Gutmann Soundwave Therapy

[Peter Gutmann]

Guus Sliepen <guus at sliepen.org> writes:

>Peter sent us his write-up up via private email a few days before he posted
>it to this list (which got it on Slashdot). I had little time to think about
>the issues he mentioned before his write-up became public.

I should provide some background for the writeup, it started when someone sent
me a link to some VPN software they were using and asked whether it was
actually secure.  I looked at it, found that it was, well, pretty awful, and
told them so.

So they sent me a link to another VPN app.  I had a look at it and it was just
as bad.

By this time it'd turned into an ongoing discussion/attempt to track down some
sort of decent easy-to-use secure-VPN app.  The more we found, the more
discouraged I became.  Initially we'd tried to contact developers but didn't
get much (if any) response, so that towards the end (after getting to the n-th
broken VPN app), to quote the VAX assembler manual, "little sympathy was
extended".  After the initial writeup ended up on Slashdot I did a bit more
googling and found out that some of the problems had been pointed out by
others years before I noted them with no action from the application authors
to fix anything.  This, again, didn't inspire much confidence.

In terms of problems, it wasn't just the homebrew crypto mechanisms, there
were also numerous problems with careless implementations.  One thing that was
very common was to find very little error- or sanity-checking.  Function
return calls weren't checked, critical errors like crypto failures were logged
but the app continued anyway (!!), operations were assumed to have succeeded
at all times, even minor things like checking for an error return with a check
for '== -1' when the function could also fail with a return status of zero (so
only some failures were caught and the code could continue with ininitialised
crypto), the list just went on and on.

>When tinc 2.0 will ever come out (unfortunately I don't have a lot of time to
>work on it these days), it will probably use the GnuTLS library and
>authenticate and connect daemons with TLS. For performance reasons, you want
>to tunnel network packets via UDP instead of TCP, so hopefully there is a
>working DTLS implementation as well then.

I think OpenVPN took the right approach here, they took the part of IPsec that
works well (the ESP transport mechanism) and bolted on the TLS handshake to
replace IKE (DTLS has only appeared quite recently).  They didn't have to
invent their own mechanisms for anything, but took tried-and-tested crypto
mechanisms and code and just went with that.

Peter.

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