Authenticating distributed Ruby

[Trejkaz]

Hi all.

I've been playing with DRb a fair bit lately, am planning to use it as
part of a Rails-to-XMPP integration project. XMPP is relatively costly
to authenticate with, and one of the ways around that is to login only
once and then have every Rails instance talk via DRb to that single
instance. And of course the other benefit of having the clients online
24/7 is that it would allow me to affect the state of my application
and give live feedback via XMPP messages and commands.

Of course, DRb in itself provides no real security. But because of the
nature of some of the applications I want to make possible, I do want
to provide some basic protection against some of the more obvious kinds
of attacks which occur.

The first aspect of this is encrypting the traffic which I can use SSL
for. Although I'm not particularly keen on having to generate a
certificate just to run this lightweight server... some lighter
encryption would be preferable but I'll take what's available. Once I
have SSL up, at least I can assume that people won't be able to spy on
the messages which are being sent back and forth.

The next aspect is some kind of basic authentication. Really, what I
want is just a secret key that the client has to pass in in order to
get access to my remote objects. But, I don't want to have to add that
secret key to every method.

One idea I came up with, which is simple but probably not very good:

class Chest
def initialize(treasure, key)
@treasure = treasure
@key = key
end

def unlock(key)
if @key == key
return @treasure
else
return nil # I suppose an exception would be better.
end
end
end

Then I serve the Chest instance up as the remote object, and this way
the "real" server (the treasure) doesn't have to have the password
added to all its methods, but I get an icky feeling that it opens the
door to someone somehow "remembering" the remote reference to the
treasure and getting a direct reference to it somehow after the
password is changed.

How do people usually do this sort of thing? Is there a
generally-accepted norm?

TX

 

[Justin Meyer]

Hi Gregory, Trejkaz:

]
} The next aspect is some kind of basic authentication. Really, what I
} want is just a secret key that the client has to pass in in order to
} get access to my remote objects. But, I don't want to have to add that
} secret key to every method.
[...]

You may find the following URLs helpful in understanding and implementing
this:

http://www.freebsddiary.org/openssl-client-authentication.php
http://www.mindreef.com/support/soapscope/4.1/help/sslcerts.html
http://www.pseudonym.org/ssl/ssl_cook.html

} TX
--Greg

For specifically doing DRb over SSL, with client cert-based auth, this
URL might also be useful:

http://segment7.net/projects/ruby/drb/DRbSSL/

 

[X-Man]

The next aspect is some kind of basic authentication. Really, what I
want is just a secret key that the client has to pass in in order to
get access to my remote objects. But, I don't want to have to add that
secret key to every method.

If your communications is of the (essentially) non-connected variety,
example being HTTP, I don't see getting around passing an access "key"
with each call.

I think "the way" involves a process like this:
- client requests a salt from the server
- server leases a salt to the client (good for 20 minute, for example)
- the client hashes the password, adds the salt to that, and hashes it
again
- the client sends this to the server with each request, along with the
salt used
- the server checks that the salt is not expired
- the server verifies the hash-salt-hash using the same hash-salt-hash
algorithm

We've used this basic procedure on several systems. It's pretty good.
The hashing we use is the 128-bit MD5 hash.

 

[Trejkaz]

If your communications is of the (essentially) non-connected variety,

example being HTTP, I don't see getting around passing an access "key"
with each call.

Well, this depends on how you look at HTTP.

In the case of Rails, the majority of deployments seem to use FastCGI,
which keeps its instances up 24/7. Those instances could easily stay
connected to the DRb server as long as there is some way to
authenticate when they first connect. I'm fine with having to
authenticate for each connection, which is what my above solution was
all about (of course, it was only concept... a proper version would, as
you say, use a session ID and hashing to authenticate so that even if
someone snooped the conversation, they wouldn't get the real password.)

What I'm more worried about is whether a connection could connect, get
a reference to the remote object, disconnect, and then connect and
without authenticating, forge a direct method call to the object they
remembered from before.

It's almost like the hash which contains their password needs to be
used as part of the remote ID mapping. That would be one way to
prevent this sort of memory, though I'm not entirely sure how to go
about it (YET... I've been reading drb.rb a lot lately. ;-))

I did get authentication working using SSL client certs last night,
generating them with QuickCert which is, BTW, extremely nice for this
sort of prototyping work. But the problem is that as far as I can
tell, my remote object can't determine which client certificate was
passed in. So it's nice and simple for authentication, as long as you
want every connection to have access to everything. But maybe that's
okay for now.

TX

 

[Eric Hodel]

I did get authentication working using SSL client certs last night,
generating them with QuickCert which is, BTW, extremely nice for this
sort of prototyping work. But the problem is that as far as I can
tell, my remote object can't determine which client certificate was
passed in. So it's nice and simple for authentication, as long as you
want every connection to have access to everything. But maybe that's
okay for now.

You'll have bigger problems than authentication if you want to have
different access levels. The ability to create a DRbObject gives you
a reference to any object in the remote process.

NamedIdConv instead of the default DRbIdConv may be of assistance,
but it would take some significant thought to be sure.