Subject: Re: Davis paper revisited // separation of signed and encrypted messages into clearsigned messages

From: <[email-masked]>
Date: Thu, 21 Aug 2003 14:09:12 -0700

On Thu, 21 Aug 2003 13:14:25 -0700 Hal Finney <[email-masked]> wrote:

[...]

>> [1] is there any way to distinguish the composite reconstruction
>forgery
>> from a 'real' de novo clearsigned message ?
>
>I disagree that this is a forgery.  Rather, it is a reformatting

[...]

it is a forgery only in the sense, that if it were, for example, posted
anonymously by someone else,
then there could be circumstances where people viewing it might be upset
that such a message that should have been (and was) encrypted,
was posted as a public clearsigned message.

the term 'forgery' was meant to imply, that the message could be changed
in a way
that did not reflect the intent of the sender, who would never think
of posting it unencrypted.

in a sense, it is the same as the Davis re-encryption, which also does
not reflect the intent of the sender to send it to the third party

but, 

in the case of re-encryption to another receiver, the sender can take
pre-cautions of addressing the 'real' intended receiver by name in the
message plaintext.

while in the case of the clearsigned reconstruction, there is no such

precaution to demonstrate that the sender never intended sending an open

message 
(short of the E,(S&E) solution) 

vedaal

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---

From: Adrian von Bidder <[email-masked]>
Date: Fri, 22 Aug 2003 10:49:23 +0200

[People, why can't you use a sensible mailer who produces In-Reply-To or 
References header?]

...
> of posting it unencrypted.

If you send sensible content to somebody you can't trust to keep it secret, 
there's no technical solution to solve that problem. Don't send that person 
any sensible content - encrypted or not.

If you S/E/S the message, you can still stripp the outer signature and the 
encryption and get a perfectly readable signed message. True, there could be 
some indication that the inner signature was part of a S/E/S message - but in 
the original case, the sender could put a notice 'this is a confidential 
message and was sent encrypted' in the message text.

IIRC E/S/E had some other significant drawback, somebody will certainly point 
it out here, but it would "solve" that particular problem. But I don't think 
that it does achieve more than putting 'this is a confidential message' in 
the signed body:

The recipient can publish the E/S/E message without the outer encryption 
layer. Then he publishes the decrypted message and his public key. Everybody 
can the generate the encrypted message and, with the signature, verify that 
it is the same message. So this "solution" falls apart, too.

cheers
-- vbi

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