From: Bill Stewart <stewarts@ix.netcom.com>
Date: Fri, 8 Dec 95 14:34:17 PST
To: Mark Twain Ecash Support <support@marktwain.com>
Subject: Re: Still more on the Digicash protocol
Message-ID: <199512082234.OAA02297@ix9.ix.netcom.com>
MIME-Version: 1.0
Content-Type: text/plain


At 12:26 PM 12/8/95 -0600, Mark Twain Bank Ecash Support wrote:
>>There's no need to send that payment info in the clear -- why not encrypt?
>
>DigiCash agrees that it is desirable to encrypt the payment request. The
>problem is how? You can't use the payor's public key, since the payor is
>anonymous to the payee. There are other, high overhead, protocols that might
>be used, but after taking MIM into account, securing the payment request
>from within Ecash while retaining acceptable latency is much harder to
>acomplish than one might think. 

Obviously if the payer is the one transmitting the message, she doesn't
use her public key to encrypt; hers would be used for signature if appropriate.
She should use the payee's public key, or some negotiated key like DH.
It doesn't lose any privacy, because she already knows an address to send
the money to, and the payee can create a public key for that address,
or some other public key he makes available to payers.

>The best solution at this time seems to be to use the already existing https
>connection to transmit the payment request. The next version of Ecash will
>offer this feature as an option to the user.

I had assumed that the payment information wasn't encrypted because that's a
separate problem from the basic digicash, and because if the payer wants
to keep the transaction private, she probably also needs to encrypt the
other side
of the transaction - e.g. the request for n widget at $d/widget.
https or other ssl connection, or an encrypted telnet, or encrypted email,
or some other protected mechanism all would seem to be appropriate.
#--
#				Thanks;  Bill
# Bill Stewart, Freelance Information Architect, stewarts@ix.netcom.com
# Phone +1-510-247-0663 Pager/Voicemail 1-408-787-1281

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