Secure protocol for permitting file writes?

[Nelson Chen]

I was thinking the other day about ways to safely permit an unknown
program to write to one's local disks, without opening up one's
machine to malicious attack. I believe such a scheme must be embedded
in some language like Javascript, ActiveX, Java, and so on for it to
work. What do you all think of the following protocol?

Have a standard header for all files created/modified with the
language. The header can be a 128 bit number.
Have a file write command that can only create new files, all of which
are created with the header, and overwrite files that contain the
header. Files do not containing this fixed header cannot be created or
written to, and attempts to do so trigger an error.
Have user-customizable parameters (requiring admin priviledges) that
specify which drives and folders are permitted to be accessed, and
which ones can ordinary users change access permissions to. In
addition, specify a maximum file size, and a "forbid writing if < X
bytes of space are left" option.

I probably have left some sort of hole or holes in this scheme. Can
someone point them out? Thanks.

Later,
Nelson Chen
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