[e-lang] [cap-talk] Regarding AMQP Messaging paradigm and pattern in E
kpreid at mac.com
Mon Apr 5 16:42:01 PDT 2010
[Please note crosspost by the original author and me; I propose that
further discussion go to cap-talk unless it is E-specific.]
On Apr 5, 2010, at 17:14, Yuvaraj Athur Raghuvir wrote:
> In Capability based systems (OCAP), the management of capability is
> through explicit exchange of reference - the Granovetter diagram.
> This defines a point-to-point interaction model. In the world of
> messaging, this point-to-point seems to be one case of the possible
> many. Further, it is now becoming important that the messages are
> delivered not on a destination specification but on a pattern based
> specification of the destination. This allows for time independence
> of message creation and delivery.
> Since the AMQP decouples the publisher via the exchange and the
> consumer via the queue, and manages the relation between the
> exchange and queue via binding, I wonder what would be the
> corresponding security pattern in E-Language. In particular, how to
> create a binding between the exchange and queue so that the security
> paradigm is not violated?
Think about 'being a capability system' as a sort of mathematical
structure: it has a set of axioms, and given some definitions the
axioms hold for a given instance (capability system) or not.
Then we can ask, not 'Is this a capability system', but 'What part of
this is a capability system?'
There are two perspectives one can take on message-passing subsystems
1. As component of capability system.
Imagine an AMQP implementation running on top of a capability OS or
VM; consider the 'exchange' and 'queue' (I have only briefly read
about AMQP) as objects inside a capability universe. They receive and
send low-level messages, each having its Granovetter diagram, in order
to implement the AMQP protocol at a higher level. The AMQP
implementation then cannot violate the capability universe, as it
exists within it.
Given this perspective, the question is whether AMQP *is a useful
abstraction* to a capability programmer: are the particular
characteristics it has what you want?
Answering this question tells you whether you can use AMQP as a
component of a capability-structured application.
2. As substrate of capability system.
This is attempting to write capability-structured applications on top
of AMQP. The question here is: does AMQP have the capability
properties? For example, does it deliver messages only to recipients
which were either designated by the sender or previously exercised
permission to listen to some queue/hub/buffer/whateveryoucallit? Does
it permit any participant to delegate authority to any other (that it
has been introduced to)? (This can be worked around by forwarding
proxies, but is undesirable for performance and robustness.)
Given this perspective, the question is whether AMQP can be viewed as
a capability system - is doing so a *completely non-leaky*
abstraction? Perhaps only some subset can be so viewed -- if so, does
use of the excluded portion potentially violate the capability
Answering this question tells you whether you can write capability-
structured applications using AMQP as a general message-passing layer
for the entire application.
Using a message-passing system in *either* of the roles above has some
general requirements: the most significant one I can think of is that
all *identifiers* of objects which may carry authority must be:
1. unforgeable - they are either opaque object references or they
sre cryptographically strong (having enough random bits).
2. undiscoverable - third parties should not be able to get a list
of all the identifiers in the system.
I hope this helps. Please note that I know no more than two minutes'
research on AMQP, and that I am not an expert in capability systems or
their taxonomy and terminology in general.
Kevin Reid <http://switchb.org/kpreid/>
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