At Sun, 11 May 2014 21:59:12 +0200,
Cyril Soler wrote:
Well, the shared AES key for distant chat is a totally random key that is
valid for a specific
triplet (chat invitation, source, destination). That is precisely what PFS
achieves as well.
PFS needs to do it in a way that is safe to man in the middle attacks. That
is why EDH in Retroshare
for instance uses authenticated diffye Helmann.
When you think about it, the two (SSL+EDH and RS distant chat) are very
similar, but with a
different time frame. Of course, if you keep using the same chat invite for a
long time, it is
similar to not renewing a PFS key during a long session. Not more.
PFS relies on the use of short-lived keys that can't be rederived once
they are discarded. Based on what you've said and what is in the blog
post I'm not yet convinced this is the case. Ideally, I'll find the
time to read the code (if you could point me to the right place, I'd
appreciate it).
What is the problem you are suspecting exactly?
I need to look a the details of RS's distant message protocol to
better convince myself that it satisfies the requirements of PFS.
But, repudiability is, citing the OTR paper, no one should be able to
prove Alice sent any particular message, whether she actually did, or
not. Thus, if Alice signs her messages with her private key, then we
know she sent the message. OTR works around this problem by have a
share private key that both Alice and Bob use to sign their messages.
Thus, Bob knows, by the process of elimination that a signed message
that he didn't compose came from Alice, but he cannot prove to a third
party that a signed message came from him or Alice.
Thanks for the quick response!
:) Neal
On 05/11/2014 09:08 PM, Neal H. Walfield wrote:
I was reviewing the chat service protocol as described here:
https://retroshareteam.wordpress.com/2013/08/08/distant-chat-and-messaging-using-generic-tunnels/
I found the following description a bit worrisome:
Messaging and chat however need confidentiality. Therefore messages
are end-to-end encrypted. This is made possible by two different
mechanisms: distant chat uses a pre-shared symmetric AES key, that
is known only from the two chatting peers. Distant messages are
encrypted using the PGP public key of the destination and possibly
signed by the source.
It seems that RS's chat protocol doesn't PFS or reputability. See the
paper on OTR for details of what this entails:
https://otr.cypherpunks.ca/otr-wpes.pdf
Is this correct? I'd appreciate any clarification!
Thanks!
:) Neal
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