RE: [Asrg] 6. Proposals - Challenge/response - CRI

["Eric Dean" <[e-mail]>]

Yes considering many CR systems use CR URLs such as
http://cr.foo.com/?sender=[e-mail]&rcpt=[e-mail]

There's a lot of room for improvement.

> -----Original Message-----
> From: [e-mail] [mailto:[e-mail]] On Behalf Of
Deven
> T. Corzine
> Sent: Wednesday, August 20, 2003 1:42 PM
> To: Yakov Shafranovich
> Cc: Andrew Akehurst; [e-mail]
> Subject: Re: [Asrg] 6. Proposals - Challenge/response - CRI
> 
> On Wed, 20 Aug 2003, Yakov Shafranovich wrote:
> 
> > > > I think the only really significant semantic suggestion I'm
making
> > > > is that a hash of the body of a message should be included to
> > > > prevent forgeries of level-two systems.
> >
> > That has been mentioned before and is a pretty good idea. It also
> > alleviates some privacy concerns since the originating MTA/MUA does
not
> > have to store copies of messages, but can store MD5 hashes instead.
> 
> Using a hash is an obvious thing to do, but it begs the question of
> exactly
> what you're hashing.  You can't safely hash the entire message because
the
> headers change on every hop, at least for Received: lines.  Other
headers
> might be mangled or normalized as well.  You can ignore the header,
but it
> would be good to validate parts of it.  Even if you just hash the
body,
> you
> have to be concerned about the message being mangled by intermediate
MTAs.
> 
> Now, you could Base64-encode the content to protect it against
mangling,
> but that renders the plaintext of the message unreadable.  You could
strip
> out all characters but the ones used for Base64 encoding, and hash
that.
> Perhaps quoted-printable encoding would be another semi-readable
option.
> 
> PGP has to deal with this issue for "clear-signed" messages -- how
does it
> address this issue?  (Or does it depend on the body not getting
mangled to
> be able to verify the signature?)
> 
> Of course, another option is to simply use PGP.  This seems the
obvious
> answer for mailing lists -- the mailing list should clear-sign all
valid
> messages with a private key used only for that mailing list, and have
the
> user whitelist that PGP key (perhaps by keeping a copy signed with
their
> own PGP key?) -- then no spammer could forge messages appearing to be
from
> that mailing list...
> 
> Deven
> 
> 
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