[cryptography] cjdns review

Natanael natanael.l at gmail.com
Thu Oct 4 17:07:30 EDT 2012


AFAIK the key is just generated once and then hashes are generated in two
rounds, if it is 0xFC at the first try it's done, otherwise it runs more
checksum rounds in groups of two.
Den 4 okt 2012 22:55 skrev "Guus Sliepen" <guus at sliepen.org>:

> On Thu, Oct 04, 2012 at 02:37:53PM +0200, Eugen Leitl wrote:
>
> > I've recently become interested in cjdns
> http://en.wikipedia.org/wiki/Cjdns
> > which apparently used NaCl in UDP over tun when tunneling.
> >
> > I'm not aware of any review of the entire system, including
> > key generation etc.
>
> Disclaimer: I only read the Wikipedia article and the whitepaper.
>
> It is very interesting, they use the hash of a public key as the address
> of a
> node. That reminds me of SILC. There is some cost involved in claiming an
> address; one must generate 128 EC keys one average, since the first byte
> of the
> address must always be 0xFC in order to be a valid IPv6 address without
> conflicting with public addresses.
>
> If you know which node you want to talk to, both peers first generate
> ephemeral
> keys, which are signed and encrypted using NaCl's crypto_box() function.
> Then
> these ephemeral keys will be used to encrypt the real data packets, but
> again
> using crypto_box(). That means asymmetric crypto is used for every packet,
> which makes it VERY slow.
>
> Not only that; apart from end-to-end encryption and authentication,
> packets are
> also encrypt+authenticed hop-by-hop (unless the peers are direct
> neighbors).
> Given that it is also possible to do a limited form of source routing, this
> might make it robust against traffic analysis and increase anonimity, but
> it
> adds a large burden to intermediate nodes. It also goes against the
> Internet's
> principle of a dumb core with smart edges.
>
> I do not see an obvious flaw in the key generation, encryption and
> authentication. But in the end, you are not going to remember 120 bit
> addresses, so currently they are just running DNS on top, I guess that is a
> very weak point in cjdns.
>
> Another issue might be the routing table itself; the whitepaper doesn't
> mention
> much, but the Wikipedia page say they use a DHT similar to Kademlia. I do
> not
> know how well that can route around "damage" or malicious nodes.
>
> --
> Met vriendelijke groet / with kind regards,
>       Guus Sliepen <guus at sliepen.org>
>
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