Re: [Monotone-devel] netsync transport encryption?

[Ulf Ochsenfahrt]

Jeronimo Pellegrini wrote:
> If you can label computers as "trusted" and "posibly hostile", then
> you can encrypt the database -- and never checkout or have the
> clear version on the hostile hosts. You would only decrypt it in trusted
> hosts where you'd keep your workspace. A solution based on
> communication encryption works also, but then you would have
> all hosts as "possibly hostile". It depends on your needs.
>
> My point is that if you encrypt the database, encrypting the channel
> is not necessary (because the diffs are sent encrypted already), and
> you can use plain netsync.

Not true. Encrypting the database and encrypting the channel solve 
different problems. And encrypting the database isn't the golden bullet 
you seem to assume it to be.

If you put an encrypted database on an untrusted host, you still have 
several problems:
1. the host knows that there is a database
2. the host can log all communication in both directions
3. the host can corrupt the database

Encrypting the connection helps against accidental or willfull 
evesdroppers. (Though they still know that you did communicate.) If you 
don't encrypt the connection, evesdroppers also know:
1. what you do (monotone sync)
2. how many revisions
3. revision ids

And then there's authentication. monotone already authenticates users so 
 you can disallow (or allow) certain users to read and/or write from 
the database.


There are also problems with citing Bruce Schneier's "Applied 
Cryptography". Mr. Schneier himself has actually called mixed feelings 
about that book (go read "Beyond Fear" if you don't believe me).

Now, I've got Applied Cryptography as well, and I have Beyond Fear and 
Secrets and Lies, and I've actually read them. ;) The problem I see with 
encrypting the database or the connection is that it's so damn easy to 
make just a tiny programming mistake and fuck everything up (see ssh for 
example). And then for the sake of backwards compatibility, you have to 
keep it that way. For an encrypted connection, I'd much rather trust ssh 
and/or ssl tunnels. ssh/ssl has had a lot of eyes looking at it, which 
you can see from the fact that security issues _have_ been found.

That said, I am against having connection encryption (and all its 
overhead) in monotone. (On a side-note, I'd find it good if monotone 
could use gpg for signing and authentication. gpg is well-known and 
well-looked-at. Of course, it would add an external dependency, 
unfortunately.)


Cheers,

-- Ulf

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