Re: Identity Permission and Code Access Permission classes

From: Novice (6tc1ATqlinkDOTqueensuDOTca)
Date: 08/23/04 

Date: Mon, 23 Aug 2004 06:09:02 -0700

I'm really just trying to get a better grasp of when it would be appropriate
to use the Stack Walk Modifiers. I guess, they are appropriate just to
lock-down your application/libraries - but that ultimately it is the
responsibility of the computer hosting the application to ensure access is
limited.

What are your thoughts?

Novice

"Nicole Calinoiu" wrote:

> I'm still not sure what your ultimate goal is here, so it's a bit difficult
> to say whether the information in the P&P document is really relevant. It
> would help quite a bit if you could better describe why you want to protect
> the contents of this directory and against what type(s) of threat you
> believe it requires protection.
>
> My guess so far has been that this is a configuration directory for your
> application, and you want to protect its contents from modification by any
> code other than your own. If so, within-code protections (whether
> imperative or declarative) are only a partial solution, addressing only
> possible luring of your code to perform undesired actions. However, even
> wrt to this particular goal, use of StrongNamePermission alone isn't
> necessarily particularly useful since it's trivial to bypass. It can,
> however, be sufficient to counter certain types of threats. So... Exactly
> what kind of potential misuse are you trying to protect this directory
> against?
>
>
> "Novice" <6tc1ATqlinkDOTqueensuDOTca> wrote in message
> news:9E20FDC3-2635-4345-A12C-04DC95205C4F@microsoft.com...
> >I believe this is information I was looking for:
> > http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnnetsec/html/THCMCh08.asp
> >
> > Go to the section "Using Stack Walk Modifiers". Basically it states that
> > you can use the security policy, but that you can also achieve the same
> > effect programmatically in your code.
> >
> > If the above seems inconsistent with what I was originally asking - please
> > let me know because it may be that I misunderstand the documentation.
> >
> > Thanks,
> > Novice
> >
> > "Novice" wrote:
> >
> >> What I meant is that I could achieve this same functionality by writing
> >> code
> >> (imperatively) such that:
> >> if (publicKeyEqualsExpectedValue){
> >> allowWriteToHardDisk();
> >> }
> >>
> >> And again the same code could be written in declarative statements. Of
> >> course the assumption is that you have access to the source code
> >> otherwise
> >> you wouldn't be able to write the declarative or imperative statements to
> >> begin with.
> >>
> >> That is why I said it isn't "clean" since I would see putting the above
> >> statement into every assembly as a hack.
> >>
> >> But my real question was if there was a way to create a declarative
> >> statement like the one I posted:
> >> [StrongNameIdentityPermission(SecurityAction.LinkDemand,
> >> PublicKey="00240000048...97e85d098615")]
> >>
> >> And add something to the above or following the above that would also
> >> indicate that the application could only write to:
> >> c:\somedirectory\
> >> if it had the above PublicKey.
> >>
> >> I.E. is there a way to do the above in the source code for an application
> >> and use the PublicKey (a piece of evidence) to restrict an assembly's
> >> privileges/permissions.
> >>
> >> I think this could be achieve using the code access permission request
> >> operations (request, assert and deny). This of course assumes that the
> >> security policy would allow that level - however, assuming the policy
> >> allowed
> >> it - couldn't you write code such that you deny write access to that
> >> directory if the PublicKey isn't what you require?
> >>
> >> Thanks,
> >> Novice
> >>
> >>
> >> "Nicole Calinoiu" wrote:
> >>
> >> > Not sure what you mean by "I know this could be done using imperative
> >> > security" since, well, it's not. <g>
> >> >
> >> > Setting a machine to only allow access to a directory by assemblies
> >> > signed
> >> > with a specified key is certainly possible, but it's not done by
> >> > imperative
> >> > or declarative CAS checks in some other assembly's code. It's only
> >> > accomplished by setting policy. Otherwise, code that doesn't pass
> >> > through
> >> > your application wouldn't be subject to the limitation.
> >> >
> >> >
> >> >
> >> >
> >> > "Novice" <6tc1ATqlinkDOTqueensuDOTca> wrote in message
> >> > news:4E09C5AF-CECE-4C0A-BBD4-374A3E55DB14@microsoft.com...
> >> > > If I wanted to ensure that a particular assembly (or set of
> >> > > assemblies) as
> >> > > dictated by something in their evidence got certain code access
> >> > > permissions
> >> > > could I do this both in the security policy on the host machine or
> >> > > using
> >> > > declarative security (I know this could be done using imperative
> >> > > security -
> >> > > but it is not as "clean" as declarative security).
> >> > >
> >> > > To be more specific I would like to write a declarative security
> >> > > statement
> >> > > like the one below:
> >> > > [StrongNameIdentityPermission(SecurityAction.LinkDemand,
> >> > >
> >> > > PublicKey="00240000048...97e85d098615")]
> >> > >
> >> > > such that only assemblies with a particular PublicKey (like the one
> >> > > above)
> >> > > could be given rights to access "c:\somedirectory\"
> >> > >
> >> > > I would prefer to do this using declarative security statements - a
> >> > > second
> >> > > question is whether this would be possible using the security
> >> > > administrator
> >> > > on the local machine.
> >> > >
> >> > > Thanks,
> >> > > Novice
> >> >
> >> >
> >> >
>
>
>

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