[OTR-dev] Flaw in OTR Protocol (with workaround!)

Andrew Rodland arodland at entermail.net
Wed Aug 3 15:08:23 EDT 2005

On Wednesday 03 August 2005 02:44 pm, Ian Goldberg wrote:
> On Tue, Jul 26, 2005 at 08:39:01AM -0400, Greg Troxel wrote:
> > I'd like an OTR implementation to be able to send a computer-readable,
> > authenticated "delete SA" message to the other side, for example when
> > exiting a client.
> It was a design decision very early on that there be no way for a client
> do drop from "private" to "not private" except if the user explicitly
> requests it.  Imagine you were typing some long private message to your
> buddy, and just before you push "Enter", your client receives this
> "delete SA" message.  We do *not* want your private message to be sent
> unencrypted!

I still think that it would be useful, to prevent the case where I restart my 
client (or go away for a day), implicitly resetting my session, while my 
buddy stays online, and later sends me an encrypted message I can't read. How 

1. Alice sends "End Session" request and tears down her session. No further 
confirmation is needed on her end because she initiated the privacy drop.
2. Bob receives notification that Alice has ended the session, and is asked to 
confirm his awareness of this [1].
3. Any messages that Bob sends to Alice before confirming the end-of-session 
are discarded by OTR, and OTR sends a further reminder status message.

[1]: This could be done with a status message and challenge/response thing, 
i.e. "Alice12345 has ended the secure session. Please type OTR2i94hd to 
confirm.", or by hijacking the OTR privacy widget on clients that have it; a 
status message is produced and the widget changes from "OTR: Private" to 
"OTR: Locked"; clicking the widget changes it to "OTR: Not Private".

-- Andrew Rodland
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