fd0e5126184143ba33fdef4fa6494
Message ID: <01BAADAA.DFB5F740@hy36.capecod.net>
Reply To: N/A
UTC Datetime: 1995-11-08 12:31:36 UTC
Raw Date: Wed, 8 Nov 1995 20:31:36 +0800

Raw message

From: John Curtis <jbell@capecod.net>
Date: Wed, 8 Nov 1995 20:31:36 +0800
To: "'cypherpunks@toad.com>
Subject: expiration dates on cryptography
Message-ID: <01BAADAA.DFB5F740@hy36.capecod.net>
MIME-Version: 1.0
Content-Type: text/plain

The discussion between Mr. May and Mr. Shields concerning
time-release cryptograhy raised an interesting question in my 

Given that trust is often of an ephemeral nature, it would be
quite useful to set time limits on secrets.  Would it be possible
to cryptographically protect a secret such that it could not be
decrypted after a certain time?

I suspect that the laws of thermodynamics might prohibit this
in classical cryptography because as a message expired the 
amount of entropy would decrease.  Quantum cryptography
might work, but that will be science fiction for some time to

Has anyone either shown how to do this or proven it impossible?