[cap-talk] How data can you get? A challenge
john.carlson3 at sbcglobal.net
Thu Jan 18 12:23:43 CST 2007
Jed, this isn't taking your challenge, it's merely
commenting on "how data" something can get.
invoke what? A sentence is data with a verb in it.
I'm not sure there's ever going to be an entirely
declarative full protocol, language, or what have you.
UML and OCL? I'd like to see more working examples.
If you're trying to achieve the "key" metaphor,
try creating a lock with pure data. The lock
is part of the object-capability system as well.
What's the difference between this and an HTTPS POST,
given you are using client side certificates?
On Jan 15, 2007, at 10:31 PM, Jed Donnelley wrote:
> How data can you get and still qualify as the purest of pure
> object-capability system?
> This is the topic that I've concerned myself with for the last few
> I believe I've architected (adapted actually) a system that's pure
> data and distributed but is as functionally object-capability as any
> we've discussed (considering implausible guessing to be as likely as
> a hardware failure - i.e. not failure).
> Consider a system in which each active object (process, domain) is
> associated with a public/private key pair. The TCB knows the private
> key (with suitable randomness) and the public key.
> Now consider a capability (by protocol assumption of the TCB) to be
> the following:
> Public key, address hint, data: where "data" is assumed to have a
> sufficiently large section of recognizable data (could be an initial
> block of, say, 128 zero bits) so that it's encrypted form can't be
> The only send operation is "invoke". The invoke operation uses the
> essential procedures in:
> In a diagram:
> In this diagram:
> X <down arrow> indicates the encryption operating with the public
> key and
> X <up arrow> indicates the signing or decryption operation with the
> private key
> In this email message I indicate these as Xd and Xu.
> I now describe the "invoke" operation on a capability that's asked to
> transfer a block consisting of an arbitrary number of data and
> capability 'tokens' (recognizable data blocks, defined by a framing
> convention of the TCB, where each block of data is indicated by the
> framing to be either simple data or a capability).
> 1. The TCB first checks the data block of the capability by applying
> SdXu where Xu indicates the decryption/signing application of the
> domains private key and Sd indicates the encryption/public key
> operation (using the public key that's the first part of the
> capability). If the appropriate recognizable block of data (the 128
> zero bits) isn't in the capability then the invocation fails and goes
> no further.
> Note that in the case that S==X (namely that this is a local object
> and the active object has it's own public key) then this is an
> identity operation that simply checks for the appropriate data
> block. An attempt to send to self fails.
> If the recognizable data block is in the transformed capability then
> the operation continues. In that case it transforms the data block
> of the capability with:
> 2. Sending: The TCB does a nonce handshake with the system at the
> address hint (issues much like with YURLs) to try to communicate
> If that succeeds it continues:
> The communicated message consists of the data blocks that were
> requested to be transferred, untouched. For the capability blocks
> the same operation as in #1 happens for each capability (check and if
> OK transform). Any failure terminates the communication. Otherwise
> the communication continues until either it ends or until any normal
> communication terminating event occurs (network failure, capability
> failure, etc.).
> 3. Receiving: Doing a receive operation requires no capability, but
> receiving can only happen from active objects/domains that have a
> proper capability to the receiving active object. When receiving the
> TCB goes through the dual of the nonce handshake with the public key
> as noted for sending. If that succeeds then it transfers data into a
> receiving buffer with data transferred literally and capabilities
> transformed as:
> In this case X denotes the key(s) for the receiving (local, hence Xu
> is known) domain and Sd is the public key of the sending domain (note
> that in general Sd is different from the server public key). As in
> the sending case, on receiving capabilities are also checked for the
> appropriate redundancy by protocol and rejected if the check fails -
> terminating the receive. In the case where the public key for the
> capability is the same as the public key for the sender, the sending
> address can be checked (a fine point tied into the address hint,
> naming/finding servers, etc.).
> Perhaps I'm just being stubborn about this and I'm missing something
> important, but I don't know of any pure object-capability properties
> that this system doesn't have. In this system the functions of a
> capability TCB and that of a "vat" (e.g. DCCS) are effectively
> I'm very interested to hear any "attacks" on this system. That is
> demonstrations of object-capability functional properties that this
> system doesn't have. There may be simplifications possible and
> certainly optimizations, but I'd very much like to have the
> "object-capability"ness of its functionality attacked.
> Ground rule - Implausible guessing is considered as likely as a
> hardware failure, i.e. not considered in any failure scenario.
> I wonder if an interactive discussion at HP on this topic might be
> worthwhile? I know we had a brief discussion on this basic mechanism
> considered in a different context. Now the keys are maintained by
> the TCB (actually as I suggested in my Managing Domains paper) and
> I'm claiming all object-capability properties.
> If there are simple problems that can be clarified on the list with
> no equally simple fixes (i.e. fundamental), then any such early
> fatality should of course derail any interactive
> discussion. Otherwise I'd be interested in participating in a
> discussion of this topic.
> For me exploring such a mechanism is one way to get at the essential
> aspects of whatever trust is needed in a capability distribution
> mechanism (like the vats).
> --Jed http://www.webstart.com/jed-signature.html
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