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From: alt%sri-lanka@sri-tsc.ARPA (E. Howard Alt)
Newsgroups: net.mail.headers
Subject: Re: SMTP source verification.
Message-ID: <316@brl-tgr.ARPA>
Date: Tue, 30-Jul-85 16:27:35 EDT
Article-I.D.: brl-tgr.316
Posted: Tue Jul 30 16:27:35 1985
Date-Received: Thu, 1-Aug-85 05:10:21 EDT
Sender: news@brl-tgr.ARPA
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One good way to do authentication is with encryption of the public
key variety.  The person would encrypt the message with his
private key, and people would decrypt the information with
his public key (carried along with the message) to read the
headers and text.  No one can change the headers of text
of the message, because they can't make ciphertext that will
be decrypted with his public key.  You can't lie about who
sent the message because you wouldn't be able to decrypt the message.

Simple, eh?  The logistics are a bit more complicated...

                                        Howard.