[DGD] capability based security?
bart at wotf.org
bart at wotf.org
Wed Mar 23 18:10:23 CET 2016
That is a good general definition for
subjects in this context, the difference I
pointed out is based on what kind of
subjects make sense for permission versus
capability based systems.
A traditional permissions based system
requires subjects to be users or represent
users. A capability based system can be
based on those but doesn't have to. In a
permission based system you run a process in
the name of a user (principal) whereas in a
capability system you give a token to said
process. That can be based on the user for
whom this is running but doesn't have to.
A practical examples:
Lets assume we have some program which
requirrs access to a specific file.
- permission based: you grant permission to
said file to the user under whoms identity
the program has to run. Consequently, every
process running for this user can access the
file.
- capability based: you grant the capability
to the specific process. This may but does
not have to be related to the user under
whoms identity this runs. Consequently only
this process gets the access.
First of all, capability based means you
have something based on least privileges,
and second, it is based on what needs to be
done. You lose both attributes at least
partially as soon as you regard users as
subjects in a capability based system.
Bottomline, you indeed have subjects on one
axis regardless of what system you
implement, but a capability based system can
have subjects which don't work for a
permission based system, whereas a
permission based system requires subjects
which are limiting for a capability based
one.
And as a consequence, the actual matrices
for permission and capability based systems
should differ in what is on the subject axis
besides which axis is used for slicing it.
Actually proving a security system requires
an implementation, so it is a bit surprising
this isn't really part of such papers. How
can one design and implement a security
system without demonstrating how it results
in a safe state?
Bart
On Wed, 23 Mar 2016 23:49:06 +0800, Carter
Cheng wrote
> Actually based on the general literature I
have always viewed
> subjects as any entity about which one
wants to know whether it can
> be granted access or not to a given x via
a security matrix lookup.
> This is kind of what I meant by the
definition. I.e. it could be a
> set of almost anything that you want to
make this query about.
>
> I think for the papers in the areas of
capabilities and permissions there
> tend to be very few actual serious proofs
in the papers I've encounter.
> They mainly describe the implementation
details of the specific realisation
> of the basic principles.
>
> As this paper mentions-
>
>
http://citeseerx.ist.psu.edu/viewdoc/downloa
d?doi=10.1.1.112.8296&rep=rep1&type=pdf
>
>
<http://citeseerx.ist.psu.edu/viewdoc/downlo
ad?doi=10.1.1.112.8296&rep=rep1&type=pdf>
>
> The problem of administration is a
fundamental problem with practical
> capability systems- I am not sure how
practical they really are
> since they don't have much of a great
presence outside the research
> setting. The burden placed on a mud admin
might be quite great given
> that many of the ones I have known aren't
necessarily that
> technically inclined.
>
> Regards,
>
> Silenus.
>
>
<http://citeseerx.ist.psu.edu/viewdoc/downlo
ad?doi=10.1.1.112.8296&rep=rep1&type=pdf>
>
> On Wed, Mar 23, 2016 at 6:16 PM,
<bart at wotf.org> wrote:
>
> > Well, Shentino is trying to build a
> > practical system, and I am looking at
actual
> > implementations that have seen use in
the
> > real world outside a pure research env.
> >
> > The definition of subject is highly
relevant
> > for proving the security of a system,
even
> > more so within the context of an lpc
> > environment which has no concept of
process,
> > but in case of dgd can offer persistent
> > subjects which are not based on a
principal.
> >
> > Because the things you can prove about a
> > capability based system strongly depend
on
> > how you define those subjects, its
certainly
> > much more then the implementation choice
you
> > suggest.
> >
> > This is also documented in various
papers
> > and for example one of the fundamental
> > considerations behind eros.
> >
> > Bart
> >
> > On Wed, 23 Mar 2016 17:01:39 +0800,
Carter
> > Cheng wrote
> > > I actually was just quoting a textbook
> > description by I believe Tanenbaum.
> > > I suspect that what is defined as a
> > subject is an issue of implementation
> > > rather than theory. Whether the
subject is
> > a process itself or an
> > > individual user is mainly a matter of
> > definition from a theoretical
> > > perspective since the matrix is
> > fundamental to descriptions of security
> > > even in the research literature. From
this
> > perspective the smallest element
> > > typically is similar to what raymond
is
> > describing which is kind of the
> > > associate action that can be taken S x
R x
> > A matrix. In the case of the
> > > implementation of the security matrix
I
> > sort of agree. However if
> > > you look at some capability based
research
> > systems a fundamental
> > > element most such systems is transfer
of
> > the socalled key.
> > > Revocation is known to be problematic
in
> > capability based systems
> > > but not impossible. For many
> > implementations it is however quite
> > > difficult given how the key is
> > represented.
> > >
> > > >From a more practical standpoint the
> > number of such elements is quite
> > > large. So the data denoting the
various
> > "keys" can be difficult to manage.
> > > I think from a practical standpoint in
a
> > dgd based system one has to
> > > decide
> > > (practical issue) what the subjects
are
> > and how to cope with revocation
> > > under transfer. My sense is ideally it
> > should be closed under a kind
> > > of transfer operator in a transitive
> > manner i.e. if A gives a copy
> > > of a key to B and B then gives a copy
of
> > the key transferred in this
> > > manner to C. If A subsequently revokes
B's
> > key C should be revoked
> > > as well unless it was transferred to C
by
> > some other source as well.
> > > This kind of management might require
> > somewhat complex book keeping
> > > however and also might have unforeseen
> > consequences when one isn't
> > > exactly sure of the history of
transfers
> > when doing a revocation.
> > >
> > > There are probably a number of
research
> > papers describing research systems
> > > out there that one could look at for
some
> > examples.
> > >
> > > Regards,
> > >
> > > Silenus.
> > >
> > > On Fri, Mar 18, 2016 at 6:13 PM,
> > <bart at wotf.org> wrote:
> > >
> > > > In a more general sense,
capabilities
> > are a way to grant a privilege to a
> > > > subject, which does not depend on
> > listing all allowed subjects on the
> > > > target,
> > > > but rather on giving the subject
some
> > kind of token that can be verified by
> > > > the target.
> > > >
> > > > It assumes this token cannot be
forged
> > and can be verified reliably. Being
> > > > able to transfer a capability is
often
> > but not always part of this.
> > > >
> > > > An important distinction between
> > permission based systems and capability
> > > > based
> > > > systems is a permission based system
> > requiring a subject for a privilege
> > > > to be
> > > > linked to a principal (user),
whereas a
> > capability system does not, a
> > > > subject
> > > > can be a single process, or program,
or
> > object, without any relation to a
> > > > specific user. Due to this, the
approach
> > that capabilities and permissions
> > > > are
> > > > just 2 different ways to slice up
the
> > security matrix is at least
> > > > incomplete,
> > > > and in many cases incorrect. A
> > permission based system has subjects
based
> > > > on
> > > > principals on one axis, whereas a
> > capability based system shouldn't,
> > > > rather,
> > > > it should have subjects based on the
> > smallest entity in the system which
> > > > can
> > > > still use a privilege (usually a
> > process, but this could be a single
> > > > program,
> > > > or part of a program, ie, a single
> > function)
> > > >
> > > > Bart.
> > > >
> > > > On Thu, 17 Mar 2016 17:06:00 -0700,
> > Raymond Jennings wrote
> > > > > I think capabilities are this:
> > > > >
> > > > > Subject X (a user, or a process
> > associated with a user) can possess a
> > > > > capability Y (read, write,
execute, or
> > other such access) for object
> > > > > Z (a file, a user, a process).
> > > > >
> > > > > A privileged process W creates the
> > capability Y and gives it to
> > > > > subject X once X proves it has
> > authorization (presenting a password,
> > > > > authenticating, or even in some
cases
> > picking up another capability),
> > > > > and then X can freely use
capability
> > Y without further
> > > > > administrivia or authentication,
or
> > more importantly, X can pass
> > > > > capability Y to any other agent Q,
and
> > Q can use that capability on
> > > > > behalf of X.
> > > > >
> > > > > Of course, we are trusting that X
> > protects capability Y and only
> > > > > hands it out to other agents Q
that it
> > trusts.
> > > > >
> > > > > A further assumption may be that
the
> > capability may be arbitrarily
> > > > revoked
> > > > > or suppressed at any moment by a
> > privileged process of some sort.
> > > > >
> > > > > On Thu, Mar 17, 2016 at 1:00 PM,
> > Carter Cheng
> > > > > <cartercheng at gmail.com> wrote:
> > > > >
> > > > > > I had looked into capabillity
based
> > security some years ago and
> > > > partially
> > > > > > implemented a system for doing
them
> > for a modified version of the dead
> > > > > > souls library in fluffos. I
never
> > quite finished it since I was
> > > > somewhat
> > > > > > uncertain how to mitigate the
> > complexity of transmitting capabilities
> > > > and
> > > > > > modifying the capability during
such
> > transmission to limit the
> > > > permissions
> > > > > > an object had. My limited
> > understanding of the capabilties versus
> > > > > > permissions approach is both
> > represent different ways of cutting up
the
> > > > > > security matrix (one vertically
and
> > one horizontally). I am not sure
> > > > what
> > > > > > you are quite meaning by a
> > capability. My understanding is that in
most
> > > > > > systems that are in research
these
> > are some sort of string denoting the
> > > > > > horizontal or vertical slice of
the
> > matrix and that transmission
> > > > involves
> > > > > > copying a portion of this string
> > into a new object. The problem I think
> > > > > > would be in designing a simple
> > approach for copying a "portion" of the
> > > > > > string and specifying which
portion
> > in order that less technically
> > > > savvy
> > > > > > users (which includes a lot of
mud
> > adminstrators and coders) would know
> > > > > > what to do when asked to supply
a
> > substring of the original string.
> > > > > > I guess I don't mud that much
> > nowadays so I haven't tried finishing my
> > > > > > implementation but that was the
main
> > problem I was running into.
> > > > > >
> > > > > > Regards,
> > > > > >
> > > > > > Silenus.
> > > > > >
> > > > > > On Thu, Mar 17, 2016 at 1:01 AM,
> > <bart at wotf.org> wrote:
> > > > > >
> > > > > > > A few comments on this:
> > > > > > > - you can't protect against
> > stupidity but
> > > > > > > for any security system a
fail-
> > safe approach
> > > > > > > should be used, put
differently,
> > doing
> > > > > > > dangerous things should take
> > enough work to
> > > > > > > not just happen by accident.
The
> > very large
> > > > > > > majority of security issues
are a
> > result of
> > > > > > > this not being done properly
by
> > many
> > > > > > > security systems.
> > > > > > >
> > > > > > > - doing all security checks in
the
> > wiztool,
> > > > > > > I'd rather think a security
check
> > should be
> > > > > > > done as close to the resource
> > needing
> > > > > > > protection to ensure as few
ways
> > to bypass
> > > > > > > those checks as possible.
> > > > > > >
> > > > > > > - having the object to which a
> > capability is
> > > > > > > given registered on the
'badge'
> > and hence
> > > > > > > requiring a formal interface
to
> > pass on a
> > > > > > > capability seems akin to
putting a
> > name and
> > > > > > > picture (and nowadays
biometric
> > info) on a
> > > > > > > badge, and seems a really good
> > idea if the
> > > > > > > purpose is to verify the
holder of
> > the
> > > > > > > badge.
> > > > > > >
> > > > > > > This can be done with a kernel
> > service but
> > > > > > > if the data is centralized
this
> > has a
> > > > > > > potential of not playing well
with
> > hydra.
> > > > > > >
> > > > > > > Bart
> > > > > > >
> > > > > > > On Wed, 16 Mar 2016 01:08:39
> > -0500, Jared
> > > > > > > Maddox wrote
> > > > > > > > > Date: Wed, 9 Mar 2016
12:29:43
> > -0800
> > > > > > > > > From: Raymond Jennings
> > > > > > > <shentino at gmail.com>
> > > > > > > > > To: All about DGD and
Hydra
> > > > > > > <dgd at dworkin.nl>
> > > > > > > > > Subject: Re: [DGD]
capability
> > based
> > > > > > > security?
> > > > > > > > > Message-ID:
> > > > > > > > >
> > > > > > >
<CAGDaZ_r3VdEPv=bh6cP+eHLbWpG2z7-
> > > > > > >
> > tTZNC1S8krKZj5VJq0A at mail.gmail.com>
> > > > > > > > > Content-Type: text/plain;
> > charset=UTF-8
> > > > > > > > >
> > > > > > > > > I figured that the
> > construction,
> > > > > > > configuration, and destruction
of
> > > > > > > > > capabilities and their
handles
> > would be
> > > > > > > the perview of trusted code
(like
> > a
> > > > > > > > > microkernel) and then its
at
> > the
> > > > > > > discretion of the code taking
the
> > caps on
> > > > > > > > > what they do with the
actual
> > > > > > > handles...and that if they
screw
> > it up its
> > > > > > > > > their own fault.
> > > > > > > > >
> > > > > > > > > Is it valid to say "I
> > guarantee the
> > > > > > > security that nobody will be
able
> > to
> > > > > > > > > use this capability unless
you
> > let them,
> > > > > > > but if you give it away you're
on
> > > > > > > > > your own"?
> > > > > > > > >
> > > > > > > >
> > > > > > > > "I guarantee security
against
> > all but your
> > > > > > > own stupidity"? I think
> > > > > > > > that sort of thing works
it's
> > way into
> > > > > > > most user agreements.
> > > > > > > >
> > > > > > > > > Date: Wed, 9 Mar 2016
22:31:13
> > +0100
> > > > > > > > > From: bart at wotf.org
> > > > > > > > > To: All about DGD and
Hydra
> > > > > > > <dgd at dworkin.nl>
> > > > > > > > > Subject: Re: [DGD]
capability
> > based
> > > > > > > security?
> > > > > > > > > Message-ID:
> > > > > > >
> > <20160309210855.M49546 at bartsplace.net>
> > > > > > > > > Content-Type: text/plain;
> > > > > > > charset=utf-8
> > > > > > > > >
> > > > > > > > > It depends. If something
wants
> > to check
> > > > > > > if your object has a certain
> > > > > > > > > capability, and you
present it
> > your
> > > > > > > badge, itstrivial for the code
> > checking it
> > > > > > > > > to clone it and reuse it,
> > unless you
> > > > > > > actively prevent that. What I
> > mentioned
> > > > > > > > > may be a way, registering
in
> > the handle
> > > > > > > which object it was given to.
> > > > > > > > >
> > > > > > > >
> > > > > > > > This could be tended to with
a
> > kernel
> > > > > > > service instead.
> > > > > > > >
> > > > > > > > Beyond that, if most or all
code
> > can
> > > > > > > create capability objects to
> > > > > > > > represent whatever
capabilities
> > it has,
> > > > > > > then objects can use it to
> > > > > > > > implement security layers.
> > > > > > > >
> > > > > > > > > Date: Wed, 9 Mar 2016
17:05:56
> > -0800
> > > > > > > > > From: Raymond Jennings
> > > > > > > <shentino at gmail.com>
> > > > > > > > > To: All about DGD and
Hydra
> > > > > > > <dgd at dworkin.nl>
> > > > > > > > > Subject: Re: [DGD]
capability
> > based
> > > > > > > security?
> > > > > > > > > Message-ID:
> > > > > > > > >
> > <CAGDaZ_p3OHFkUMJgs2DSx-
> > > > > > > 4YgctFJ5Lf-c5a+3-da-
> > F6qDPvnw at mail.gmail.com>
> > > > > > > > > Content-Type: text/plain;
> > charset=UTF-8
> > > > > > > > >
> > > > > > > > > ooh...good point
> > > > > > > > >
> > > > > > > > > capabilities will probably
> > need their
> > > > > > > own ACLs that can be
manipulated
> > by
> > > > > > > > > the objects thereon.
> > > > > > > > >
> > > > > > > >
> > > > > > > > I think capabilities should
> > ideally be
> > > > > > > carried around inside wiztools
> > > > > > > > & such: if a security check
> > needs to be
> > > > > > > done, the wiztool can do it
> > > > > > > > transparently.
> > > > > > > >
> > > > > > > > If arbitrary pieces of code
can
> > create the
> > > > > > > wiztools, then they can
> > > > > > > > also strengthen the security
of
> > the
> > > > > > > wiztool.
> > > > > > > >
> > > > > > >
> >
____________________________________________
> > > > > > > >
> > > > > > >
> >
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> > > > > > >
> >
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> >
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