Re: A weakness in PGP signatures, and a suggested solution (long)

[Philippe VIJGHEN <phv@bim.be>]

You are right but the question is: what do you want to sign/encipher,
the message body or the whole message exchange?

We thinked about this when we developed a piece of software
for the European Space Agency which is called EDIDOC server 
(Electronic Data Interchange of Documents).

In our case, SMTP header signing was anyway not acceptable
because we needed to support various communication means.

I won't go into too much details but EDIDOC is acting as 
a central server for information exchange with value added as:
- a clearing house
- security gateway
- communication gateway
- a gateway at document format level
- groupware aspects

Roughly,
- a clearing house:
	everything exchange is logged in the server db

- security gateway
	...this requires of course trusting of the server
	but people with different security packages can send/receive
	 "secured message" (signature, enciphering) to/from
	the server without worrying of the recipient/originator
	configuration. Only the server public key need to be known
	by the partners.

- communication gateway:
	Various ways of transmitting the messages to/from the server
	depending of partner configuration.

	This means that although, as you pointed out, the envelope 
	must be secured itself it can not be the envelope
	specific to the communication method used (SMTP, X.400,...)
	-> usefull information can not be stored at the level
	   of the communication method header (ex. SMTP) but is 
	   included in the secured body (originator, destinator, 
	   timestamp, subject, ....)
	   Only the strict minimal information is included in the
	   SMTP, X.400, FTP, floppy, a.s.o. "headers".
	   Our envelope is structured according to a SGML DTD.

- a gateway at document format level
	Server is doing conformance checking of	documents and
	can even down-translate them based on the recipient
	settings (some will expect SGML, other ones EDIFACT, other
	ones ASCII, other partners WP, .... depending of the
	type of document)

- groupware aspects
	complex scenarios (as chain of approval, document review, ...)
	may be implemented at the server level


For more information, send an e-mail to edidoc-info@bim.be

ESA/ESRIN has some information at http://www.esrin.esa.it

BIM Engineering as a home page (http://www.bim.be) which should
"soon" include information about the server


Philippe VIJGHEN
BIM Engineering Europe